Now that I've got my new X-monitor toy I'm watching things like tranny temp when I drive... I found this by googling

"Automatic transmission fluid will provide 100,000 miles of service before oxidation occurs under normal operating temperatures of about 170°F. Above normal operating temperatures, the oxidation rate doubles (useful life of fluid is cut in half) with each 20° increase in temperature.

The approximate life expectancy at various temperatures is as follows:

Temperature Life expectancy
175°F 100,000 miles
195°F 50,000 miles
212°F 25,000 miles
235°F 12,000 miles
255°F 6,250 miles
275°F 3,000 miles
295°F 1,500 miles
315°F 750 miles
335°F 325 miles
355°F 160 miles
375°F 80 miles
390°F 40 miles
415°F Less than 30 minutes"


Any comments? I'm wondering because on a short drive, no load, level road, stop/go traffic, 35 degree ambient temp the X-monitor said my tranny temp hit 190 although it seemed to be mostly around 165. I'm wondering if those temp spikes are normal and if so.. are they OK. Or if my x-monitor is going goofy. I'm also wondering what will happen on a long drive, with 5 tons behind me, going up hill at 90 degree ambients...

btw - anyone know when the idiot light would come on?

 

I've read that the idiot light comes on at 275 degrees F.

I have the X and the highest my trans temp has gotten is 145. It has been cold here but it seems that the guage is reading low to me.

 

Temperature can vary by a lot depending where you install the sending unit, in the pan is a good average, in the line out of the tranny is the best because you will see all of the spikes and it is the hottest there. If you put the sensor on the line going into the tranny it is really meaningless, it just came from the group of coolers.

 

The temp sensor is where ever DC put it..., I tapped the stock sensor in the truck. I'm assuming their engineers know where to get a temp that's meaningful. On the drive home today the temp stayed much lower the whole way. 135 to 145.

odd.

 

The stock sensor is in the pan. Tapping into the line out of the transmission as Mcmopar suggests would probably be more revealing, and more responsive, but the industry standard is pan temperature. Mopar and all the other manufacturers, and the aftermarket dealers, all reference the pan temperature. If you want to compare your temperature readings to anything else, you need the pan temperature. I don’t know where davelinde got the numbers in his initial post, but I’ll bet the source was referencing pan temperatures.