98 Lumina Funky Fan Problem

Hi guys, I have a fan problem on my 98 3.1 that I cant figure out. The fans do not turn on correctly unless the AC is on. From browsing I can answer some of the usualy suspects that others have covered

1. The fans both turn on when the ac is on, not just one of them.
2. The fans do not run solid when the AC is no, they seem to cycle with the temp of the engine.
3. The fans do not turn on if the AC is off, causing overheating if the car is not moving.
4. The car does not overheat if I am moving, in cools just fine (I assume its just that the engine does not run to hot for moving airflow to keep up with.
5. I replaced the radiator myself a year back.
6. The dash guage temp display works (as far as I can tell the engine only has one temp sender unit which would tell me that its working)


I have found that if I am sitting idle (drive through or something) I will turn on the compressor (AC, or defrost) to force the fans on and prevent overheating. Once I am moving again the engine runs at normal temp.

I even drove it through southern navada this summer mid day in 100+ temp and it cooled fine (even with the ac off)...Does maybe speed have something to do with the fan control, maybe they are switching on when I am moving (no way for me to know this..at least not eaisly)


Thoughts?

The factory setting is 230 degrees to kick the fans on, unless the AC is on. I agree that it's too high, but unless you're creeping above 230 and the fans still remain off, its normal.

If the fans dont turn on it overheats to the point of boiling past the 15psi cap into the overflow tank. I would think that is to hot.

I would agree. The same sensor that the ECM uses to detect engine temp turns the fans on. You can try replacing the coolant temp sensor, but I believe if it were bad, it would trip a CEL (check engine light). The other thing to try is the primary cooling fan relay in the underhood relay center. Again, since they come on when you turn the air on, I believe that rules out the relays. Consult a wiring diagram for your vehicle to see if the fans get their signal through the ECM, or if they have a separate signal wire from the CTS (coolant temp sensor), as it could be a broken wire (either from the ECM or CTS) to the fan relay.

make sure your coolant is properly mixed, too much h20 will cause overheating. You need 50%water, 50%antifreeze, no matter what part of the country you live in~!

I checked out my relays ,can start fans manualy but will not start when the ac is turned on.