1988 Mitsubishi Overdrive Problem

I have an 88 Mitsubishi Montero with 172,000 miles with a 2.6 4 cylinder and 4WD. It doesn’t shift into overdrive until it is good and warm. Once it warms up, it shifts fine. The problem I have is when I go down a long downhill grade, it kicks out of overdrive. I’ll pull over and sit for a couple of minutes and then it shifts fine again until I hit another long down hill stretch. It appears to be related to temperature. If the temp. gauge drops to a certain point, it kicks out/won’t shift into overdrive.
Is there a sensor on the transmission or radiator that will fix this?

Could be the temp sensor. Is your water temp steady or it does fluctuate? Also make sure your ATF is at the correct level. SomeMitsu transmissions have the computer set that it prevents “free falling”, so when you let go of the gas on the downhill trip it automatically downshifts.

Fluid level is good. The only info I have on the temp switch is on the wiring diagram which looks like it only gives a light. There is an automatic trans. control unit which is tied in to the overdrive relay and the overdrive solonoid valve. It doesn’t show location though.
The free falling you talk about, should the tranny shift back into overdrive on it’s own when you give it gas? This one I have to stop and st before it shifts properly again.

If you haven’t changed your thermostat in a while, you might try that. If that doesn’t solve the problem you could check the calibration of the Coolant Temperature Sensor. If you are of the change parts philosophy, just go ahead and replace the CTS.

Hope this helps.

I’ll give it a try. Thanks!!

Well the Thermostat worked!! Heck of a lot cheaper than AAMCO! Thanks for the help!