Automatic Transmission Cooling.

[Keyair]

Spotted this great link and article over in the Towing section, and thought it was worth reposting here..

Automatic Transmission Cooling | OldIHC

[streamquest]

Thanks Key,

That's a good article to keep on file.

[4RXLA]

Good article. With the exception of my current tow vehicle (V10 SuperDuty) that has a factory transmission cooler the size of the radiator, I have always installed a heavy duty trans cooler and have never had transmission problems. In 1977, my father outfitted his (now mine) Cadillac with a radiator mount cooler as well as a pan cooler to tow the airstream. All these years later the Turbo 400 transmission is still good as new. I had it serviced a coupe of months ago for the first time in 9 years and the mechanic wanted to re-use the fluid because it was so clean. I told him to replace it anyway. I took my V10 to the transmission shop to inquire about an additional cooler and they said these new transmissions were sensitive to running too cold and that the factory cooler was more than adequate. After towing up steep grades for long distances and noticing my trans temp guage never moved, I would agree.

[ROBERT CROSS]

Doug,

Very true...the newer tranny's are very sensitive too cool running problems,
especially up North here.

If you need to install an aux cooler make sure it has a thermostat by-pass feature. B&M.

On GM's.... if you have a trans temp gauge you'll have a very good cooler and should not need the aux....my experience anyway.

Bob

[dznf0g]

Understand that the newer version of trans fluid, at least for Dexron, are not as prone to thickening up in cold temps as the older versions. I believe that is why the new transmissions are equipped with more cooling capacity.
I have noticed that with the six speeds factory filled with Dexron VI, the transmissions run as much as 30 degrees cooler than the four speeds with Dexron V. That 30 degree differential is true whether running solo or towing.

[A W Warn]

Keyair,
Thanks for sharing the article! It gave me some answers I have been wondering about. My silverado's trans temp gets up in the low 230's when going over the mountains. I did not know what the max temp should be. I did not think I was getting close to overheating, but now I know that is not to hot!

[ROBERT CROSS]

The PCM will go into "limp mode" if over 285 for an extended period. (speed and shift restriction).

Our Burb averages 150-210 while towing. 225-235 heavy load/long grades.

Bob

[A W Warn]

Originally Posted by ROBERT CROSS

Our Burb averages 150-210 while towing. 225-235 heavy load/long grades.

Bob

The Silverado is about the same, even when the temps are in the upper 90's.

I have not towed out in the southwest, yet, so I'm wondering how it would be out there. Any others that will share there experiences?

[dznf0g]

What I found on the 4 speeds, across the GM product line was: running solo in the flats of the midwest, the many company trucks I have had, run 80 - 90* over ambient temperature.

The 6 speeds with Dexron VI (I've driven 3 of them thus far) run only 50 - 80* over ambient.

Towing is too variable (weight, headwind vs. tailwind etc) to assign an accurate range, but I have noticed it to be about the same reduction in the temps while towing.

[Cracker]

I just noticed the other night, while driving home to northern Maine from Portland, Maine, no tow, that the transmission temperature gauge for the Allison was just barely off the 100 degree mark at the bottom of the scale. We were doing about 65 mph, with the air temperture at about 19 degrees. I was beginning to wonder if I had a defective gauge since, as I recall, I usually show about 120 to 125 degrees when not towing, even on the coldest winter days??? Have others noted readings (---or "non readings") this low with the Allison?