what is the 'acceptable' operating range temperature of an automatic transmission and what would be considered the absolute worst operating range.

 

I am not an expert on automatic transmissions, but I do know that too much heat, even for a short while, can damage them. From what I have read 175-200 F degrees is
an acceptable heat range. I would certainly add an external cooling unit to your vehicle and perhaps a temp.gauge if you believe that you will need it. Will you be towing with this vehicle or hauling lots of weight? If so I would absolutely use an external cooler, and change AFT fluid and filter more often. That will add many miles to your automatic transmission, no matter what make or model.

 

I agree with oil's reply. Anything over 200 is too hot. 175 would be the max I would want to see. Gm has a temp to fluid life chart and 200 is on the higher end for shortening the life of the transmission fluid. I run 170 towing with my hd after adding an aftermarket trans cooler. I was running 180-200f after my rebuild and decided to upgrade the cooler.

 

You are correct. My late father's C-20 auto trans burned out at 30,000 miles. Of course, he was hauling heavy loads in it 5 days a week with no external cooler, so it had nothing to do with GM's auto-trans. After that he added the external cooler with a beefed up transmission and it lasted a long time. Me, I prefer manuals in a pickup truck although I am disappointed that my K-1500 with an NV-3500 transmission is only rated for 2500 pounds of towing capacity, I never tow with it. I'd go up to the K-2500 if I did with an stronger NV-4500 transmission.

 

I like my granny gear in a stick but the allison is perfect for towing as far as I'm concerned. Put it in tow mode and it because a beast. Engine breaks itself to almost a stop. First gear gear ratio is perfect for take off with any load. Torque converter begins to lock up in second gear in tow mode to keep heat down while towing heavy. Love it.