auto cooling system flow rates and heat transfer


Staff member
have you ever read stuff posted on line and just shake your head at the lack of facts or in some cases outright MS-INFORMATION being posted?
Honestly I'm amazed at the common myths and out right ms-information that's constantly repeated over and over as if it were facts, and a bit mystified that so few people are willing to do any research, to determine actual facts backed up by repeatedly tested math.

these two pictures, below just point out common coolant flow routes


some of my least favorite myths
(1) you need to slow the coolant flow thru the radiator to allow time to cool the fluid moving thru it
(2) swapping from a 190F to a 160F T-stat will significantly reduce an engines tendency to over heat.

(3) removing the t-stat will cure over heating



adding an aux oil cooler with its own electrical fan,
and ideally a transmission fluid cooler with its own electrical fan,
would significantly reduce the heat load on the radiator and engine coolant


1. Doesn't coolant have to have more time in the radiator to cool?
No. But a lot of people still think so. We have come up with some explanations for the Doubting Thomas.

Debunking the I Can Have It Both Ways Theory

The water has to have "time to cool" argument is most common one we hear. In a closed loop system if you keep the fluid in the heat exchanger you are simultaneously keeping it in the block longer. Unfortunately, the block is the part that is generating the heat. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. The engine is still generating heat the whole time so why keep the coolant there any longer than you have to.
its CRITICAL to keep the trans fluid clean and ideally changed about every 70K miles and use of a auxiliary cooler that keeps the fluid temp under about 170F is going to extend service life a good deal longer
Debunking The Conscientious Electron Theory

We hear that the coolant has to stay in the system longer to cool but what is heat transfer really but conduction, convection and radiation of electrons. The fluid in your system transfers those electrons based principally on the source-sink differential and the exchange material's transfer rate. An electron moves at varying speeds - Bohr's model has it moving at 2 million meter/second and with a mere 11 million eV boost you can get and electron to 99.9% of the speed of light. Though they move at varying speeds physicists accept that electrons move really really fast. Far faster than the flow rate of the water pump. Your engine coolant's electrons do not know (or care) how fast you send them through the system - they just knows that the source is hotter than the sink and off they go.

Debunking Grandpa's Flathead Theory

"But wait a minute, I know Grandpa used to put washers in his flathead to slow the flow and cool his engine." We know people did this too. They still do it but the cooling benefit is not from the slower flow but the increase in dynamic pressure in the block that builds from the restriction. Consider that Grandpa had two flathead water pumps sending twice the volume through the same size radiator core. At some point Grandpa maxed out the throughput and began building pressure. Building pressure in his block helped reduce the onset of hot spots on his cylinder walls and formation of steam pockets in his block. This is a real benefit and does help cooling but is only realized when throughput nears capacity or is at capacity. While these restrictions may make sense when your rpm is excessive or your flow rate exceeds your heat exchanger throughput, they do not make sense for most applications. If you doubt this thinking then try this simple Ask Dr. Science experiment; clamp off the lower hose while you watch your temp gauge. Hopefully, you will debunk Grandpa's theory yourself before you experience vapor lock and melt your engine.
Simply put, you have a far better chance of keeping your cool with greater flow rate through your heat exchanger and exiting the system than holding it in your heat exchanger while generating heat in your engine block.
2. Why am I seeing erratic temperature swings?
If you experience erratic temperature most likely you have air trapped in your cooling system. Air rises to the top of the cooling system and gets trapped, potentially causing the cooling system to vapor lock. When the radiator is made the higher point in the system, the air will escape into the radiator and it will be vented out through the radiator cap and the overflow system. There are a couple of ways to resolve this and free the air.

Free trapped air via the vent plug Fill the system as normal with your antifreeze mixture. Use a 50-50 mixture of antifreeze and distilled water. Auto parts stores will sell in-expensive to determine the concentration of antifreeze in your system.
Find the small threaded plug with a hex fitting at the top of the water box where the upper radiator hose enters the engine. Loosen the fitting to the point where air starts to escape and inspect the thread sealant – re-apply as needed. Be sure to run your heater to allow water into the heater core.
Add antifreeze to replace the air being expelled through the plug.
As fluid starts to seep out of the plug tighten it up, top off the overflow tank, and you’re done. If you continue to get erratic temperature readings, or fail to get heat from the heating vents, re-open the screw and let any residual air to escape.
To vent a system in this method raise the car such that the radiator is higher than the water box. You can do this through jacks (and jack-stands, never support a vehicle by a jack alone), ramps, or a nice steep hill and parking with the nose of the car pointing up the hill.
You’ll need to let the car warm up so that the thermostat opens for the system to vent in this method. AVOID BURNS AND PROTECT YOUR EYES! - Never open the cooling system when hot. Let the car warm up from cold with the radiator cap removed. You may get some spillage while the coolant expands and the air bubbles out. This coolant will be hot.
Allow the engine to run, with the heater on (fan can be off or on low) until the thermostat opens and all the air is allowed to purge. Once the thermostat opens you will see the coolant level inside the radiator bubble and drop. Continue to add antifreeze to maintain fluid level. Again be careful as the coolant and any steam released by the system will be hot. Once the upper radiator hose becomes hot to the touch and no further air issues from the system carefully replace the radiator cap and ensure the overflow bottle is filled to the Max line.
Continue to allow the car to run to allow the temperature to stabilize. If you don’t have a temperature gauge allow the car to run until the fan cycles on and off at least once. During this time ensure there are no leaks from the system and that the upper radiator hose gets hot to the touch (especially close to the radiator). If not then allow the system to cool, and repeat the steps above to purge any remaining air.

NOTE: If you are not comfortable leaving the radiator cap off during warm-up then you can accomplish the same thing by leaving the radiator cap on and allowing the car to cool down after step four and then repeat steps one through four again, making sure the overflow bottle is maintained full. The heating and cooling cycle will push the air out through the overflow bottle and then suck coolant in to replace the air when the engine cools. The car must remain inclined for the whole procedure.
3. Why is my car overheating?

There is no one single answer for this question but here is a list of places to start to isolate the problem.

1. Before you do anything else, tune up the car. Many overheating cars are out of tune, running lean or with retarded timing. A lean fuel mixture will overheat your car. If your engine runs lean you can chase your tail looking for problems in the cooling system and never figure it out. The easy way to do this is richen your jetting a couple of steps. If the overheating is better, you're on the right track.

2. There is a lot of misinformation about ignition timing and cooling. Retarded timing contributes to overheating. Advanced timing helps cooling. Advance your initial timing a few degrees and see if it helps the car run cooler. However, if you advance to much you risk detonation and that too will cause you to overheat. If you start to detonate back off the timing. Overheating cars should always run vacuum advance. Vacuum advance helps cooling.

3. Radiators: Your radiator is the primary means to bring the engine temperature back to the optimal temperature. Radiators can be dirty, clogged, poorly designed, too small for the engine, fin density too great for the low rpm get the picture. We know a little bit about radiators too; visit The Brassworks FAQs page for more information.

4. Airflow. Inadequate airflow can cause overheating. You have to get the air through your radiator and out of the engine compartment. Obstructions to that airflow can cause a cushion of hot air to build around your block and engine compartment. A properly fit fan shroud sealed to the radiator helps to channel the air through your radiator.

5. Inadequate coolant flow. If you are overheating at idle, stop and go traffic, on grades or towing you might benefit from higher flow rates through the radiator. reducing the cycle time between the engine and the heat exchanger provides more opportunity to shed heat. Hi Flow water pumps and hi flow thermostats create these incremental opportunities.

6. Modified gear ratios: Generally speaking lower ratios give slower acceleration, higher top speed and less braking power – Higher ratios give more acceleration, less top speed and more braking power. Changing gear ratios may generate more heat in the engine and potentially cause overheating.

7.Coolant composition. Most people run 50/50 for the increased boiling point and the engine block preservation. It is worth noting however that the specific heat capacity of ethylene glycol based water solutions is less than the specific heat capacity of clean water. For a heat transfer system with ethylene glycol manufacturer recommend that the circulated volume must be increased compared to a system with clean water.

In a 50% solution with operational temperatures above 36 degrees F the specific heat capacity is decreased with approximately 20%. The reduced heat capacity must be compensated by circulating more fluid.

An ethylene glycol mixture does raise the boiling point and will lubricate the water pump to prevent corrosion in system. Some people change the ratio of these fluid in hot season and when the weather cools return to 50/50.

8.Cooling the transmission is added work for a radiator. Do not obstruct airflow or heat the air passing over the radiator by placing the cooler in front of the radiator. Transmission and engine oil coolers constructed within the radiator tanks can also tax your cooling system by introducing a heat source in the tank. Using external coolers may help because they take the heat out of the cooling system.

9. The elusive manifold vacuum leak. Trouble at idle may point to a manifold vacuum leak. If you find you're too fast an idle speed, rough idle or stalling, misfiring on acceleration or adjustments to your carburetor seem to have limited effect than you may have a vacuum leak causing overheating.

10.Use a better grade of gas. If you are not running premium fuel and experience overheating a higher grade may help. If there is no improvement, try advancing your timing a few degrees. A little extra octane will allow you a little extra timing without getting into detonation. Earlier engines were designed for better gas than is sold today.

11.Head gasket leaks from the cylinder to the water jacket are a definite cause of overheating. That's bad news and a whole lot of work.

12.A stuck thermostat. Many thermostats are designed to fail in the open position but thermostats have also been known to stick partially open and impede coolant flow.

13.A slipping water pump belt can slow the flow rates from the water pump and impede coolant flow resulting in overheating.

14.A fan blade with insufficient blade count or incorrect pitch may not draw enough air. The fan can also be too far from the core or located too far inside a fan shroud which then traps the air, moderates the heat and heat exchange is diminished.

15.Headers without thermal coating can cause overheating.

16.A stretched timing chain or belt can cause overheating.
4. If I am overheating; do I even need a thermostat?

Running without a thermostat is a slippery slope. The thermostat provides drag on the water flow which increases the backpressure the water pump. This additional pressure, over and above the nominal static pressure of the radiator cap raises the boiling point of the systems coolant. The higher temperatures helps suppress localized film boiling at hot spots such as around the exhaust port.

The transition from nucleatic boiling (bubbles of steam originating from irregularities on the surface) to film boiling (where the hot surface is coated with a film of steam) is called Departure from Nucleatic Boiling or DNB. DNB is very very bad because steam is a good insulator compared to water. Once DNB occurs, the area under the steam gets hotter because the steam fails to remove engine heat. The adjacent metal, which is still wetted, heats therefore from conduction. DNB happens there. The process spreads until substantially all the coolant-wetted surfaces are insulated by a film of steam. Uh oh - the engine overheats. To make matters worse, this steam buildup in pressure will forces the radiator cap open spilling coolant to a recover can (or the street). The loss of coolant from the system escalates the whole problem and the situation get progressively worse.

The second issue is that of water pump cavitation and surge. Operated a pump at high RPM with insufficient head pressure provided by the frictional losses in the coolant passages and the thermostat creates a greater likelihood that the pump will either cavitate or surge. Cavitation is the condition where localized boiling or degassing occurs as the fluids exits the impeller vane and pressure changes. Surges are the result of unstable flow rates.

Both cavitation and surging are destructive elements to the engine block and cylinder wall. How destructive? Cavitation's collapsing bubbles function like a sand blaster that will eventually erode away impeller material and block wall surface. Surge can do the same thing and the added vibration can stress the impeller enough to break it. What often looks like corrosion damage to the impeller when the housing is intact may actually be cavitation damage.
5. When should I check my cooling system?

The best time to inspect your heater and radiator hoses is cooler weather. Less obvious signs of decay can be seen and felt by grabbing hold of a cold radiator or heater hose and giving it a good squeeze. Brittle or cracking material, a spongy feel, or a hose sticking to the inside of itself are bad signs.
6. Can I block off my BBC bypass to the intake manifold?

Blocking off the bypass will route the coolant directly to the radiator which is good for heat exchange but remember the bypass circulates water until the t-stat opens. This routing helps circulate the fluid and raises block pressure which prevents the formation of hot spots in the engines. Failure to run bypass may result in excessive pressure buildup at the t-stat which can cause it to open early or potentially cause gasket leak.
7. What is that Knocking sound?

This is not really a cooling question but it made the list...

Knock or pinging or detonation or spark knock is caused when the air/fuel mixture ratio in the cylinder causes the fuel t o burn unevenly. Fuel normally burns in pockets and when each pocket of fuel burns, a shock occurs that burns the next until all the fuel is burned in that stroke. When a knock is present, the pockets don't burn evenly, causing the cylinder wall damaging shock waves that can damage the piston itself. The pocket formation also creates the common "pinging" noise that is often described when knock is present.

You also can get a knock sounds from the following:

piston slap
worn piston bearings
worn wrist pins
loose or worn lifters
loose or worn rockers
low octane gas
carbon deposits on cylinder walls
incorrect spark plugs
intake leak
bad bearings on the crankshaft
thrown rod
If you have a belt slipping do realize they make dual v-belt belt alternator pulleys and 3 and 4 v- belt crank pulleys and 3 v belt groove water pump pulleys



just a point many guys seem to over look, the fans run on electricity and a higher amp capacity alternator provides a good deal more current to spin those cooling fans, charge the battery, and provide current to the lights , Ive seen several cars with marginal cooling that had that cooling issue disappear once a 160-200 amp alternator replaced the stock alternator, the increased current allowed the cooling fans to spin a good deal faster at low engine speeds and the result was more efficient cooling.

one fact often over looked is that radiator designs vary wildly, and the number of fins per inch of surface area and width of radiator coolant flow tubes can significantly increase or decrease thermal heat transfer efficiency., fin counts vary from 8 to 22 fins per inch on various radiator designs Ive seen.
thus a radiator might measure say 18" tall by 24" wide but depending on design, and fin and tube count, might actually have a radically more or less efficient heat transfer rate.obviously the best and surest way to find out if a radiator, shroud and fan combo cools the engine effectively will be to install and run the component parts you have under the current applications limitations for real world testing and if it needs upgrading your dealing in proven facts vs guessing
ID also point out that all radiators collect crud and become restrictive to flow and much less effective at transferring heat to outside air flow over time, especially if the wrong coolant or water containing excessive mineral content are used so you might want to have yours cleaned out, rebuilt or replaced, if thats needed, after taking it out, an inspection indicates the correct course, a new aluminum radiator, in the largest size quality, radiator, that fits you can afford, is usually a good idea, if it needs replacing



I find it rather amazing that many guys (even a few corvette owners) don,t realize that the oil cooler between the block and oil filter does remove a noticeable amount of heat from the engine oil,or that in some cases that they even have an oil cooler factory installed. ITS OIL FLOW that absorbs and initially transfers heat away from the bearings and valve train not coolant.

my 1985 corvette came with a factory oil cooler, that runs engine coolant through separate but contacting internal passages, this warms the oil faster getting it flowing but tends to reduce the heat engine oil can reach as it absorbs oil heat effectively transferring it too the engine coolant on the car, where its transferred too air flow through the radiator, this does a decent job if your cruising but not on a high performance application where a larger transmission fluid cooler does a significantly better job

obviously this cooler mounts between the block and oil filter and runs coolant through separate passages with a common wall to the oil flow so the coolant which is generally 10F-20F cooler than the oil will absorb some of the oils heat load. (use of the extra long oil filter,



I don,t know where they sell these, finned aluminum filter covers now ,a few years back these were $20 each and significantly longer that this picture shows,
in fact they were the length of the long oil filter ,and believe it or not the combo of the longer oil filter and finned cover dropped my oil temps an additional 5 deg F , EASY TO PROVE by simply removing and replacing the slip on finned cover several times after keeping detailed records while cruising the interstate at a steady 70 mph (not a big difference but for $20 well worth it!

and a larger capacity baffled oil pan, also helps as it exposes more surface area to cooler under the car air flow)

those aluminum finned tube coolers work, are reasonably cheap, very durable ,but a bit restrictive

but they don,t cool trans fluid or oil no where near as efficiently/fast as the larger fan equipped coolers with the AN#8 line size
and in either case finding a place to mount any cooler where you can keep it out of sight and still easily access fresh outside air flow,
is usually a problem for most people

one of the most common mistakes less than experienced performance enthusiasts, face and very commonly over-look, is the fact that the internal cross sectional area on many hydraulic and fuel line fittings are considerably more restrictive to flow that the fuel limes or hydraulic lines inside diameter they were designed to be used with, and it varies a great deal between different manufacturers, now ideally the fittings internal passage cross sectional area is both consistent and the same or greater that the tube or hydraulic line size, it listed to match, , so a 1/2" inside diameter fuel line, or hydraulic lines?hoses, for example should have components for the connections and fittings that have significantly smaller internal cross sectional areas, it does you very little good to use lets say, AN#8 or half inch fuel lines if the internal cross sectional area of the connections and fitting used with those lines is only 3/8" or smaller in cross sectional area,this is an area where dealing with a local hydraulic supply shop that has the correct tools and fittings to custom fabricate your fuel lines, coolant or lubrication lines is a very good idea!
talk to a local professional at your local hydraulic supply, measure accurately, take the time to explain what your trying to accomplish and take several pictures to show them what your doing, and get them too fabricate any high pressure fuel or coolant lines and related fittings




Up to 45 GPH= 3/4 GPM = 5/16" or -04 AN

Up to 90 GPH = 1.5 GPM= 3/8" or -06 AN

Up to 250 GPH =4.2 GPM= 1/2" or -08 AN

nearly ideal for transmission and oil coolers :D
Up to 450 GPH =7.5 GPM= 5/8" or -10 AN

Up to 900 GPH = 15GPM 3/4"or -12 AN












the rotating assembly bearings ,wrist pins and complete valve train,valve springs, lifters, valves and valve guides and the pistons and rings are where a great deal of the engine heat is generated, and those components are initially cooled with oil flow that absorbs and transfers the heat collected , and transported from those components to the block and coolant, so having a constant flow of pressurized oil flow over those parts are mandatory for maximum durability.thus adding a larger capacity baffled oil pan and an oil cooler will generally enhance and extend an engines life span.

clutch fans have a viscus clutch that spins the fan based against the resistance its working against
the fans generally spin the fastest at about 2000-3000 rpm
,so from idle to about 2500 rpm fan speeds increase along with but not directly related too engine rpm,
much above that rpm the resistance won,t allow the fan speeds to increase nearly as fast as rpms increase
so the clutch fans do soak up some engine power , but not nearly as much as a solidly mounted fan would have.
generally the more blades on a quality clutch fan, the better it cools
I generally used to look for the clutch fans of caddys and buicks as many will mount to chevy water pumps with minimal or no mods

most were available from salvage yards dirt cheap in years past you ideally want something similar to this
don,t forget a matching fan shroud that matched the radiator and fan diameter,greatly increases cooling efficiency

read the links and sub-links

"A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.

Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it."

The quote is from Stewart Components website.

If your replacing a damaged or missing fan shroud ,it doesn,t need to be an EXACT match,to the original O.E.M. component
but it should be an IMPROVED design over what its replacing'
in both structural strength and ideally in cosmetic appeal,
a bit of custom fabrication if done correctly,
will add rather than detract from the over all builds visual and functional presents,
ideally you want people to look at what you've done and think
"WOW! why didn,t I think of that!.... DAMN THATS IMPRESSIVE"
rather than "
what the hell was that guy thinking when he installed that crap!"

and sometimes
the difference is only in a few extra minutes grinding welds,
the type of fasteners used, the care taken in the fabrication and careful fitting,

thinking through the over all design,
or a bit of matching paint




Dorman 620-118 Radiator Fan Assembly

1995-96 corvette cooling hoses




THE SECRET to a good solder seal, on a radiator joint, is a totally clean metal (FAIRLY THICK COPPER) surface and the correct solder alloy for the application
most aluminum radiators are EPOXY SEALED NOT WELDED,(yes the better versions are welded)
the problem here is that acid dips to clean the surface with alkaloid dips for PH stabilization and raid steam cleaning of metal surfaces followed by use of , lead acid, or silver solder either makes the EPA and OSHA nuts or its darn expensive.
aluminum is an acceptable but not the best quality substitute, as it rapidly metal fatigues and its difficult to weld if corroded
if your going to use a valve train cooling oil flow to cool the valve springs ,

you'll need to dissipate the heat that oil flow collects as it runs over the surface of those hot valve springs and a combination of a higher capacity baffled oil pan ,

and an auxiliary oil cooler to make transferring the absorbed heat load the oil carries away from the upper engine is almost 100% mandatory if your expecting the oil to cool the valve train for very long.
Id point out that you'll almost certainly want to use an oil cooler that's as large as you have room to effectively use and having a powered fan to increase air flow and heat transfer efficiency will help, bu remember the line size between the engine cooler and back to the engine will generally slightly restrict flow so, I,d advise at least a AN#8 or 1/2" internal cross sectional, size oil or hydraulic lines designed to handle 300F temps and pressure levels with a significant safety margin above what the engine produces, and having large remote mounted oil filter(s) won,t hurt either.
Yes they make dual transmission fluid and oil coolers so you might want to consider that option if you have an automatic transmission and Id sure suggest a fluid temp gauge that accurately measures transmission fluid and a separated gauge for oil temperatures.
IM currently using this transmission fluid cooler on my 1985 corvette but have used others in the past, and a dual cooler like this certainly has some advantages , if you need both oil and transmission fluid cooling.

first Id point out that 210-220F while above the temps your used to seeing on the older muscle cars is NOT exceptionally hot, in most modern car engines and while it certainly can be reduced its also not likely to cause you any problems if its controlled and stays under that 220f most of the time, oil should exceed 213F to boil out moisture that can cause acids in the oil to form

(1) the larger the heat transfer surface area the better the system tends to operate, but a minimum of about 1.5-2 square inches of radiator fin area exposed to effective air flow per cubic inch of displacement is generally required

(2) oil does much of the initial heat transfer in the engine, keeping the oil cooled too no more than about 15F above the coolant temp, and it reduces the heat load on the radiator coolant, so adding a high capacity 7-8 quart oil pan with its greater surface area that dissipates heat,and an added fan equipped, remote mounted oil cooler can dramatically reduce engine operational temps.
if you have an automatic transmission the cooler in the lower radiator adds considerable heat load, adding an auxiliary trans fluid cooler helps improve the engines cooling efficiency.



(3) air flow rates are critical so a well designed fan shroud and a fan(s) easily capable of pulling 3000 plus cubic feet per minute in air flow is very helpful

the answer too what cooling system is most likely to both cool the car/truck efficiently and fit your budget,would mostly depend on your budget limitations,
but a large 3-4 tube aluminum radiator with a a 140-to-200 amp alternator
taking advantage of all your options is a smart way to reproach the issue of correctly controlling, and maintaining a stable and predictable engine heat level, thus installing a larger capacity racing style oil pan and an auxiliary oil cooler with an electrical fan, will significantly increase the engines ability to rapidly dissipate heat even before that engine heat is absorbed by the engines cooling systems coolant. oil flow over a few of the hottest components like valve springs, bearing surfaces,and rocker arms absorb and transfer heat to the block, and oil pan as it flows, thus a larger oil capacity and a baffled oil pan with an extended sump is a good idea as the increased oil capacity and larger surface area of an enlarged sump area exposed too outside air flow can stabilize and allow a good deal of heat to dissipate to that outside air flow, as the air which can be well over 130F-170 plus F cooler that the engine oil that can be up to 250F plus in a racing engine





I'd point out that a 7-8 quart baffled oil pan helps cool an engine.
and dual or a large single electric fan with a matched ducted shroud and the ability to move,
2500 fcm-3000 cfm of air should provide adequate cooling for most engines.
adding an auxiliary oil cooler certainly helps

Keep in mind a well designed 7-8 quart baffled oil pan adds both durability and helps reduce cooling issues

and if you have an automatic transmission Id add a electrical fan cooled trans fluid cooler





a few links may help here
READING THE LINKS POSTED BELOW AND SUB_LINKS HELPS ... 3/p/HW769/ ... -transfer/ ... 1&ext=.pdf ... Tips_6.htm ... obiles.htm

keep in mind a great deal of most all initial heat transfer internally is the result of oil flow over moving surfaces like valve train and bearings adding a remote oil cooler and deep baffled oil pan can significantly lower heat loads on the radiator

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The Grumpy Grease Monkey mechanical engineer.
Staff member
Why make a Hi Flow Water Pump?
FlowKooler introduced the first hi flow pumps to the aftermarket and continues to improve impeller design to this day. Increased flow helps cool a hot engine because it reducing the cycle time between the heat source and the heat sink creates more opportunities to shed heat and drop engine temperatures. FlowKooler’s impellers are precision machined from billet aluminum to flow more coolant. They feature larger diameters, tighter vane-to-casting clearances, shrouding, porting and have incremental vanes. These design elements are incorporated into the impeller for one purpose; to generate more flow to cool hot engines. Each impeller is anodized with a Military grade Type II Class II anodized surface coating to protect against corrosion and the damages of electrolysis. Engines at idle, engine cruising at slow speeds or engines stuck in stop-and-go conditions have something in common; lower coolant flow rate and reduced air circulation through the radiator. Flowkooler pumps increase the flow and create highway-speed flow rates. The pumps continue to deliver higher flow all along the rpm curve and when system throughput is maximized, FlowKooler pumps build block pressure. Increasing the block pressure by as much as 22% reduces hot spots on cylinder walls, prevents the formation of steam pockets in the engine block and prevents the cavitation of the impeller. FlowKooler hi flow water pumps’ incremental vanes carve up the workload and conserve as much as 2.2% horsepower. Because FlowKooler pumps reduce engine temperatures as much as 30 degrees, they are frequently recommended by aluminum radiator manufacturers as a necessary tool of cooling for hot engines with thin radiator cores and reduced capacity.
Who uses a Hi Flow Water Pump?
Whether it is in stop and go traffic, a slow moving parade, in line at a car show, off road on the trails or hauling a heavy load up a grade all cars face reduced airflow through the radiator at slower speeds. We have sold pumps to muscle car owners, street rodders, off road rock crawlers, people towing RVs and horse trailers, boat owners and even Propane powered trucks!
The Benefits of Hi Flow Water Pumps
1. Lower Engine Temperatures.

Most engines keep cool at highway speed. It makes sense; the engine is turning the fan at with higher rpm and the water pump is spinning rapidly and sending coolant through the radiator. The radiator has good airflow at highway speed. Of course engines stay cooler. However, at low speed, it is a different story; engines tend to heat up when you face limited airflow, trapped airflow and slower moving coolant. These condition exist in stop-and-go traffic, at car shows, rock crawling or off-road or in any vehicle under a load. FlowKooler has focused on increasing the flow rates at lower rpms to resolve low speed overheating. At idle our pumps pump more than twice other pumps and we outflow “performance” pumps by 20%. FlowKooler pumps take the coolant out of the engine and put it in the heat exchanger or radiator to keep your cool.
2.Eliminate Hot Spots and Steam Pockets
Engine blocks machined with limited or no cooling jacket can result in steam pockets and hot spots. This design is great for getting more bore out of your engine but notorious for overheating. At idle the creation of a hot spot at the top of the cylinder may be enough to cause pre-ignition. At the extreme steam pockets can lead to detonation (hot spots in the cylinder wall); detonation leads to broken parts. At high rpm the coolant moves through the block fast enough to prevent any steam pockets from forming. FlowKooler pumps suppress engine hot spots and steam pockets by sending more coolant through the system at low speed and simultaneously raise engine block pressure 22% to prevent their formation.
3. Ending Early Cavitation
Cavitation is the formation of vapor bubbles in a flowing liquid where the pressure of the liquid falls below its vapor pressure. When the vapor bubble that forms rapidly collapses it produces a destructive shock wave that damages the interior wall of the engine block and other components, causes vibrations and noise and results in a loss of flow efficiency. FlowKooler impellers tighten clearances to reduce "slop" in the casting chamber and build pressure. This helps to prevent the onset of cavitation.
4. Stop the Knock
Knock, detonation or ping…call it what you want - it is a problem. Ping heard when the engine is shut off may be the result of pre-ignition. Pre-ignition results from the air/fuel mixture igniting in the cylinder before the spark plug fires from an ignition source other than the spark. Hot spots can damage to the point they actual burn holes right through the top of pistons. Causes include:
  • Carbon deposits form a heat barrier
  • An overheated spark plug
  • A sharp edge in the combustion chamber or on top of a piston
  • A sharp edges on valves
  • A lean fuel mixture
  • Low coolant level
  • Slipping fan clutch
  • Failed electric cooling fan
Flowkooler hi flow pumps help reduce engine temperatures and stop the after run or pinging characteristic of a pre-ignition condition. Knock can also occur when the combustion of in the cylinder starts off correctly with spark plug ignition but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front ignition. It will cause the peak of the combustion process to occur outside of the optimum moment and results in a characteristic metallic "pinging" sound. The other consequence is an increases in cylinder pressure which can be harmless or destructive to rings piston or bearings.
5. Gain Horsepower
A poorly designed water pump casting and impeller can result in wasted horsepower. FlowKooler pumps are designed to move water more efficiently from the radiator to the block to keep you cool. Some refer to the improvement in flow efficiency as a gain in horsepower, other call it a conservation of horsepower. Whatever you call it, FlowKooler pumps are 32% more efficient than OEMs which means less horsepower is used to turn them.
Hold on...doesn't the coolant have to have more time in the radiator to cool?
No. But a lot of people still think so. We have come up with some explanations for the Doubting Thomas.
Debunking the I Can Have It Both Ways Theory

The water has to have time to cool argument is most common one we hear. In a closed loop system if you keep the fluid in the heat exchanger you are simultaneously keeping it in the block longer. Unfortunately, the block is the part that is generating the heat. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. The engine is still generating heat the whole time so why keep the coolant there any longer than you have to.

Debunking The Conscientious Electron Theory

We hear that the coolant has to stay in the system longer to cool but what is heat transfer really but conduction, convection and radiation of electrons. The fluid in your system transfers those electrons based principally on the source-sink differential and the exchange material's transfer rate. An electron moves at varying speeds - Bohr's model has it moving at 2 million meter/second.But let's just agree it is fast (really really fast). Far faster than the flow rate of the water pump. Your engine coolant's electrons do not know (or care) how fast you send then through the system - they just knows that the source is hotter than the sink and off they go.

Debunking Grandpa's Flathead Theory

"But wait a minute, I know Grandpa' used to put washers in his flathead to slow the flow and cool his engine." We know people did this too. They still do it but the cooling benefit is not from the slower flow but the pressure that builds from the restriction. Consider that Grandpa had two flathead water pumps sending twice the volume through the same size radiator core. Ask him and he might tell you his overheating woes were really as he tore up the track at high speed. Grandpa caused cavitation in his pump by with higher rpm and unrestricted flow and the result was overheating due to cavitation.

Restricting his flow with a washer build up his pump pressure and pressure in the block helped reduce the onset of hot spots on his cylinder walls and formation of steam pockets. So Grandpa was on to something but just not for the reason most people think. This restrictions makes sense when your rpm is excessive but it rarely makes sense normal driving conditions.

If you doubt this thinking then try this simple Ask Dr. Science experiment where you restrict the pump on the suction side; just clamp off the lower hose while you watch your temp gauge. Hopefully, you will debunk Grandpa's theory yourself before you experience vapor lock.

Restriction is not all bad if it serves to prevent cavitation. Cavitation occurs when a pump turns so fast that you generate lower pressure and air bubbles or vapor forms. These bubbles eventually implode and damage the engine block wall and impeller. Rapidly spinning the impeller can literally rip the air from water but may not actually move the fluid, it's tantamount to turning an eggbeater in a paint bucket. Restricting the fluid flow to raise system pressure in the block may help prevent cavitation at higher RPM but is it necessary for most vehicles?

No. Most vehicles do not need to restrict flow because they do not reach or sustain high RPM. Additionally, thin aluminum radiators already restrict by design e.g. fewer rows of tubes. Restrict it further and you may as well hose clamp the lower radiator hose and we know how that works out. When you face Grandpa on the track you may want your washers, otherwise, keep them in the toolkit.

Simply put, you have a far better chance of keeping your cool with a greater flow rate through your heat exchanger than gathering heat in your engine block.
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Some intetesting tips by Flowcooler Grumpy.
Steam pockets hidden from view create hot spots in the cylinder heads that can lead to Preignition at Engine idle speeds.
1 month of summer left.
More 90-100 F days .


I spent a lot of time sifting through Pontiac forums, Ford Forums, Chevy Street & Full Drag Race, & Mopar Forums with guys running 440 wedge & 426 Hemi on the streets up to claimed 1250 HP.
Near all experienced overheating issues at 95-100 F.
Data is largely inclusive .

Electric fans used 99% Of the time.
They solved the guys by reverting bsck to Factory clutch fans & full shrouds.
Or 1 single 7-blade factory aftermarket racing flex fan.
The Flex fan is a near duplicate of the 1970-71 Chevy Corvette HD Cooling system option fan.
And Pontiac Firebird Trans Am HD Cooling system Power Flex Fan.
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Pictures of Factory Chevy & Pontiac Fans all are not online.
I have a few used ones samples here.

Electric CSR & Meizure drag racing water pumps are used by many with Moroso Water restrictor plates.
Despite advice to with no T-stat & water plate.


I have an 80 row Be Cool Radiator with 1-1/2" inch wide tubes in the Grand Prix.

The Big Griffin in the Corvette has 72 rows with 1-1/2 " wide tubes.


My new issue of Jegs Performance catalog came in today Grumpy.
What's stands out is Champion radiators is now rating them by HP Cooling levels.
400-600 HP 2- Row
600-800 HP 3-Row.
800-1200 HP 4-Row.

All Aluminium radiators.
Only Griffin rated their Racing Radiators by HP Cooling capacity prior.


The Grumpy Grease Monkey mechanical engineer.
Staff member

the heat transfer efficiency rate your engine runs at is determined BOTH by the efficiency of the vehicles cooling system and the t-stat opening temp
the t-stat is limiting flow below its rated temp, the cooling system efficiency, the rate the cooling system can transfer heat to the outside air flow, the outside air temp,
will determine the upper or running temp above the t-stat opening temp.

it might help if you think of it this way,
if you had the cars water pump inlet hose connected to a swimming pool,
and the engines output hose dumping back into the far side of that swimming pool
the engines coolant would enter the engine at (ROOM TEMP) and the t-stat would open once the pool water in the engine reached its temp setting, it would pick up heat as it traversed the engines coolant passages but with an unlimited volume of pool water at near room temp as a supply the t-stat would constantly open and close, and coolant temps your sensor showed would rarely exceed about 10 degrees more than the t-stat, even if the t-stat was a 160f or a 200 f, rated t-stat, unfortunately, all cooling systems don,t have a (unlimited ability to supply room temp coolant) so the temp runs at what ever temp the cooling system can operate, remember the outside air flow might be anywhere from -30f-110f in various areas of the usa, but thats always a considerably lower temp than the engines coolant so the radiator can transfer heat to the outside air flow. obviously the greater the difference in temp between the coolant exiting the engine and the outside air flow temp,naturally once the car/trucks up to cruising speed thaT ADDS TO THE AIR FLOW RATE THROUGH THE RADUIATOR OVE WHAT THE FANS Alone can supply in air flow rates, remembe the larger the surface area of the radiator ,and the higher the rate of air flow over the radiator surfa



you'll want too stop and think things carefully and measure accurately

its never a bad idea to measure the oil and transmission fluid temps during your cars operation, this is the most consistently accurate I.R temp gun I've used for testing
42545.jpg Extech Products
Wide temperature range from -58 to 1832°F (-50 to 1000°C)
any time that your dealing with a potential temperature issue or a trouble issue where , knowing the exact temperature vs what a gauge might say, it helps to have a handy and accurate infrared temp gun handy to locate and confirm heat, levels.





if your experiencing detonation issues that are cured by swapping to higher octane rated fuel, and you would prefer to use the lower octane , less expensive fuel, you should adjust your cars ignition advance combination , so that its advance curve has either less initial timing, or delaying the mechanical advance vs. rpm with some stiffer springs, or a combination of both might reduce the pinging under load at 2500-3500 rpm where its most commonly seen,. Does this detonation or pinging, only occur at WOT? If not, limiting the vacuum advance with a stop, or using an adjustable vacuum advance unit and raising the amount of vacuum required vs. the amount of vacuum advance might be warranted also and installing a lower temp rated t-stat and adjusting the engine fuel/air ratio a bit richer may also help..


the guys have a point, best power and in many cases durability, is generally found at nearer 12.7:1 f/a ratio, I don,t ever remember your engine getting near that lean while we discussed getting it tuned up?


that, need for the coolant traveling through the engine,to take time to absorb and release heat, is
a complete myth, as long as the radiator has at least the minimum surface area that will cool the engine to about 200 f
with minimal air flow like the car sees sitting still only using the fans to supply air flow,the faster the coolant flows the more effective the cooling system becomes
the larger the surface area of the radiator, and number of fins per inch of surface area around the coolant transfer tubes,
and the higher the coolant volume in relation to the total percentage of coolant in the engine ,
the greater the volume of outside air mass passing over the fins and tube surface area,
the more effective the radiator can become, but remember OIL does much of the initial heat absorption and heat transfer ,
so adding an effective oil cooler with its own fan, significantly improves engine cooling efficiency
lets assume you really want this $180 ,
trans fluid or oil cooler,
you'll want too stop and think things carefully and measure accurately

Summit Racing Part Number:FLX-45908

Overall Height (in):10.500 in.

Overall Width (in):15.000 in.

Overall Thickness (in):4.000 in.
Flex-a-lite's fan-equipped, heavy-duty remote coolers offer a great combination of cooling power and freedom of mounting location, all at down-to-earth prices. Their tube-and-fin design is made up of efficient aluminum fins and multi-pass copper tubing. With their attached 800 cfm electric fans, they don't have to be mounted in direct airflow to work. They make their own breeze. So you can put them in just about any convenient, reasonable place and they'll still get the job done. There also are dual-circuit versions that accommodate two different fluids--such as engine oil and automatic-transmission fluid--in the same-size cooler. That's especially good for applications where space is limited or cooling needs for the fluids concerned aren't extreme. A manual control switch, air-conditioning override switch, and GatorClip mounting clips are available separately.
in this case you would make a test styra-foam block
10.75" tall
17.25"-to-17.5" wide
4.25" thick
if that fits where you intend to fit the fluid cooler you have a great indicator it will fit
obviously the cooler needs to mount to something sturdy so ideally the mount stand or brackets you custom fabricate will have it firmly and solidly located where you intended it to be!
SEPARATELY, and once you've verified clearances you order the components then measure and get custom lines fabricated

some of my least favorite myths

(1) you need to slow the coolant flow thru the radiator to allow time to cool the fluid moving thru it
(2) swapping from a 190F to a 160F T-stat will significantly reduce an engines tendency to over heat.

(3) removing the t-stat will cure over heating

total surface area of the radiator should ideally be at or more than about 1.5-2 sq inches per cubic inch of engine displacement.
in theory that requires about a 24 inch tall x 32 inch wide
496 x 1.5=744
24 x 32=768
obviously clearance issues fitting that large a radiator become a problem so multi tube radiator designs are rather common on performance applications



If you think about it a bit all a knock sensor does is retard ignition advance timing,
to the point the engine no longer detonates due to too much heat in the combustion chamber for the advance curve and fuel octane.
obviously if you have experience tuning a certain engine and your fuel octane is fairly consistent, you can change the ignition advance curve to match ,
the engines documented and tested power potential.
that does not mean a knock sensor is not useful , simply because fuel quality and engine cooling efficiency varies with outside air temps.
and your cars radiator and oil and trans fluid cooling efficiency, but a good tuner can avoid getting into detonation range, with a known engine combo, a high percentage of the time.
obviously boosting your fuels octane, and fuel to air ratio to cool the combustion helps so thats the first part of the equation,
retarding the cam timing reduces effective compression,
retarding the ignition curve will reduce cylinder heat and effective pressure,
all factors should reduce detonation,
easily 60% of the most common engine detonation is not in the normal adult humans hearing range
detonation damage is cumulative!
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The Grumpy Grease Monkey mechanical engineer.
Staff member
42545.jpg - Bing Shopping - Extech&utm_term=1100200223789&utm_content=All Extech Products
having the correct tool to verify the temps would be helpful
keep in mind



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The Grumpy Grease Monkey mechanical engineer.
Staff member
keep in mind , a properly designed fan shroud markedly increase radiator fan, air flow rate efficiency!
fans used without a properly matched fan shroud can lose 20%-30% of effective air flow rates through the radiator fins.
puller fan(S) are much more effective than PUSHER FANS used on any radiator!
you'll generally want a minimum of about 1.5 square inch of cooling fin surface area on your radiator or more per engine horse power!
radiator and shroud design do have a very measurable effect on heat transfer rates,
thicker cores with redundant coolant tubes can increase cooling capacity,
and the number and size of the radiator coolant tubes and number of fins per square inch,
does have a large effect on heat transfer efficiency!
the larger the radiator fins surface area and the higher the percentage of the total engine coolant in the radiator vs the engine block,
the more effective the cooling system tends to be!
keep in mind OIL FLOW does a great deal of the initial valve train and bearing surface heat transfer,

thus adding an effective separate oil cooler to any engine,
can go a long way to reducing engine temps and reducing the heat loads the radiator has to deal with.
remember some engines relies on air cooling so oil flow alone does a significant amount of internal heat absorption and heat transfer.
a separate oil cooler with powered fans, and a shroud,
has a very noticeable effect on reducing oil temps, and as a result engine operational temps.



dual electric fans with a matched fan shroud, with a properly sized aluminum radiator, are generally the more efficient route to use in a cooling system

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