I spent last week in Moab and my transmission temp was reading high 220-255 the entire time we were wheeling, here is the background. I have looked at a ton of posts where after the external cooler install they never saw over 200 even on a scanguage which tends to read hot. All I can conclude is maybe the bumper is blocking too much airflow, but the cooler is mounted above the top of the bumper. Any input would be great, maybe these temps aren't as bad as I think for mountain driving?

-99 4runner 3.4 33's 4.3 gears
-Ambient temps were never over 80 degrees outside
-High temps typically occurred on long uphill climbs heating from 210-250 in 1st gear within 5-10 minutes.
-Reading temps on a scanguageII
-B&M 70264 Installed right against condenser, with input on top and output on bottom. I reconnected the radiator cooler inline when down there to try to help, but it didn't help much at all.

-Taurus fan installed in stock fan shroud, completely sealed so air is being drawn through. Fan was on high every time which is more than stock fans move.

-When transmission temp was getting that hot, coolant temp never passed 210 degrees.

-There is good flow through the lines, I pulled them off to verify the return line was flowing.

 

Do the coolant and transmission sensors read the same when you start up the car from cold?

 

I never thought of that no they do not. Lowest I've ever seen the tranny output as a temp is 105 degrees at start up. The coolant temp is typically 20 degrees above the air temp at start up. Today it was 105 and 74 degrees respectively. Do other people get better readings than that?

I have a thermal imaging camera at work I'm going to take a picture of the under hood temps and see what the temps really are.

 

Do you still have the mechanical fan in place?

Also I would get a real gauge for testing the transmission temp before getting too worried.

 

I know for a fact that my coolant sensor reads exactly as ambient, as it should, when engine is cold. So your sensor is probably mis-calibrated. You can just figure out an offset when the engine cold, but to be more sure, might be worth taking a few readings over the temperature range.

 

The sensor in the tranny may not be working correctly therefore incorrectly reading the temp of the ATF.

Have you ever read the ATF temp via the Scangauge with the stock fan clutch operating?

 

Unfortunately I didn't get the scan gauge until after I put in the electric fan