Is it safe to pin open Transmission thermostat?

my '20 did not have a thermostat.

others did.

so there's that.

"running as Toyota designed it" please expound on running a Tundra without secondary, thermostat reliant cooling & how it was designed that way.



yes, they are reliable...most transmissions are.

just keep them cool.

and here we are.

 

Your 2020 doesn't have a thermostat because there is no external ambient transmission cooler.

 

The original question of this thread. Is it safe to pin open transmission thermostat. I have a tacoma tundra and a highlander all pinned open never a issue with any of the transmissions. So yes in my 3 vehicles it is completely safe and also lowers the temps between 10 and 15%.

 

we know this. as stated above

the questions remains.

 

This thread is about as useful as 0w vs 5w.

 

It’s been a while since I’ve towed the camper, coming back up on camping season now of course. As I recall it generally had the temps about 20 degrees cooler under all scenarios as others have mentioned. It will run cooler in S4 then S5, but with it pinned S5 is more manageable as far as temps go for extended highway runs and it keeps it around 200. Before being pinned it would sit at 220 in S5. Basically the temps I saw with it unpinned in S4 are similar to the temps I see with it pinned in S5. I get it that theoretically the temp should be the same once the fluid is at the opening temperature setpoint of the thermostat and it is heat soaked, but clearly in practice it doesn’t work that way based on a half dozen people’s reports of personal experience with it pinned on just this one thread.

I don’t think any temperature between 160-230 is going to be detrimental to the transmission. One thing I’ve consistently heard over the years however is HEAT is what kills transmissions, no question. Heat will also lower the service life of the fluid. It’s a no brainer to me, if I can run the trans 20 degrees cooler and still be well within operating range of the fluid and transmission then why would I not do that?

 

The question has nothing to do if you should be running the transmission without the thermostat working.

It's really simple, the transmission is very reliable and is engineered to work at a specific temperature with the thermostat. Running colder than designed doesn't have any advantages when it comes to reliability. If there is no advantage with pinning the thermostat then why would you do something that could possibly be problematic long term to gain absolutely nothing?

Anyhow I'm done chasing tail.

 

Because it lowers the temperature of the transmission fluid.

 

Logic would say 200 degrees is the ideal max temp for the fluid to hang out at since that is roughly the thermostat setpoint. With it pinned open while towing, mine hovers right around there. That sounds ideal to me. If 200 is ideal and 250 is too hot, why the hell would I want it sitting at 230 when towing if I can prevent it?

 

^ this. It isn’t a one size fits all answer. Climate and use are what dictates what makes the most sense for your application. I normally go unpinned but if I’m towing heavy when it’s hot, I’ll pin it open - I don’t like seeing 220+.

 

Agreed, basically everyone just do what you think is best for your use case and your personal truck. Based on responses to the thread, the original question of “is it safe to do so?” has been answered and I believe it is a yes. Me personally I think I’ll leave mine pinned especially for summer towing, maybe unpin again for winter.

 

When I bypassed the throttle body coolant I ditched the coolant lines to the transmission heater. That was about 2 years ago. Had it pinned for almost a year. No issues. Picked up some elbows to permanently remove the thermostat.

 

What temps do you see for your transmission with the heater bypassed and the thermostat pinned open?

 

It was pretty mild this winter. It gets up to 133deg within 20 min of driving. I only tow about a ton of gravel or cord firewood. I didnt see anything over 170deg. Usually 150-170. Over last summer when I monitored it was always under 190deg. I'm second guessing keeping the trans cooler thermostat as we may get a colder winter coming up.

 

Bumping an older thread - what is everyone using to pin the thermostat open with? Any pics?

 

large Bent paper clip

 

I used a drill bit to pin open my Tundra, and Highlander and a cotter pin for my Tacoma. Both options have worked for years.

 

Thank you!

 

You get those installed yet? Any pics? If memory serves, john at IPT mentions them in one of his videos. Just can't seem to find it and I'm being lazy...

 

I grabbed the part numbers from John's video and talked to him about cooling the transmission.
I removed my warming/cooling puck and thermostat completely in May. Installed the elbows that go straight to the cooler.
I was thinking those without a cooler could plumb the outlet from the radiator to an external cooler and treturn to transmission. You could use a inline barbed thermostat like the 145 deg one mentioned on some Gen 3 threads. A lot cheaper than some other systems out there. Using a 19 row cooler, thermostat and elbows is under $400 for those that don't have a remote cooler. There are a few options to cool the transmission.

 

just another useless update.

It's been consistently Africa hot in Houston.

My pinned trans rarely, if ever, exceeds 180.

I cruise @62mph @ 165-ish.


As stated before - I thought I would settle out around 185.


I wonder if the A/C, being on ALL THE TIME, is helping cool the trans radiator?

 

If anything it would probably make the situation worse, but I’m not sure how yours is set up as far as which heat exchanger is in front. AC condenser or trans cooler? Air passing through the AC condenser is warmer after going through it since that is the heat rejection component of the system. Hot compressor discharge gas entering the condenser is usually over 200 degrees.

 

Do you have an auxiliary cooler for tranny?

 

I installed the Genuine cooling system ... because my '20 lacked the original

 

Is this as easy as buying the fittings, unbolting the puck, connecting the trans lines to the fittings, and looping the coolant lines to themselves?

 

Yes it is.
I did remove the coolant hard lines and just connected them at the heater outlet from the cowl.
In 50 deg temp it takes me about 15-20 minutes to get up to 150 deg atf. The puck does help get up to temperature quicker and does provide some cooling if you got over 190 deg atf from the torque converter.

 

Sweet. I was actually cruising around Improved Racing's site the other day. I wasn't sure they were legit. But 145* thermostat sounds perfect; full open at 163*. Sounds much better for my application than pinning it open (except maybe in the summer time).

Anybody happen to know the pump flow rate for our transmissions? The compact thermostat is rated for up to 5GPM; the full-size version is rated for up to 20 GPM. I seem to recall somebody like @Jowett talking about the pump flow rate but can't remember where/when.

 

No, not I.

 

I just grabbed a pic of the 145 deg one from Amazon. The 165 deg one will get the fluid closer to 180-190 deg for the WS fluid especially with your cold winters. I didnt see too much info on exact pump flow.
Does the Sequoia have the warming puck? I got my thermostat that I'd let go.

 

I might take you up on that thermostat. I honestly haven’t crawled underneath yet to look for the warming puck. I was mulling things over last night and was about to order the elbow fittings when I realized it might have the puck. I was also second guessing the lower t stat temp.