I have a 1991 V6 automatic Toyota pickup. The transmission has ~230,000 miles, but the engine has been rebuilt and probably has less than 5,000 miles on it. I am having overheating issues in both departments.
Engine overheating: This has started fairly recently. My truck began overheating at idle (usually at longer traffic lights) and would cool down again once I began driving. My coolant was low, I took it to a shop, and they fixed a small leak. Fast forward a few weeks and it happened again, and this time when I turned on my heat full blast to take heat off the engine it blew cool air until I started driving. Took it back, they found no more leaks, and couldn’t duplicate the overheating symptoms. They also said the fan and thermostat seemed to be working fine. It seems to happen sporadically, regardless of coolant levels.
Transmission overheating: Firstly, my truck tends to delay/hard shift when I first start it in the morning. Once the engine warms up it goes away for the most part. I took it on a 100 mile trip camping on a fairly curvy/hilly forest highway and the A/T Oil Temp light came on. This has happened before when I took it on forest roads, even after a recent ATF flush. Needless to say I had to stop a few times to cool it off. It felt like the transmission was working too hard at a flat 60MPH (2,500-2,800RPMs). A couple times the RPMs were pulsing like it was switching gears back and forth. The next day driving in town everything was back to working order.
I’m not sure if these two things are connected… but they never happen at the same time. I’m taking it to a transmission shop but I want to make sure they don’t try to rip me off unless absolutely necessary.