Over-cooling an Automatic Transmission?

[sciphi]

Is over-cooling an automatic transmission possible?

The question arises because a newly installed transmission cooler dropped the transmission temperatures to around 160 degrees F once fully warmed-up. This is in a 1999 Buick LeSabre, whose transmissions (the 4T65-E in this car) have a history of cooking themselves to death. Now I'm worried about chilling one to death!

 

[MolaKule]

Is that input or output temp? If the fluid goes through the radiator cooler to warm it up in winter, I don't see a problem.

 

[sciphi]

No clue. I'm guessing output. Wild guess, though.

The fluid is going through the radiator cooler, then through the aux. cooler and back to the transmission.

 

[Kestas]

As I understand it, ideally the fluid should go through the aux. cooler first, then the radiator. This would still cool it, but keep it from getting too cool, especially in the winter.

 

[Eddie]

Need a automotive lubrication engineer to really answer this one I think. I have read many times and in past years have read articles that state some engine & gear oil additives need to be above a certain temperature of achieve optimum performance. Don't really know about AT fluids but, suspect there must be an ideal temperature range for best performance. Maybe someone, working with auto manufactures with real data will share this information. Ed

 

[friendly_jacek]

160 F is almost normal as most trannies run 175 F. Once I had a heavy duty AT cooling in subaru due to boat towing. It resulted in poor MPG on a winter trip north. I think this is the only negative about overcooling. Now, the newer AT coolers are thermostatically controlled to some extend. Nor sure how well it works (it could be just a marketing ploy).

 

[MysticGold04]

My truck has an Aux cooler installed after the radiator, so my tranny gets cooler fluid. They say heat kills trannies, but I do know that if the fluid gets too hot it gets toasted.

Where I live it is usually always 95-100F in the summer and about 25-30F in the Winter. I don't seem to have any problems in the winter except just waiting for the fluid to heat up so shifts smooth out.

 

[sciphi]

Some new data from my particular application is that when the temperatures dive into the mid-60's F from the mid-90's the transmission fluid temperature also takes a dive. This proves the cooler is working just as intended. However, it's TOO cool at 130* F when fully heated up in 60* air temperatures at highway speeds. Symptoms were sligtly higher RPM's as the car vainly tried to warm up the transmission.

I will be re-routing the cooler to go from the transmission to the cooler, through the inline radiator, and back to the transmission to stabilize temperatures at a higher point.

 

[ekpolk]

Have you considered just masking off the trans cooler during those times when you don't need or want the extra cooling effect?

 

[ARB1977]

In the winter months block the aux cooler. My Tacoma has always ran cool and has never had an issue.