Trans temp: How hot is too hot?

99wranglersport · May 20, 2018

On my 06 LJ Rubicon with an automatic and 35 inch tires, I have a Super Chips trail dash and with normal driving on the highway or slowly driving backroads the warning pops up the that the trans temp is over 220 degrees. The engine temp is normal. It has the original trans cooler in the radiator. Usually if the cooler is in the radiator and the trans temp is high it makes the engine temp high also. So my question is how high is too high on trans temp? Do I need to add an auxiliary trans cooler? Is the trail dash just being cautious? If I didn't have the trail dash hooked up I wouldn't even know about the temp. It seems to shift fine and doesn't slip. Let me know your thoughts or advice. Thanks.

creepycrawly · May 20, 2018

The short is yes, add a cooler. If you google trans temp charts, you will see the guidelines for longevity at various temperatures. The question though then becomes where is the temperature sensor located. The other big issue though is that the 42RLE is notoriously bad about short lifespan when ran hot. It also has a really tall overdrive. Depending on what gears you have, the 2 best things you can do for it are add a cooler and turn the overdrive off unless you are on the highway.

My 05 LJ has 4.56's and I absolutely wish they were 4.88's or 5.13's with that stupid auto even on the 35's.

bbone · May 20, 2018

JohnG never had a trans temp monitor. He would say "you can feel when one is getting too hot.." Obviously in a buggy its easier than a full body rig but I was always under the rule of anything over 230/250 is breaking down the oil pretty fast. Ive gotten hot a few times and the oil didn't look burnt when inspected. Get a cooler...biggest one that you can fit and check it off your list of things not to worry about.