Transmission Cooler Thermostat Partially Stuck Open..

Here’s an interesting thing that happened to my 2018 SR5. I tow a NoBo 20',16.8 from Forest River at about 3800# loaded. I live in upstate NY and frequent the Adirondacks for camping. It’s not the Rockies but some of the hills get high real fast. I never saw the Taco ever exceed 225°F on the scangauge for either the pan or the TC while pulling the trailer. The truck has about 44K so I decided to go to my trusty garage and have them flush the fluid. When I got the truck back, I was climbing to about 214°F just going around town - something the truck had never done before. At first, we though the flush dislodges something and it got trapped in the cooling line. The guys had me bring it back and they checked it over and didn’t find any issues. I took it back and it still climbed very rapidly around town. So, back it went. This time they changed the oil cooler that connects to the radiator and then onto the hex at the grill. (Toyota part: 224100-4240). After this change-out the tstat opens and closes right at 185°. What the tech is thinking is that when the truck was NEW the original tstat in the cooler was actually sticking open a little (much like we pin it for hauling) giving me the impression of it always running cooler. Then after flushing, it jammed it shut and caused the faster rising temps. The new cooler component (manufactured in 2021) while pulling the trailer keeps the temp right at 204°F . The tech mentioned that he has heard that some of the thermostats in the cooler can get faulty. Another reason to flush the tranny when required.

 

Welcome to the forum. Thanks for the information, I’ll file it for later.

 

Welcome and Thanks!
It's always great to learn how a particular problem was diagnosed and then how the repair was developed.
EDIT: It also great when an OP posts a question, some Back'n'forth occurs, and then the collective finds the solution, AND IT GETS POSTED. Wish more did that.

 

Welcome to the forum