Re: Cause of rising and falling overheat in 2002 Olds Alero?

That should test at least one fan. Probably two relays for two fans. I was just looking at my cavalier. I don't remember temp going up on idle, but not too high, but does now.

I checked everything on my 2001 . The temp gauge seems ok, and that is what the computer is looking at to turn on cooling fan through a relay. Fuses too.

Greg

There are possible mechanical and electrical problems.

Mechanical... Clogged radiator (replace radiator) Blocked front of radiator (clean) Thermostat (replace)

Electrical... For this you will probably need to consult the factory service manual set of books for this vehicle to see how these systems work - should work. And have the FULL electrical diagrams manual for troubleshooting.

The sensor which activates the electric fan. (there are probably two different sensors, factory manual would say which is for what.) The electric fan. Power and wiring to fan, relay(s), temp sensor(s), fuses.

Electrical A/C... If the problem only happens with the A/C on...

Then is engine computer getting A/C "on" signal? A/C pressure sensor may be used as signal to activate 2nd fan.

Also the engine computer perhaps "should" increase the idle speed a bit when A/C on. Consult factory service manual set of books for this. (Order books from dealer or helminc.com)

that's the coolane temp sensor.. usually located by the water outlet, or on the radiator.

Chas

Start the engine and let it warm up. Turn on the A/C and one fan should start running.

Shut the A/C off and that fan should stop shortly after.

Now with the engine warm the fans should start running when the coolant temp hit's about 210-215 degrees or so. The fans are controlled by the ECM through a pair of relays under the hood. Should also be two fuses on the power side and one for the ground. Fan 1 (left side) takes a 30 amp, fan two (right side) takes a 15 amp. The ground fuse (30 amp) is number 55. There is also a fan mode relay, it controls which fans run based on temperatures and A/C mode.

If the car has a temp gauge that works the coolant temp sensor is OK. If it only has an idiot light the easy solution would be to rent/buy a scan tool that reads live data and watch the coolant temperature. If the sensor is OK you will see it in the data (temp will go up smoothly as the engine warms up)