I have a lo3 91 rs . My fan will not come on, I have replaced the fan switch on the passenger head between 6 & 8 cylinder. I ran the can and the temp got up yo a little over 220 without the fan coming on. Before I put in the new fan switch I grounded out the wire to the block with the key on & the fan came on. My question is does the fan switch only work as a secondary way of cutting on the switch? Should the ecm cut on the switch at a certain temp? If I turn on my a/c the fan turns on. Could it be the ecm temp sensor in the front of the intake? I have a single electric fan.

 

On my 88 the fan switch and knock sensor are on the other side of engine

 

There are lots of threads on this. I believe the fan comes on when it gets hotter. These cars run hot.

Kevin

 

I finally installed a seperate temp probe, relay, fuse & keeps temp where I want it now

 

I just did the same thing today, Probe fan switch set @185 & 170 thermostat, NO MORE PROBLEM