Pinned Trans Thermostat observations

Thanks! I agree with your climate dependent statement as well and pin mine open during the summer months too.

 

good points.

I would have a profoundly different tact if I lived up North.

and, given this Houston climate:
I don't stay "cool" demonstrably longer than I did before I pinned. >> I warm up to 125 fairly fast.
I'm still inquisitive as to the long hot Houston summers & what temp will I settle at.
I tend to like running a few degrees cooler than 195. for whatever reason.
If I was to ever run ~140 or lower, I would unpin, but I have yet to hit those conditions.

 

I’ve been getting into the 160s after it’s up to temp all winter despite living in the northeast. If I lived in Canada or Alaska perhaps it wouldn’t fly for me though.

 

Mine running unpinned runs around 195-200* at the converter doing 75mph on a 50* day. Sitting in traffic I see it go to 205-210 fairly easily but not much above that. I just started looking at pan temp yesterday to compare and it seems to be 20-30* cooler.

I know on a 40* morning it takes about 3-5 miles at 55mph to get the fluid warm enough for it to shift normally. Just as a point of reference.

 

5th gear is overdrive and is accessible at all temperatures. 6th gear and torque converter lockup are used when engine coolant reaches 140F or higher, even if transmission temperature is still under 100F. It also changes shifting stiffness at that engine temp threshold, allowing a tad more slip for a smoother shift.

Transmission fluid temp even unpinned doesn't reach 175F for a half hour or more after a cold start in cooler weather and maybe 15-20 minutes on a hot summer day if the truck isn't working hard. It warms up so much slower than engine coolant. Oftentimes when the engine gets to 185F the transmission is still lagging at 120F or so.

Too bad we don't have a servo and switch to push that pin on the fly. That would be sweet.

 

Dumb question how do you actually pin the thermostat open? I saw on the Tacoma forum it looks like an actual pin holding in a button looking thing, is that what it is? Is there a particular pin/method people are using? I know for engine coolant we can get cooler thermostats and physically replace it, but I am curious on how this is done for these transmissions.

 

Push the shaft in until it stops and using a 1.0 to 1.8 mm pin push it through the corresponding holes.
I can take a better pic tomorrow. I removed my warming puck and thermostat routed it straight to cooler. Over the winter it took 30 min to warm up and stayed 150-170deg on the south sound.

 

I will inject this tid-bit....

The location one needs to do this pinning operation is RIGHT NEXT to the exhaust.

and from practical knowledge that exhaust piece could possibly be damn hot.

this lesson cost me 15 cuss words.

 

I run mine pinned as well (and also a fan of Valvoline products).

I see 170-178 in hot weather.

And my 2021 4runner with the factory in-tank cooler does the exact same. I don't think an additional gear makes a difference.

my 4runner's temp trends are what convinced me to get the cooler.

I've noticed a few hard shifts. But I also had some hard shifts when new and no cooler installed either.

Fuel mileage is a wash*. It is already in lolwtf territory and I can afford it so it isn't a huge deal. but I didn't notice a drop of 2-3 mpg. If it dropped at all it was less than 1 mpg.

(*I did see an increase in fuel mileage switching to royal purple gear oil in front and rear diffs. It went up almost 1 mpg, consistently. A true before and after test. Same fuel, tires, pressures, engine oil, driver, route for mileage, weather, gravitational constant, etc...)

 

Pinned ftw

 

Mine looks different than this. But same general idea. I used the 2nd smallest Allen key to fit through the holes.

 

This is what I've always wondered...where does this moisture come from? Is there a breather valve that relieves pressure when it gets hot, pushing vaporized water out, but as it cools down it pulls ambient air (and therefore moisture) back into the transmission?

 

yes. It is a breather/vent similar to the rear diff.

 

My brothers 2500HD rarely gets the ATF over 160. His trans fluid must be half condensation at this point.

 

and, given these variables,

the hotter you run the trans, the more variance from ambient you will have & therefore pull in more moisture when it cools.

I realize this is a bull shit theory, but it should be considered a pre-ponderousment.


that being said - we agree, the moisture thing is a red herring.

kinda like how Toyota WS is better than Valvoline Maxlife.

 

I hear you. For the sake of argument, his was designed to run at 160ºF. Yours was not.

Our Yukon never got past 160ºF, either. It had the heavy duty trailering package (oil and air coolers). It started hesitating toward the end of our ownership.

Counter-ponderance: I think that makes sense, but there is a point at which you're running it hot enough to boil it out.

175ºF is significantly hotter than ambient temp year round no matter where you live. Breather valve gonna breathe. 175ºF is also significantly lower than the boiling point of water. Is it a problem if your transmission never boils it out? But is it even a significant amount of moisture? I suspect as @Silver17 point out, it is not.

 

I guess I’m just wondering what critical difference there is between his transmission and ours that makes ours supposedly love hot ATF so much more? I don’t think there likely is. There is clutches, a torque converter, solenoids etc. in both. I don’t think Toyota is doing anything special with the trans. I think it’s purely an efficiency thing, as hotter fluid is less viscous and less viscous fluid takes less energy to pump.

As far as the moisture goes, the fluid doesn’t have to reach 212 degrees for moisture to evaporate out of it. You’re thinking of boiling a pot of water perhaps, but as we all know moisture evaporates at room temperature let alone the 170-200 degrees that these things will run at with the cooler pinned open. The more heat there is the more quickly it may evaporate, but reaching 212 is definitely not required for that to happen. I’m also wondering where this supposed moisture goes once it “boils out”. Assuming it flashes off to a vapor, it then floats around in the trans until what, the pressure bleeder burps it out? It’s not like there is a water separator in the trans that is dumping condensation out. Just thinking out loud here.

 

Yeah, I'm just thinking out loud here as well. I suspect that in the end we're talking about such a small amount of moisture that it's negligible. I also think 99.99% of Tundras out there, including all the super high-mileage specimens, are not running pinned thermostats. And that's assuming they even have the tow package that includes a thermostat in the first place.

Yes, a drop of water on your countertop will evaporate at room temp. That's a controlled environment with your HVAC acting to dry the air out. Similarly, that water drop will also evaporate outside. Sunlight and wind and a drier moisture content in the air will act upon it as well. Evaporation happens significantly more slowly when there's already a lot of moisture in the air. Like in Tennessee (or Houston @nobodyintexas). There are puddles year-round on some of the trails I run here. They never get direct sunlight, and it's humid enough here that they just don't ever dry up, even when it hasn't rained for a couple weeks.

Does it follow that moisture evaporates out of transmission fluid in the same way? @hagrid mentioned something in another thread that I think is relevant. I said I don't exactly take comfort in new ATF that can handle temps north of 250ºF because it's still stressing the internals of the transmission out. He said the secret with the new ATFs is lower oxygen content, and therefore less harmful oxidation.

Pure speculation here: would moisture in your ATF cause more oxidation over the long term?

Again, just thinking out loud. I'm as careful as anyone to make my truck last as long as I care to use it. I just don't think pinning the t-stat open is necessary or really beneficial. A cooler to prevent temps from running away? Definitely.

 

Water evaporates at every temp above zero

stop worrying about water in trans

at least if your not traversing gullies

 

It’s kind of like how many tundras have achieved high mileage with 0w20, but I still say 5w30 is the better option given the choice. Even @nobodyintexas has oil analysis that agrees with that point for example, yet many say “the engineers” say otherwise so they refuse to run anything but 0w20. I think there is no wrong answer that will subsequently kill your transmission, just do what you think is right for your truck and use case.

My thoughts and experience are when towing with it pinned it will hang out closer to 200 degrees. With it unpinned it was more of a 220 most of the time experience. If the thermostat opens at 195-200 so as to say “im too hot, cool me down” then wouldn’t I be better off towing with it at 200 than 220? It’s as if the thermostat doesn’t allow full flow to the cooler despite it supposedly being “open” at 200. Others have commented having the same experience, including others who were very skeptical but pinned it open anyway and monitored their temps to find they were lower under those conditions.

 

I probably didn't communicate efficiently.

What I should have said is transmissions no longer have a vent in the traditional sense. There is a pressure regulating valve instead. Because of that, there is no longer a free exchange of gasses, hence the transmission interior becomes an oxygen depleted area. The fluid, which is probably the same chemistry going back 20 years apart from the base stock, doesn't oxidize as quickly as in vented transmission.

 

Maybe we need to send transmission fluid to Blackstone as well to further support our speculations.

I don't have any data towing heavy. But this makes me think your t-stat isn't opening all the way on its own. I watch my temps all the time, and once it hits 195-200, it just stays there. The only time it doesn't is if I'm driving somewhat aggressively at elevation on long grades.

I would think that once my t-stat opens, it's a moot point as to whether I had it pinned or it got there on its own.

 

I spoke with IPT and he stated running a cool ATF is ok...

 

I agree, that is a plausible conclusion and I was once of the same opinion. In practice it has proven otherwise though for myself and others. IIRC @snivilous had the same thought going in but decided to give it a try anyway, and he had similar results to my own. If you’re not towing heavy you’re probably not gonna see that 220+ but on the rarest of occasions, even with it unpinned. Towing a 7500lb billboard with a front surface area of 80 square feet up a long grade with an unlocked TC has its way of turning the heat up a notch in the ATF to levels you’ve never seen before.

 

let be written, so let it be done

 

Keeping my thermostat pinned.

Temps on a completely stock, unloaded truck on a 113 degree day:

 

98* ambient. 80mph for 3hrs. Unpinned. Trans set between 197-203*. Good enough for me.

 

Spraynard loves him some Allison transmission service procedures on his pappy's motorhome Le Behemoth.

 

I would love to hear his opinion of optimum trans temps for his ab60.