My primary cooling fan will not operate. I have the secondary cooling fan rigged to a switch. I have a 180 degree thermostat installed. The cooling system builds pressure normaly. The radiator was new about 300 miles ago. My 1990 iroc will consistently continue to heat to 260 degrees and the primary fan never comes on. If I disconnect the coolant switch on the manifold the fan comes on. I figured it was a bad switch right? Nope. I replaced the switch twice with two different brands. It will not come on. Has to be an ECM problem now right? Any other ideas? I even changed the engine temp switch in case it was just an indication issue. I'm out of good ideas.

 

The primary fans runs off commands from the ECM. the secondary fan runs off the Fan switch and both fans should run with the AC turned on. Since your secondary fan is rigged to a manual switch, does either fan come on when you turn the AC on?

 

Not sure what you mean by "primary fan"

https://www.thirdgen.org/forums/cool...ans-arent.html

https://www.thirdgen.org/overheating

Read these, carefully, so you have accurate troubleshooting material. Obviously the fan not coming on at all is a symptom. However, which side? When does it overheat? At what speed/conditions? How long has it been doing this? Are you sure your gauge is accurate? (IE you have checked it with a laser thermometer at the autoparts store) Need a little more history & info to help.

 

Good info Keoman.

 

I have the secondary (passenger) fan rigged to a switch because the AC had been inop for a while and I didnt want it to effect cooling. So neither fan is controlled by the AC pressure switch anymore.