Transmission coolers

[booster]

Over the years there have been a number of discussions of transmissions running hotter than they should and aftermarket trans oil coolers to help out the situation.


An item that always comes up is the problem over over cooling the transmission in cold weather and all the ways (most of which don't work really well) to eliminate the over cooling.


Our 07 Chevy with a 6.0 engine and 4 speed automatic is one that would overheat and one of the things done to fight that was the addition of two big trans oil coolers that are not through the radiator for reheating to help prevent overcooling. What I did do was put an oil temp thermostat in the transmission cooling line so that in cold weather most of the oil is kept from going through the coolers.


Our van really never sees under freezing and is stored in a heated shop, so even in Minnesota we didn't get a very good test on cold performance.


But the last couple of days have had clear streets, as in no salt, but cold air near zero F. I needed testing on the remote alternator regulator charging so I went for a couple of test rides to the tests.


The temps were in the +4 to +8 degrees F, no cardboard in the radiator so just like summer setup. I was very surprised to find the transmission running in the 165 to 185 degrees all day, which is very near where it runs in the summer.



This certainly convinces me that using a thermostat in cooler lines and leaving them out of the radiator if the cooler has enough capacity is a really good way to go about handling big coolers and cold weather.


I certainly did not expect the results to be that good, so was totally surprised.

[Mtsailor]

Good information.Thanks.
A few questions. What was the thermostat that you used? Does it just cut off or reduce the flow, or does it bypass the coolers? are your two coolers plumbed in series with each other?

[booster]

Originally Posted by Mtsailor

Good information.Thanks.
A few questions. What was the thermostat that you used? Does it just cut off or reduce the flow, or does it bypass the coolers? are your two coolers plumbed in series with each other?

In the van with 6.0 and 4L80e trans I am using an Improved Racing full oil cooler sized thermostat with a 165* thermo pill in it, which runs about 10* warmer than that setpoint because the setpoint is where it starts to send more flow to the cooler.



https://www.improvedracing.com/high-...hermostat.html


Cooler thermostats are kind odd birds of the thermostat world, I think.


When cold at start they bypass about 90% of the flow per the specs, but those are mainly based on engine oil coolers that have higher flow than transmissions.


IR stat does it by using an H fitting with in and out for both flow to the cooler and back, plus a bypass between them that can be restricted by the thermal pill. That bypass is wide open at start so oil flow has an easier path through the bypass than through the restrictive coolers, warming the oil more because of nearly no cooling of the oil. As the oil heats up and gets thinner the bypass starts to close off and forces the oil to go through the coolers in progressively larger amounts as the restriction gets closed more. The design is this way, I think, so there is no way you can get a failure that would totally block the flow like you could if they just restricted one of the cooler lines. Transmissions need the full volume to operate without failing.


Our coolers are in series and the radiator cooler is not in use with them so they do all the trans cooling.


I also use an IR thermostat in my 96 Buick Roadmaster wagon with a 5.7 and 4l60e trans, but it runs through an add on cooler and the radiator. In that application I use there smaller thermostat and it also works well. The Buick weighs about 1/2 or what the van does, though.

[Mtsailor]

Thanks for that very thorough reply, Booster. That explains exactly what I wanted to know.