Minimum transmission operating temp?

[ClydesdaleKevin]

Here's an odd question.  We all know that keeping the transmission cool is the best way to make it last...but is there a minimum operating temperature?

I usually run around 120-150 degrees most of the year, even up big hills...hottest she ever gets is 170, and then not for long.

But if its pretty cool outside, I can have transmission temps all the way down to 90 degrees for extended periods of time.  Is that too low, and what is the danger of running at low temps?

Thanks!

Kev

[Froggy1936]

Reccomended operating temperatures (from the fluid manufacturers) Minimum operating temperature is 150o max is 270o fluid is destroyed along with transmission @ 300o if operated for more than a few seconds at that temp or higher . If you have burnt the fluid an immeadiate change of fluid and filter may prolong use of trans If there is a lot of clutch material in the drained fluid or a lot of metal particles overhaul time has been reached !

The minimum temperature is for the fluid to be thinned enough for clutches to stop slipping from maximum lubrication of cold fluid . Frank

[ClydesdaleKevin]

Hmmmmm...so maybe I should cover my auxillary transmission cooler during the colder winter months when we travel?  With a heat shield type blanket material or something?  I haven't noticed any slipping or anything, but I also don't want to damage the transmission.

Kev

[Elandan2]

Hey Kevin, normally you would run the cooler line through the air to air cooler and then through the radiator tank cooler to keep the transmission fluid at a constant temperature.  There are coolers out there that have a valve built in that regulate the flow until the temperature has come up, but maybe you could set yours up to run through the radiator when necessary, using a bypass valve.  Sort of like a setup for the heater.  Just a thought, I really haven't figured out how it could be engineered yet.  Rick

[cncsparky]

Where is your tranny temp sensor located?

[Froggy1936]

When adding an extra transmission fluid cooler The radiator cooler should be left in the curcuit also To eliminate overcooling  For correct transmission temps the sending unit should be in the transmission (wich is what you need to know the temp of) The small difference from 250o (safe) to 270o (disaster) is too close to take readings from the radiator or the cooler exit wich could be @ 200o wile the trans is being smoked ! Frank

[DonD]

On my '86 chassis, the trans cooler is separate and the engine oil cooler is in the rad.

[ClydesdaleKevin]

The way I set up ours, it runs like this:  The transmission line goes into the radiator, and then from the radiator to the first stock cooler with its own fan (part of the stock dual fan setup).  Then the line goes from the stock cooler to the new cooler, also with its own fan which I added.  Then it goes back to the transmission.  The fans are wired to the stock temperature switch, but also to a toggle on the dashboard via a fused relay, so I can operate them manually on steep inclines if I notice the temperatures starting to rise. 

I don't want to isolate the new cooler, because it keeps the transmission at very good temps on the steepest inclines and in hot weather...but if I'm running too cool in the winter I could cover it with a blanket of some sort.  Obviously I'd rather run a little cool than too hot, but don't want to damage anything.

I'm not sure where the temperature gauge switch reads from, since I have yet to follow the wires to the sensor...but its in the stock location, wherever that might be.

Kev

[ClydesdaleKevin]

A couple of pictures are worth a thousand words:





Kev

[Froggy1936]

Hi Kev. Better to cool than to hot . But if its staying to cool you could reroute the flow to go thru the radiator last on its journey . If its a factory trans temp gauge (GM) the sensor is inside the trans in the valve body.  Frank

[cncsparky]

I wasn't aware that GM put factory temp sensors inside the tranny on TH400's?  I know the later model (E) overdrive trannys have them.