Auto trans temp upper limit?

[JohnJMonroe]

I am not the type to just throw parts at a vehicle just because somebody says its a good idea. So I'm curious what is considered to be the upper safe temp limit on the 4runner auto transmission. I can monitor using a BT OBDII reader and Torque Pro on my phone. If I see it getting too hot, obviously I'll get an aftermarket cooler and install it.

I live in Tucson, Az, so obviously it gets hot here. I just replaced my raditor with one of the Koyo's from Amazon.com and have the trans cooler hooked up. I won't be towing anything heavy, but do plan on loading all of my camping gear and family up for trips to Flagstaff (high elevation and very steep mountains) on a regular basis.

So my question is what kind of temps do you consider to be too high for the transmission to function properly?

I've had my 4runner (2002 SR5) for about a month now.

 

[Deezil]

from what Ive read operating temps are 175-215 or so, ish.. everyone has a different idea, I want to keep mine under 200 ideally, Id say 225+ is bad

 

[NateMob]

People "throw" money at trans coolers because the stock trans cooler isn't sufficient to keep the trans fluid cool under towing and climbing mountain passes. Its cheap insurance against an expensive repair.

The bottom line for this is really there is no "upper limit", the truth is that heat is the #1 enemy of every Automatic transmission. Once the ATF reaches operating temperature (150*-180*) anything above that is long term going to break down components(fluid,friction bands,etc.)

You can sort of get by with locking the Transmission out of OD when in the mountains but have fun running higher RPMs the entire time.

 

[JohnJMonroe]

I've been logging the trans temp using Torque Pro and a OBDII reader. First of all, it takes about 25 min of driving to fully come up to temp. It hovers around 205 degrees. And it will quickly shoot up to 220 or so if I do anything other than just steady state driving.

Does anybody know where the temp sensor is in the transmission?

 

[poleclimber63]

I agree with Natemob. I tow alot, and routinely climb steep mountain roads. I bypassed the rad cooler and installed a B+M cooler and trans. temp. gauge. I ran this setup for a year before my engine replacement. Towing on steep hills, I hit 200-210 routinely. During a particularly steep climb behind Whistler BC, I hit 220. I was concerned with this, so when I did my replacement, I installed a second cooler with a thermo-bypass. This Summer the hottest I observed was barely 200, but generally, temps hovered 160-180. Ideal operating temp. is 160. On the few cool days we've had recently, and during light driving, its barely hit 120. Too low a temp isnt a great thing either, so I'll probably block out one cooler this Fall. On other threads here, I've seen a graph showing Temp vs fluid life (viscosity breakdown). Basically, fluid life falls rapidly beyond 200 and at 240 its cooked. Once the fluid breaks down, transmission components breakdown. Synthetic fluid has a higher breakdown temp. which is what I'm running.

Check this out:
http://www.toyota-4runner.org/3rd-gen-t4rs/68732-atf-temp-how-hot-too-hot.html

 

[Buckaroo]

General relationship between trans temp and fluid life attached.....

Buckaroo

 

[JohnJMonroe]

Did some research on this tonight and from the link below, the Tru-Cool and B&M trans coolers are all manufactured by the same company. So I'll be getting the largest one I can get with the "low temp bypass" feature.



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