temp gauges coolant temps and infrared thermometers

[grumpyvette]

in most cases I see where guys are worried about engine temps its due to either realistic indications like the engine obviously IS over heating, like its "puking coolant " steam under the hood", coolant "leaks etc" or sometimes its just a gauge that reads higher than the owner thinks it should.
obviously you need to verify coolant and oil levels as a first step and verify the actual temperatures
I SEE MORE DEFECTIVE COOLANT TEMP GAUGES,OIL TEMP GAUGES and ENGINE TEMPERATURE SENSORS THAN OTHER TYPE OF GAUGE
well if the engines showing no indications other than the gauge reading high, Id strongly suggest you think about the potential of a defective sensor or gauge before running around chasing an over heating issue that may not even exist.

http://www.professionalequipment.com/ex ... ermometer/
in a properly functioning EFI system theres a constant flow of fuel thru the injectors and back to the fuel tank thru the fuel presure regulator assuring the fuel in the fuel rails feeding the injectors remains fairly cool in relation to what engine compartment temps are, (you can verify that with an ACCURATE infrared temp gun)

your engine coolant normally tends to run in a temp range of about 15F-20F under your oil temp range and in most cases that coolant temp should be in the 180F-220F range with about 180F-200F being a great optimum range, as oil temps in the 190f-220f range are about optimum also on most engines, if your oil temp gauge reads lets say 210f-220F after the engines fully warmed up and your not running an auxiliary oil cooler you can reasonably assume the coolant temps are lower! (usually 10F-20F lower)
now if you suspect the coolant temp gauge may be defective checking with a second temp gauge is advisable or if you have a reliable infrared temp gun you can point it at the intake near the t-stat which normally reads 5-10 degrees cooler than the actual engine coolant temps as coolant flows to the radiator. keep in mind cylinder head temps tend to be a bit hotter
having An infrared temp gun in your tool box can save you a lot of time locating a problem at times

as always a logical isolate and test procedure is the way to proceed, you either isolate the problem to some thing generating too much heat or a failure to rapidly and effectively transfer that heat from the engine to the outside air flow,or a faulty gauge and doing that can be done thru logical testing
just because the water pumps brand new does not mean its correct for the application and I suspect its not,theres reverse rotation water pumps for serpentine belt use and you might have the wrong water pump, or the gauge not the sensors defective , obviously an infrared temp gun could be useful here, oil temps generally run 15-20 degrees hotter than coolant temps and oil temps in the 240f-250f range would be a problem.
OBVIOUSLY youll want to verify your ignition advance curve, fuel air ratio and check for exhaust and vacuum leaks, if your ignition timing is not correct it can cause over heating and if the engine builder failed to get the bearing clearances , valve train clearances or ring gaps correct, or its tuned incorrectly like its running lean or has a vacuum leak, it will run hot.
when temp sensors don,t agree then ones obviously either measuring a different area with a different temp OR the sensor or gauge is defective, to find which is true youll need to verify with a reliable third measuring tool, like a quality IR temp gun, and measure the sensors with a multi meter

http://www.professionalequipment.com/ex ... ermometer/

as always a logical isolate and test procedure is the way to proceed

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it would be normal for the area between #6 and #4 to run a bit hotter than , the area between #4 and #2, if that area runs hotter its usually an indicator of a leaking head gasket
http://www.blockchek.com/index.htm
Sensor Outputs:
If your having issues with a temp gauge not reading correctly the first thing you need to find out is that you need to know the correct sensors ohms resistance value for a given heat level and what the gauge is expecting to see.,if the sensors providing the gauge with the wrong resistance the gauge will show the wrong temp indication, heres a typical sensor
Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
but its far from rare to find a sensor that has wildly different ohms values, at different temperatures, depending on the manufacturer and intended application, or to have a defective sensor that only randomly changes resistance,
an INFRARED TEMP GUN AND A MULTI METER CAN BE USED TO VERIFY SENSOR OUTPUT

 

[grumpyvette]

HEY GRUMPYVETTE??
MY Temp gauges disagree
I was having some AC issues with my car 1996 corvette, and I pulled the radiator and cleaned the condenser, now my temp gauges disagree. The digital temp reads about 20 degrees cooler than the analog gauge. Which one is correct, and what did I mess up when I took everything apart?


leon posted this bit of info
"Exhaust gas temperature (EGT) depends on combustion temperatures. The hotter the mixture burns inside the cylinder, the hotter it will be coming out. Theoretically, combustion temperatures are at a maximum at stoichiometric, but realistically the maximum occurs slightly rich from peak because of the dissociation of Oxygen from the combustion products (CO2, H2O). Why temperature drops when rich or lean is described by the energy released caused by the chemical reactions between the fuel and air. Too little fuel (lean) and there is less energy contained within and more heat is transferred to the cylinder walls (no fuel evaporation or boundary layer), thus the lower temperature when it burns. Too much fuel, and combustion efficiency drops thus generating less heat.

I know, this is not too detailed, but it gets the point across without involving too much technical jargon.

Of course, this all assumes MBT timing and stable combustion. You can also change exhaust temps by varying spark timing, arguably more so than by just varying AFR. EGT is increased when spark timing is retarded since you are giving the gasses in the cylinder less time to cool off before the exhaust valve opens. "
both the rate of the ignition advance and where the ignition advance started at can be just as important as the total ignition advance.
theres several factors at work, but piston surface heat, quench and fuel octane are major factors in when detonation occurs
Most automotive engines use aluminium pistons that move in an iron cylinder. The average temperature of a piston crown in a gasoline engine during normal operation is typically about 300 °C (570 °F)
The self ignition temperature of gasoline mixed with air , in about a 14:1 ratio is about 495° F,, but it takes time for the incoming charge to absorb heat, theres much more time at lower rpms, at 3000rpm theres about 25 intake strokes per second, but at idle or 1000rpm theres three times longer for the fuel air mix in each compressing cylinder to absorb heat , the ignition advance is normally not needed past about 3200rpm because both increasing cylinder turbulence and rapid compression, plus increased heat levels speed up the combustion process.
it takes about 30-40 thousands of a second to have a cylinder burn during low rpm operation, leaving time for compressed gases to self ignite from absorbed heat and pressure building in the area near the spark plugs ignition point, at higher rpms theres far less time for the fuel to absorb heat and self ignite before the far more turbulent and rapid burn reaches the trapped gases, effectively making self ignition or detonation a non-issue.
BTW this is one area where a IR temp gun can be useful, if both the ignition timing and fuel air ratio are reasonably near ideal exhaust manifolds tend to run in the 500f-670f range depending of course on displacement,compression and cam timing, a retarded ignition timing allows part of the burn sequence to occur while the exhaust gases exit the cylinder, resulting in glowing headers

the dotted line shows pressure and heat during detonation
the solid line shows normal combustion pressure and heat
the inconsistent lines indicate missing or partial ignition

hypothetically the ping or detonation your hearing could be the result of not the total timing but an ignition advance coming in to rapidly that over heats the cylinder to the point that even after the ignition advance is correct for the 3000rpm plus cylinder speed the cylinders already heated to the point it continues to detonate due to piston surface temps raised earlier in the pistons acceleration to 3000 plus rpm, so the cylinder temp just continues to increase further increasing the tendency to detonate, it doesn,t take a huge increase in cylinder heat to cause a cascade effect,pushing the conditions into detonation, if the compression and fuel octane levels are very close to reaching detonation to start with

related info

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when temp sensors don,t agree then ones obviously either measuring a different area with a different temp OR the sensor or gauge is defective, to find which is true youll need to verify with a reliable third measuring tool, like a quality IR temp gun, and measure the sensors with a muliti meter

http://www.professionalequipment.com/ex ... ermometer/

having a good cross check tool like a quality IR temp gun, and a decent multi meter, sure helps find the truth as far as a defective gauge or sensor

always drop back to the basics!
any time your car starts acting out of character,
you always need to do basic tests on the basic mechanical function, electrical voltage, fuses, and grounds and gasket integrity , before looking for more exotic causes for problems, for those tests a shop manual, an infrared temp gun, an a/f meter, reading spark plugs, a voltage & ohms meter, timing light, and vacuum gauge and and for anyone reading this,use the darn, infrared temp gun, and using your head, rather than swapping components at random, can be used to isolate the cause. I constantly find its the basic stuff that gets over looked, things like just gaping plugs,setting the timing, adjusting carbs,and adjusting the valves, looking for leaks, and verifying pressure, coolant and oil levels, seems to get ignored

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http://www.aa1car.com/library/electric_cooling_fan.htm

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[grumpyvette]

"HEY GRUMPYVETTE? What would cause temperature differences on header primaries"


first keep in mind theres always going to be some difference in engine temps between cylinders and theres usually a strong tendency for the front cylinders to run a bit cooler because the coolant from the water pump feeds the lower front of the block and air flow from the fans generally has a good deal more air flow cooling the front cylinders, as both the coolant in the block and the air flow around the outer surface of the block move to the rear they have absorbed heat so they don,t cool quite as efficiently as both move to the rear of the engine.
theres also the fact that the fuel/air ratio and ignition advance don,t tend to be EXACTLY the same for all cylinders, and leaner fuel air ratios and a slightly retarded ignition will both tend to raise exhaust gas temperatures. now the difference in temps in a properly cooled and well tuned engine will not be huge but its rare for all the cylinders to be reading with-in lets say 20-F degrees, of each other.
you can tell a great deal by reading spark plugs and using a HIGH QUALITY, INFRARED TEMP GUN.
This is one area where MPFI has always had advantages, as the cylinder to cylinder fuel/air ratio tends to be a bit more consistent
youll find a hour or so reading thru the links and sub links, on this site in the threads, will provide a great wealth of related info and incite into related factors, or the function or testing of sensors, that you may not currently be thinking about, or things that you might not think that are related to your issue that PROBABLY ARE
RELATED INFO
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[grumpyvette]

I got a good deal on a rebuilt sbc. The rebuilds I've done in the past didn't run hot, but this one I got wants to stay around 220 to 230 all the time, whether it is idling or driving at any speed. Even when I turn the heater on full it wants to stay in the 220 to 230 range. I've tried 2 different thermostats, and 2 different sensors with the factory gauge, and an aftermarket gauge. The upper hose feels hot around 195-200* (they were stock 195* thermostats). So I'm convinced the engine really is running that hot and it isn't the gauge or thermostat. Should I be concerned?

Details are 1990 Chevy C1500 with a 305 and TBI. The only non-stock items are that the cylinders were bored .030 over and they are hyper-eutectic pistons. I know this is rather far from being a performance application and the truck section here for this truck has some knowledgeable and helpful people, but I'm asking here in performance because there are a lot more rebuilders who frequent this section. I don't know if this is just a break-in issue or if there is an engine problem.

BTW the radiator and water pump are new.

have you tested the coolant temp with an infrared temp gun, most auto parts stores have one they let you use in the parking lot to check, point it at your t-stat housing, then the water pump casting , with the engine idling, then at the oil pan, sump, write down the readings after the engines been running, and driven,around for at least 6-7 minutes so its fully up to operational temp.
as always a logical isolate and test procedure is the way to proceed, you either isolate the problem to some thing generating too much heat or a failure to rapidly and effectively transfer that heat from the engine to the outside air flow,or a faulty gauge, and doing that can be done thru logical testing
just because the water pumps brand new does not mean its correct for the application and I suspect its not,there are reverse rotation water pumps for serpentine belt use,and standard rotation water pumps for v-belt use and you might have the wrong water pump, or one rebuilt with the wrong internal components or the temp gauge not the sensors defective , obviously an infrared temp gun could be useful here, oil temps generally run 15-20 degrees hotter than coolant temps and oil temps in the 240f-250f range would be a problem.
OBVIOUSLY youll want to verify your ignition advance curve, fuel air ratio and check for exhaust and vacuum leaks, if your ignition timing is not correct it can cause over heating and if the engine builder failed to get the bearing clearances , valve train clearances or ring gaps correct, or its tuned incorrectly like its running lean or has a vacuum leak, it will run hot.
when temp sensors don,t agree then ones obviously either measuring a different area with a different temp OR the sensor or gauge is defective, to find which is true youll need to verify with a reliable third measuring tool, like a quality IR temp gun, and measure the sensors with a muliti meter.
theres also a slim potential of a leaking head gasket , cracked head or block, so don,t assume that just because the engines a fresh rebuild its flawless, just test and isolate until you locate the cause and don,t assume a darn thing, pull the plugs and look at them for clues, look for bubbles in the radiator , theres test kits NAPA SELLS that DETECT exhaust gases in coolant.
like I stated earlier theres a dozen reasons it could be running hot ranging from simple stuff like the timing curves wrong,cam timing installed a bit off, its running lean, or theres a vacuum leak, too more complex, like tight bearing clearances to, tight ring end gaps too a leaking head gasket,or a partly clogged coolant passage in the block,a cracked head, tight valve guides,etc. so,isolate and test in a logical manor, ID certainly start with a quart of marvel mystery oil added in the engine to reduce friction and help soak oil into the metal micro cracks and checking for loose fan belts,make sure theres a strong flow of coolant thru the radiator with the t-stat temporarily removed, so you know the water pump works as designed , verify the fans installed correctly, and do a leaky head gasket check test .
once you locate the problem you might want to correct that, or you might just want to put the engine on an engine stand , pull it apart , mic all the specs and carefully reassemble it so YOU know what YOUR dealing with rather that being forced to GUESS what some one else did with what might be as far as you know a random assortment of miss matched components that were not properly clearanced or fitted together, at times when your dealing with a new engine you just purchased this is a rather painful but in the long run much cheaper and much better alternative



infrared thermometers are a very useful tool to track down issues with tuning, or mal functioning sensors , without verified facts your guessing.
this is the most consistently accurate I.R temp gun I've used for testing[/img]

http://www.testequipmentdepot.com/e...1100200223789&utm_content=All Extech Products
INFRARED TEMP GUN

http://www.aa1car.com/library/gasket_failure.htm

http://garage.grumpysperformance.com/index.php?threads/vacuum-gauge-help.9453/#post-34623

http://www.hotrod.com/articles/innovate-air-fuel-ratio-meter/

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GLOWING RED HEADERS



GLOWING RED HEADERS

think it through ...thats USUALLY the result of a good deal more HEAT exiting the engine in the form of HOT exhaust gasses,exiting the cylinder and entering the headers..
hot exhaust gasses result from either overly lean fuel/air ratios
OR
a retarded ignition timing, that delays the burn of the compressed gases, and allows still burning fuel /air mix to exit the exhaust port.
OR
cam timing that is causing very effective cylinder scavenging that allows some of the fuel/air mix to enter the headers after passing through the cylinder , as inertia drags it out following the previous exhaust gases ,before the exhaust valve closes.
OR
very rarely miss firing injectors throwing excessive fuel
honestly a bit of basic engineering and thinking about a cause and effect relationship and a bit of testing can go a long way toward isolating a logical search for any problem.

 

[87vette81big]

An area to check also is the water pump.
The 1987-1995 Chevy GMC 305 & 350 TBI Uses a Reverse rotation water pump with stock pickup & Suburban bracketry & serpantine drive belt. Wrong water pump or built with the wrong standard rotation Pump impeller will cause Grief.
Lots made in China today. Often stock replacement in a bind you don't have a choice but to buy local parts stores offerings.
I have near Zero issues with NAPA Replacement parts.
If I do , they exchange immediate, No Hassles.

 

[philly]

pump cavitation is an issue at times if you like to rev the motor to the moon while the thermostat is still closed... even engines with coolant bypass systems built into the motor may not have enough flow to prevent it... could have a blown out water pump and not even know it.


hey grumpy, i heard this guy say once that he uses a laser temp gun to "tune" headers to read the same temps at all the primaries... he described denting the primaries to change their temp reading (i assume by slightly choking the gas flow at the point of the dent)? have you ever heard of this method? i cant recall when i heard it but it was sometime here in miami so since last september when i got back from the army.

 

[grumpyvette]

....

hey grumpy, i heard this guy say once that he uses a laser temp gun to "tune" headers to read the same temps at all the primaries... he described denting the primaries to change their temp reading (i assume by slightly choking the gas flow at the point of the dent)? have you ever heard of this method? i cant recall when i heard it but it was sometime here in miami so since last september when i got back from the army.

thanks!! I can always use a good chuckle

that logic's based on restricting a good flowing port so it equalizes with a less effective port is about like curing a bad limp in your left leg , you have from a sprained knee, by taking your 45acp caliber pistol out of you belt and blowing your little toe clean off on your right foot,with a carefully placed shot, so you tend too walk the same way with both feet, so now your equally screwed up! on both sides

I guess the concept of equalizing the fuel air ratios, between cylinders , thru staggered jetting ,plenum spacers and power valves ,use of Annular vs. Down Leg boosters , or programing different pulse duration on injectors , or intake runner porting or staggering rocker ratios, and porting intake plenums ,, or changing stack lengths on stack type injection, just never entered the guys mind

 

[philly]

....

hey grumpy, i heard this guy say once that he uses a laser temp gun to "tune" headers to read the same temps at all the primaries... he described denting the primaries to change their temp reading (i assume by slightly choking the gas flow at the point of the dent)? have you ever heard of this method? i cant recall when i heard it but it was sometime here in miami so since last september when i got back from the army.

thanks!! I can always use a good chuckle

that logic's based on restricting a good flowing port so it equalizes with a less effective port is about like curing a bad limp in your left leg , you have from a sprained knee, by taking your 45acp caliber pistol out of you belt and blowing your little toe clean off on your right foot,with a carefully placed shot, so you tend too walk the same way with both feet, so now your equally screwed up! on both sides

I guess the concept of equalizing the fuel air ratios, between cylinders , thru staggered jetting ,plenum spacers and power valves ,use of Annular vs. Down Leg boosters , or programing different pulse duration on injectors , or intake runner porting or staggering rocker ratios, and porting intake plenums ,, or changing stack lengths on stack type injection, just never entered the guys mind

thats what i thought... i was picking up parts and this guy was describing the process to my buddy who owns the parts place, and i only heard the jist of the conversation but i was left thinking wtf is this guy talking about? glad you could put that to bed for me, it had been rolling around in my head for a while

 

[grumpyvette]

I found an infrared thermometer. Most of both of the heads read around 220*, but between #2 and #4 it reads about 250*. What does that mean?

I'd think its looking a bit more like a leaking head gasket, but ID want to do more testing, keep in mind the two exhaust ports exit in the center of the cylinder head on a chevy so that area naturally runs a bit hotter , what do the spark plugs, in all the cylinders look like ?
and Id look for coolant in the oil and get a exhaust gas test kit from napa

http://www.professionalequipment.com/ex ... ermometer/
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.
having An infrared temp gun in your tool box can save you a lot of time locating a problem at times
http://www.harborfreight.com/non-contac ... -8905.html

it would be normal for the area between #6 and #4 to run a bit hotter than , the area between #4 and #2, if that area runs hotter its usually an indicator of a leaking head gasket
http://www.blockchek.com/index.htm


OBVIOUSLY you need to verify TDC on the damper and timing tabs are correct and the ignition timing is correct
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[87vette81big]

....

hey grumpy, i heard this guy say once that he uses a laser temp gun to "tune" headers to read the same temps at all the primaries... he described denting the primaries to change their temp reading (i assume by slightly choking the gas flow at the point of the dent)? have you ever heard of this method? i cant recall when i heard it but it was sometime here in miami so since last september when i got back from the army.

thanks!! I can always use a good chuckle

that logic's based on restricting a good flowing port so it equalizes with a less effective port is about like curing a bad limp in your left leg , you have from a sprained knee, by taking your 45acp caliber pistol out of you belt and blowing your little toe clean off on your right foot,with a carefully placed shot, so you tend too walk the same way with both feet, so now your equally screwed up! on both sides

I guess the concept of equalizing the fuel air ratios, between cylinders , thru staggered jetting ,plenum spacers and power valves ,use of Annular vs. Down Leg boosters , or programing different pulse duration on injectors , or intake runner porting or staggering rocker ratios, and porting intake plenums ,, or changing stack lengths on stack type injection, just never entered the guys mind

You made Smile Ear to Ear Grumpy.
Thanks.
:lol: