Choosing An Engine Oil Cooler Or Transmission Fluid Cooler


New Member
Hi there,

So I'm looking for guidance regarding how to choose an engine oil cooler. I don't want to get one too small or I guess too large.

I looked through the threads in part of the forum but did not find anything that popped out at me that I could use to help me.

Any guidance or references (not necessarily vehicle specific) would be greatly appreciated. I figure perhaps others could find answers to my question useful too.

Here's my situation:
Vehicle: 1999 Blazer, 143,000 miles
Drive-train: AT, 4wd, rear axle 3.73:1 (16,000 miles on recently rebuilt transmission with extra cooler installed)
Curb weight: 4,400 lbs
Intended Use: Pulling 2,200 lbs of boat and trailer up steep grades in Pacific Northwest. (e.g. 1,700' in 6 miles at US 95 at Lewiston Idaho, 1,900' in 10 miles at I-90 at Vantage WA, Snoqualmie pass WA on I-90)
Planned modifications: New radiator with core twice the depth compared to OEM (2" vs. 1")
Problem: Whereas the OEM radiator has a built-in oil cooler like for the automatic transmission fluid, the new replacement radiator will not have an integral oil-cooler.
Need: Advice for sizing a dedicated air-cooled oil-cooler.

Thanks in advance!


solid fixture here in the forum
I think it would be BEST To use an OEM Style replacement radiator.
I have a 1997 Chevy Blazer with a blown up 4.3 LITER V6. It's been dead since late 2011. Sits outside on my farm..
It was nice to have driving around and in inclement bad weather. Little Truck SUV would go through alot of rough roads and some hard off-road.
The Engine only has 4 main bearings.
It's a 305 Chevy V8 with 2 cylinders cutoff.
But the Old Buick V6 engine 3.8 LITER was superior that only lives on with the Buick Grand National Guys. Based off the really old Buick 350 V8.

Towing a heavy load and an S10 Blazer Long distance I don't know.
Asking for trouble perhaps maybe.
Got a 1999 Chevy Tahoe 4x4 I drive daily.
I rebuilt Blueprinted the 4L60E trans last year. I put Racing Alto Red Eagle Frictions and Like me steels in it and All the usual race tricks done to a Corvette 700R4 done in 2010.
Tahoe does good towing with its VOTECH 350 Chevy V8. Lots of towing power and never gets hot.


solid fixture here in the forum
There is not much room Under the hood of an S10 Blazer.
I know that.
Typical Road Race oil coolers and Teflon AN Lines and Steel fittings will cost at least $600 +.
Need to be #10 AN Lines at least.


The Grumpy Grease Monkey mechanical engineer.
Staff member
read these links ... Code=guide ... an-coolers

# Small compact cars, No towing Coolers with GVW ratings of 10,000 to 16,000 lbs.

Mid-size cars, Light towing
# Coolers with GVW ratings of 14,000 to 18,000 lbs.

Mid-size trucks & full size cars
Towing up to 5,000 lbs.
# Coolers with GVW ratings of 18,000 to 24,000 lbs.
Pickup Trucks, SUV's
# Towing up to 7,500 lbs. Coolers with GVW ratings of 22,000 to 26,000 lbs.

HD Trucks, Motor homes
Towing up to 10,000 lbs.
# Coolers with GVW ratings of 22,000 to 30,000 lbs.

Super Duty trucks
Large Motor homes
# Coolers with GVW ratings of 28,000 lbs. and UP

this thread has some useful info

one question that always comes up, is the ideal, size and length of the fluid transmission lines required,
too feed and return hot oil from remote mounted oil coolers and transmission fluid coolers, the simple answer, visit a local professional hydraulic supply shop after taking careful measurements and verifying the type of fittings, thread types used etc.
I would strongly suggest you select, and ask too have fabricated,
(after taking careful measurements and verifying the connection fitting type and threads etc.) high temp ,high pressure ,lines, AN#8-1/2" lines designed to handle 250F temps and 350 PSI. MINIMUM

keep in mind most performance cars with an auto transmission and a higher rpm stall converter, will need an auxiliary trans fluid cooler, Id strongly suggest you find one with an electric fan and 1/2" or AN#8 line size as you'll want to allow a minimum of 2 -3 gallons a minute trans fluid flow rate.
engine oil coolers , TRANSMISSION FLUID COOLERS and remote mounted engine oil coolers with remote filters, also benefit from use of a MINIMUM of a AN#8/1/2" inside diameter fluid transmission line .

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


keep in mind oil does almost all the initial engine cooling so adding a larger efficient oil cooler with a fan
, and as large an oil pan as clearances allow goes a long way toward reducing engine temps,
you certainly will see a difference if a properly sized and installed oil cooler is used.


you don,t need something this large in most cases

something like this makes a noticeable improvement

I recently had a friend ask if adding a trans fluid cooler like this might be a good idea?

$571 seems rather over priced

while the heat sink style pictured above, $182 seems far more reasonable
certainly may help, reduce trans fluid or oil temps,

it has far less ability to rapidly and constantly transfer excess heat out of the fluid ,to the outside air flow,
than something like the fan equipped radiator style fluid coolers linked below


$262 ??
flx-600029_mh_xl.jpg $188

remember to accurately measure the area you intend to install any oil cooler,
and leave lots of room for the connecting high pressure oil feed & return lines and access to connect them.


your main issue as is almost universally the case is finding a place to mount the fluid cooler that allows air flow and reasonably easy access,
don,t forget the trans fluid or engine oil lines and fittings will need access and room for the lines,
ID strongly suggest AN#8 or 1/2" line size and a cooler with a powered fan

Ive used this several times, but its not going to easily fit most cars, so step one is finding and measuring a location to mount it








Last edited:


The Grumpy Grease Monkey mechanical engineer.
Staff member




I've tested water wetter in several engines, its always resulted in at least a few degrees lower coolant temperatures, if you really want to reduce engine temps install a decent fan equipped oil cooler designed for a 24,000 lb truck with AN #8 line size, and ideally have a radiator with at least 2 square inches of frontal area per hp.
and yes youll rapidly find you require a larger radiator or one thats several inches thicker for greater surface area.
Last edited: