Is it safe to pin open Transmission thermostat?

Is there an official consensus to whether or not it would be harmful to keep the transmission thermostat pinned open for towing in the hot summer months? I live in the northeast so I’d probably take the pin back out for winter time.

My thought is the transmission also has the heater that exchanges heat with the hot engine coolant to bring it up to temp, and pinning the trans cooler thermostat open would just keep the temps in check in the 160-200 range which I think would be plenty suitable and not “too cold”. Even in extreme towing I’ve seen people say with it pinned open you may see the occasional 220.

I know there has been some debate in the past, but I don’t like the thermostat not opening until 200+ degrees. At that point it is already on its way to climbing rapidly if you're pulling a heavy load up a big hill with the TC unlocked. Has anyone had theirs pinned open for a long time with no negative effects? Thanks

 

I have not, but I would opine that it would be better not to pin it open. 200 degrees isn't a bad thing for synthetic transmission and oil temps; that's where it starts to boil off moisture that had condensed in the system from hot/cold cycles. (yes, I know the boiling point of water is 212F at sea level, but the temperature on the gauge is more of an average so you have hotter spots in the transmission). In my experience, I have not had issues with transmission temperature towing up to 10k on grade in 100F weather; I saw 226 once but rarely do I see over 213. The only time I see the trans temp climb is with the converter unlocked for long stretches, which usually only happens when I'm trying to milk things around 70 MPH with my enclosed and stay in 5th. With a headwind, it will unlock often so I either slow down a bit (not always the best option, but that's debatable), speed up to increase RPM's (again, not always the best option), or just knock it down to S4 and make sure the converter locks back up.

Pinning it open takes longer for the transmission to warm up, but also creates more temperature swings instead of narrower range of temperatures once at operating temp.

I guess I should also add that safe is kind of a relative term, so I don't think it will necessarily hurt the transmission, but I don't think it would help much either.

 

Pin it. I saw 255F in torque converter in 69F weather by just navigating back roads. Will be installing aux. cooler with no thermostat.

I drive my old Volvo with Aisin transmission, it has extra cooler added into heat exchanger's return line with no thermostat. It usually runs colder than 180 F, often colder than 130 F, for many years with no adverse side effects, other than a slightly worse MPG due to oil pump loss.

 

I definitely understand your thinking here. I’ve seen others bring that up about the condensation as well, but I’m not sure if it makes sense. The transmission and it’s related plumbing is a sealed system. This should prevent air from entering the system and therefore bringing moisture with it. Even if it did get hot enough to boil said moisture off, where could it escape to? It would just eventually cool down again and condense back into the fluid.

I may do a trial run with it pinned and just see how hot it gets in summer driving when I’m not even towing anything. If it’s consistently 170+ I don’t see the issue. I would only think it could help longevity. I know John from IPT who is pretty good with these had stated that it’s beneficial to keep the temp under 200 and had even recommended additional coolers. So much conflicting info on the subject.

 

In that case, I'd say try and and see what happens

 

Pinning seems pointless to me. The thermostat opens when it's supposed to, around 175-185 degrees, not sure the exact number. Once it's open, it's open. You don't get additional cooling from pinning it open all the time. You just mess with the warm up cycle for the trans fluid.

 

this.

it's not feasible for it to run cooler.

I run 62mph on the hwy a lot. I see 195 often. rarely higher.

pinning would make the oil heat up slower....but still max at the same #.

right?

 

It has a vent.

 

I think let it cycle, pretty sure that's how it worked when the trucks had coolers from the factory and the system seemed to be pretty solid and reliable. So, why fix what isn't broken?

 

If the thermostat was actually set for a more reasonable 190 I’d definitely leave it alone, but I read it’s upwards of 205-210+ that it opens, and watching my temps I believe that to be true. I agree that eventually even with it pinned it will reach a high temp eventually, but if you’re hitting the bottom of a huge hill towing with the fluid starting at 180 vs starting at 205 you’re ahead of the curve and it won’t reach the same peak temp as it otherwise would. I sort of believe they run the trans hotter not because it’s good for it, but because it lends to better fuel economy. Just like the 0w20 vs 5w30 argument.

 

Where is it located? And do you know if it is a one way check/pressure relief valve or if it is just open to the atmosphere?

 

I'll be your huckleberry.

I'll pin that b1tch open and see if my temps vary.

my data set will represent the slow steady S/C'd drivers. (I don't tow)

I'll give it a couple weeks. Houston is heating up.

 

Might find information on the location by researching the ARB vent relocte kit. I think the kit vents both differentials and the transmission all through one apparatus.

 

No point in pinning it open, your cooler is only going to cool as much as it is able too. The fluid temps will eventually stabilize if it’s opened or not. Keeping the thermostat open will just increase the time it takes to get to temp. To my understanding these transmissions don’t like to run cold, and I have noticed that myself during the colder months. Even during hard use in very hot weather, the cooler will drop hot fluid temps back to 185* right away. Your call but I don’t see the point.

 

The white cap in the middle of the picture, it's a breather like the one on the differentials.

 

Think I’m gonna do mine as well just to try it. Can’t hurt especially for a brief time I figure. I know others have done it.

 

Most importantly pin the damn thing open anytime doing any transmission service.

 

I agree, except why break what's already fixen?

 

It won’t hurt anything, it will just prolong the warming of the fluid. Whether or not that will hurt anything, I don’t know.

 

^^^^^

 

Ran mine pinned open initially for about a year until last Fall. Seems to be doing fine.

 

In other words, it should not allow air in but only pressure out I take it?

 

I believe it will allow air in/out and water as well if it gets high enough, which is the reason some people relocate the differential breathers to higher areas.

 

that’s the idea, but regardless of what is intended, air WILL find it way back in. It’s vacuum will stabilize eventually

 

All I know is I routinely see 205 to 225 towing my TT on the highway at 65. Guess I can pin it and check it on the next trip we have planned in July. If I’m towing it is basically never under 200 once up to temp. If I can have it hover a good bit below 200 then I think by the time I get to the top of big hills it will likely be at a lower max temp that it normally gets to with the thermostat doing it’s thing.

Agreed, but assuming I’m not fording rivers it should not allow water in at its current location.

 

Very interesting, I tow my travel trailer quiet a bit and at highway speeds almost never see it above 200 unless going up a steep grade and having to punch it. Even then, as soon and I let off, it drops down to 190ish like right now.

 

This is also monitoring the TC lockup and keeping it locked as often as I can. With the Supercharger greatly reducing the throttle position needed to maintain speed it is almost always locked except for pretty steep hills when I have it in S5 at 65. You’re aftermarket cooler may also be a higher BTU rating than the stock one that is part of the AC condenser.

 

Yeah, I wouldn't worry about it

 

you may have a point, I have the 20 row Setrab cooler. Even still your cooler should be more efficient than what you are stating. Possible flow issue I dunno?

 

From what I read pretty much everyone with the Factory trans cooler says theirs is the same when towing. I think it’s borderline undersized, which is all the more reason I don’t think pinning it in summer time is a huge issue. I don’t think it has the capacity to truly keep the temp of the fluid “too low” in summer time temps.