I have with an infared thermometer which is why I put the stock cooler back in the loop. The fluid coming out of the transmission is hotter than the cool side radiator tank. Fluid temps are around 190-210°F on the trans outlet and my cold side radiator tank runs around 140-160°F tops. The engine runs around 178°F going down the road. At idle it will warm up a bit due to the 25% underdrive pulleys but it stays under 200°F on the hottest days. Even at idle the 170°F switch on the electric fan seldom turns the fab on. I put it on the return side of the cooler which helps keep the temperature more consistent.

 

I'll just leave this right year. Some people don't know who Fast355 is.

https://www.performancetrucks.net/forums/foreign-performance-discussion-116/400-rwhp-titan-making-529977/page11/

 

You can think what you want but the transmission cooler in the radiator is very effective at helping keep trans temps low under load. Unfortunately the same cannot be said of the torque converter temps under high load, low speed pulling. A factory converter and 4.56 gears fixed the high trans temps for me while towing. With the high stall and 3.73s I managed to get the fluid cooler output from the converter so hot one day the lower metal line melted part of the fan shroud as well as the section of rubber hose entering the upper radiator. The in-pan temps never broke 200°F!!! I moved my temperature sending unit from the pan to the output port after. That is when I found the trans temps post converter with a loose unlocked high stall converter can reach 300°F on long hard, slow pulls. That day the in-pan temps never broke 190°F measured by the factory thermister. With the stock converter and deeper gears to take load off the engine and trans, now the output temps on mine run in the 190-210°F range. On the same section of windy, uphill road I was pulling in 1st unlocked at 4,500 rpm I now tow up in 2nd lock at 3,500. Speed limit is 45 mph on this section of road and 40-45 mph is the fastest I would want to go through most of it anyway. Also just so happens to be about 6 miles of near constant 6-8% uphill grade. Also worth mentioning many people will not need the cooling capacity the factory cooler adds but those that tow should think twice before removing it especially with a high stall that spends any time unlocked.

 

Good post.

 

That's 7 minutes of my life I'm not getting back...

 

Sounds like the header is touching the trans line for it to rise up 30* sitting still in park.
I would check it