So, I've got the ScanGaugeII set up to tow this weekend, and I am wondering what temperatures I can expect towing. I average about 150 degrees daily driving. I see some on board here hit 190 when towing. Is this an average? How high is too high (besides looking at the dash gauges)? Thanks.

On Edit: I finally got my search right and I see all the information (kinda confusing sometimes), but this converter lock-up has me really wondering. My dealer tells me to tow with OD on, unless I'm pulling hills, the transmission keeps hunting, or I need to get the load moving. If keeping the T/C locked is the key to lower trans temps, how will I know when the T/C is locked up?

 

Look at your tach. If in 4th(OD gear) with the TC locked, and give it a little gas, you will notice that the RPMs only go up with speed. If in 4th with the TC unlocked, when you give it gas you will notice the RPMs going up with the amount of gas you give it. When you accelerate from a start and you feel the trannie shift, the 5th "shift" is your TC locking up.

 

190* temps while towing are normal. I usually use the rule of thumb is about 80*F over ambient temps when unloaded, and about 100-110* over ambient when towing. This is with the TC locked, if you're running with it unlocked obviously it'll be alot higher. If you're getting over 200* you should start thinking about pulling over and letting it cool. If you get to 230* then you need to get the fluid flushed ASAP as you've passed the critical temp point.

 

Smoke,

With your trailer, you can try to tow it in OD. If it is flat and the trans isn't hunting and your converter stays locked then go for it! I always tow with OD off. Trans temps run at 187 in 100 deg outside temps. I have seen 210 on steep grades. I have figured out how to pull all hills in 3rd gear with the torque converter locked. If I give it just a bit more throttle, I can unlock the converter and climb the hill with ease. In 2nd gear, the converter is unlocked and heat will build. I say try it in OD. If it hunts, then lock it out. If the temps rise, lock it out. The truck pulls great in 3rd. Pay attention to your tach. It will rise about 400 RPM's when the converter unlocks. A downshift will yield about 1000 RPM's

 

Here is a good reference chart to help determine how much life you have left in the fluid based on operating temps.

The effect is also cumulative. Short term exposure to high heat levels (or even prolonged exposure to moderate heat) can break down the oil to the point where even very short episodes of overheating will lead to failure.

http://www.1962to1965mopar.ornocar.o...fluidtemp.html

 

That chart is for non-synthetic fluids. Mercon V is semi-synthetic, and if I owned a vehicle with an automatic transmission and planned to tow with it, I'd replace the fluid with Amsoil full synthetic on general principles.