What's an acceptable max temp for transmission fluid before it's considered to be too hot and about to cause damage?
I had a transmission temp gauge installed in my 1999 Ford Expedition this year; normal operating temp seems to be in the 160-170 range. I have the EOD, 5.4l V8 with 3.55 axle.
Even when plowing (usually not long - 15 to 20 minutes), the temp stays in that range.
However, when I'm done plowing and head out on the road, the temp will usually jump up to the 200-220 range. It will sometimes take awhile (10 minutes or so) so come back down, but it will fluctuate in the process (ie: move down to about 190 then back up to 220).
Last week, I started it after it had sat about five hours, drove for about a mile, shut it off to run an errand, came back and started driving (not plowing). The gauge shot right up to about 220 and stayed there for about 10 minutes. That seemed odd, as the engine, etc. was basically still cold.
I do have an auxilliary transmission cooler (from the factory, as it has the towing package).
The transmission was serviced by a transmission shop about 1,400 miles ago; they were the ones that installed the gauge. They put in synthetic fluid and replaced the filter.
Is this temperature swing normal or does it indicate that something is going to go wrong? Shifts and runs fine; no strange noises.
Thanks.