Originally Posted by Bainbridge_Runner

Thank you Grant Baker, Brodie, Vasinvictor and others for the excellent information.

My AT light comes on after about 5 miles up a dirt, mountain road - low speeds and either 2 or 4WD. This happens reliably. I pull over, engine off, wait a few minutes and the light goes off.

Most of the cooling system incl. radiator was replaced when I had the engine rebuilt (blown head gasket) about 22k ago.

The Runner never runs hot, always low to middle on the gauge.

Based on the excellent information here, I'm going to:

1. Clean up the transfer case cooler.
2. Either add something to the tranny fluid and/or upgrade it from whatever is being added by JiffyLube when they change the oil, etc.
3. Use a heat gun on the tranny pan to see what the temp is. I'm heading out on Saturday and will be doing this then.
4. Drain and replace radiator fluids. How frequently should this be done, BTW?
5. If none of these things does the trick, add a tranny cooler. I'm saving that for last because its about 30 degrees in the mountains right now - and if the tranny warms up now, then its going to warm up in the summer when its 85, regardless of whether I have a cooler or not because I only get about 20 degrees of cooling from the cooler (correct?).

Questions:

1. What do I use to measure the tranny fluid temp down the dipstick hole, as mentioned in one of the posts?
2. How come no one mentions replacing the transmission temp sensor?
3. Will the color of the tranny fluid change to yellow when it is toast?

Thank you to everyone who takes the time to make this forum so helpful. The AT light is the only issue I'm having and really want to get this solved. We go out every weekend on family trips and I need the Runner to be very reliable.