Can a transmission run too cold?

[Mike_H]

Wanted to start a discussion about transmission coolers, specifically the Setrab that @mrblaine uses. I know the a lot of guys will just copy him and run what he runs, because of his experience and knowledge. However, He builds jeeps to run in the desert and climb mountains. I'm planning out an auto swap (42RLE) and looking into coolers. I think I'm going to stick with the Setrab proline series, because of the fit, but I'm contemplating going with a smaller core. The average highs in Michigan for the summer run around 80 degrees and we're pretty flat. We have some hills, but the whole state only has about 1500 feet of elevation change from low to high point.

I do get into mud and sand, so for some brief periods there will be some high slip usage...but will I regret not buying "extra" cooling capacity, or if I get the big cooler, will I be overcooling the transmission and it will never come up to operating temp (if there is such a thing)?

 

[Obi-Wan]

Unlike an internal combustion engine that needs to run "hot" in order to maximize efficiency, transmissions really like staying cool (to a point).

but will I regret not buying "extra" cooling capacity, or if I get the big cooler, will I be overcooling the transmission and it will never come up to operating temp (if there is such a thing)?

Keep in mind that an engine has water AND oil to help keep temps managed, and a transmission only has oil to do so. A good rule of thumb is to keep your trans temps around 170°-180°F. To cold of a transmission fluid will greatly decrease its overall efficiency, but shouldn't hurt anything internally.

Since you're not planning on towing, hauling large loads, and occasionally going off road, a small cooler like this should be more than effective.

 

[mrblaine]

Wanted to start a discussion about transmission coolers, specifically the Setrab that @mrblaine uses. I know the a lot of guys will just copy him and run what he runs, because of his experience and knowledge. However, He builds jeeps to run in the desert and climb mountains. I'm planning out an auto swap (42RLE) and looking into coolers. I think I'm going to stick with the Setrab proline series, because of the fit, but I'm contemplating going with a thinner core. The average highs in Michigan for the summer run around 80 degrees and we're pretty flat. We have some hills, but the whole state only has about 1500 feet of elevation change from low to high point.

I do get into mud and sand, so for some brief periods there will be some high slip usage...but will I regret not buying "extra" cooling capacity, or if I get the big cooler, will I be overcooling the transmission and it will never come up to operating temp (if there is such a thing)?

3 things for you.
1- no one should blindly copy anything without knowing why.
2- average temps in our wheeling season in JV at night are rarely above freezing.
3- excess capacity can easily be mitigated with the addition of a thermostatic control valve or thermal bypass valve. I'd look for one in the 170 degree range, it will bypass fluid back into the trans until it gets up to 170, then it opens and sends oil through the cooler and if that overcools it, it reverts back to bypass.