My car (1998 Chevy Lumina) has 208K miles on it, and has been running hotter lately. I asked my mechanic to check the thermostat. He informed me that the thermostat checked out fine, but the transmission came up with some codes indicating it is beginning to fail-that the extra heat is being generated by the transmission having to work harder.

Is this true, and if it is-should I A) get a new transmission-even tho the trans is showing no signs of trouble B) get all the trans fluid changed c) get only the fluid in the pan changed along with the filter?


To be honest, I’d be thinking that the reverse is true; that extra heat is being generated somewhere else, and that’s what is slowly killing the transmission. There is no greater threat to an auto trans than heat.

If the thermostat is okay, you might consider the water pump, a blockage in the radiator/hoses, or (worst case scenario) head gasket.

I had a 97 Lumina and it is normal for the gauge in that car to rise and fall quite a bit, especially in the summer in stop and start traffic. If your transmission is performing fine I wouldn’t listen to that mechanic, in fact I’d never go back to him for telling me a lie just to try selling me a new transmission. Of course change the fluid as you normally would. As long as your temp gauge fluctuates within a consistent range I wouldn’t worry about it at all. Just make sure your coolant level is where it should be, remember Dexcool only.

Yes it is possible for the transmission to overheat the cooling system. The outlet oil from the torque converter is cooled by the heat exchanger in the radiator tank. If there is any slipping in one of the transmission clutches that heat will have to be dissipated by the radiator. It could be the torque converter clutch or one of the drive or reaction clutches. You might not be able to notice the slippage but the transmission computer will keep track of it and set a code. If it gets bad enough the transmission check light or OD flashing light will be set and the transmission will go into limp home mode.