Transcooler and Thermostat install on 2021 4runner

Wanted to share info here, in case anyone wanted to do a similar upgrade to their 4runner and to provide any cautions so it wont happen to anyone else.

Long story short (as short as i can make it) wanted to prep my 4runner to tow a 3K trailer. So i opted for stiffer springs in the rear (dobinsons) and also wanted to install a thermostat. When i called a local shop, they recommended to install this thermostat (pictured below) so it will bypass the transcooler in the winter months and will open when it gets hot, to help cool the transmission. Sounded like a great recommendation initially.

1 week after install, the thermostat started to leak. brought it in, they added some high temp sealant to the fittings that go into the thermostat. Drove it back home, after another week, it started to leak again. So this time they replaced the thermostat and added more high temp sealant to the fittings. All looked well until i took a trip to Vegas (a month later). When i got to Vegas, the entire thermostat began leaking yet again. Had my brothers shop take out the thermostat all together. The fittings suck..and im sure if i took the time and money to upgrade the fittings, i could possibly get it to work without any leaks. Issue is, i was done spending Uber money taking the 4runner to the shop on a constant basis. Once i got back to Utah..i then noticed another leak...this time possibly from one of the hoses, or maybe even the transcooler itself.

The shop said they will provide a refund for the thermostat, but i doubt they will refund me for the labor. and this thermostat is really inexpensive (maybe 40 bucks at most). Now i am spending money on another shop to go over the entire transcooler install (thats closer to my house) and see what is or isnt leaking and get it fixed once and for all. If the transcooler is leaking, i am taking it out and tossing it across the parking lot and going back to OEM eveything lol

I think i spent close to 2 grand total for all this crap, and its seeming like the worst idea i ever made. In stock form, this 4runner is bullet proof and it still towed the trailer no issues without the transcooler. I dont think its necessary to even install. Just change fluid if you are hauling frequently. At times it seems like a great idea to mod this thing, but honestly..from factory these things are bullet proof. Replacing suspension is probably all i would recommend or do with the 4runner. all else, leave it alone and if you need to tow or haul beyond its capabilities, get a tundra.

 

For years I ran hydraulic power supplies in the lab, pressures upwards of 10Kpsi at 10-25 GPM and NEVER used any kind of 'putty' on the port threads. If not AN style fittings or Swagelok we would use Teflon Tape for (temporary) threaded NPT unions. Leaks can also occur from over-torquing this style of thread (tapered - NPT) by causing cracking of the female side of the junction. By the looks of that Derale thermostat I'd say its a cast part, that kind of material can more readily develop fractures within the metal alloy than a machined - billet design. Since (if) you have that part out I'd recommend that you take a very close look at the thermostat' surfaces (radially) around each of the threaded holes and look for tiny hairline fracture(s), replacement of the thermostat housing is the only resolution if there are any fractures present.

 

Welcome

 

Been running a Hayden trans cooler for about 3 years now. Granted I am in Socal so I do not need a thermostat but never had an issue or leaks. I also run a Durale power steering cooler, just to remove the low hanging hard lines with my front bumper. Installed for over a year now and knock on wood, no issues.

 

I wanted to show a good investment for engine and transmission cooling. You won't ever have to worry about the factory plastic aluminum leaking either. You can install a auxiliary transmission cooler then while it's easier. Not really necessary, but I know how you feel. I'm used to driving Mopars with new, bad transmission designs except the old ones. I wish I had wasted my money on this instead of other items that did nothing. I keep mine 4runners and they will usually need replacing around 300k or so anyway. Bigger throttle body not that good. Aftermarket intakes not that good. The AFe looks like the best design for intakes. It has ram air attachment that plugs into the box in front and lays on the radiator cowl collecting air from front of the hood as option. Conical dry filter, inspection window, more direct air route between box and TB. Anyway, there you are if it helps.

 

I am also running the CSF radiator, not sure I saw any improvement with temps. I think it does add a bit more volume (dont quote me on that) but I would save your money on that "upgrade". I constantly monitor water, trans, torque converter temps on my scan gauge

 

Did you monitor trans temps to see if you even needed a cooler? Many of us have and found that with smaller trailers (mine is 3600 lbs) in 95 deg weather up some good hills staying in 4th the temp only rises 5-10 deg and stays at it's minimum temp (regulated by the coolant temp and internal thermostat) about 192-195 most of the time. If you downshift or have to use 2nd or 3rd gear the trans temp will climb but the total time it's up to 230-240 is usually very short so has little effect on the fluid. So you may not even need one.

The main point being no matter how good you or your techs are, adding a trans cooler introduces more potential points of failure and leaks to an already extremely reliable platform.

 

Welcome

 

Welcome from Wisconsin!