Hi all! I have searched and read these forums, and got alot of good info. but I am still stumped with this problem and would like to get any opinions that i can just in case i overlooked somthing simple.
My ride overheats unless i manually switch on my fan. I have changed the fan switch to a stock unit and also the hypertech unit. I just dont get it! If I let my car warm up by itself the fan switch just does not turn the fans on. but I do know that the wire to the fan switch is good because if i ground it out the fan turns on. I have a 160* thermostat in at the moment, and i have previously used a 180*. if I manually turn on the fan when needed the car will stay in the 175-185* range just like it should. if I just drive the car without manually switching the fan on, the temp gauge will get soooo close to the red zone before the fan switch kicks the fan on.then it will cool it down to about 220* then climb right to the red zone again and again. I just cant figure it out. I have tried infinate combos of thermos and fan switch temps, but just cant get the thing to run cool without me manually turning on the fan myself. I even tried one of the hayden adjustable fan switches, but i just couldnt get that thing to work right.

I have a 91 lo3 305 tbi auto. I checked water pump flow and radiator ETC. all the simple

things.

I would be greatfull for any ideas or insight.

 

You should hook up a scanner to see what temp the engine is running at. My car did the same thing. Primary fan wouldnt kick on till the gauge was almost in the red. I have a scanner and it shows that my engine is running at normal operating temps and the gauge is reading way high. I have traced it to a voltage problem going to my gauges.

 

I will use winaldl later today and see what it says. If the gauges are reading correct, do you have any other ideas as to what might be causing this? This is driving me crazy.

 

if your using the stock fan switch, it has a temp rating of 235 so it doesn't kick on till 235. my 90 iroc the primary fan that is controlled by the ecm comes on right about the same time. i tested this theory by unplugging the primary fan and just letting the secondary fan kick in. if the primary doesn't come on and the temp keeps rising, the cool fan switch will kick in to cool the engine. i'm not sure what the hypertech switch turns on at.

 

I was thinking that the fans on later third gen cars were controlled by the ecm as well as the switch. That would explain why the fans come on at 220 even after you changed the switch. I think the change has to be made at the ecm and the switch on your car. On my car which has a single fan it is controlled only by the switch.

 

On the later cars such as much, my driver side fan is controlled by the ecm and the pass. side is controlled by the switch. have you tired changing your coolant temp sensor on the manifold. it is what sends the signal to your ecm to tell the fan to turn on. its controlled by a resistor in the sensor. when temp goes up, the resistance in the switch changes and sends the signal to the ecm to tell the fan relay to close and send power to the fan.

 

Mine is a 91 rs 305 tbi with the 1228746 ecm. I was under the impression that these were only controlled by the fan switch. Am I wrong?????
I did a scan with winaldl and it seems that the gauge is reading correctly. I just dont get what the !@#$ is going on.
Could it be that the 160 thermo is cycling the water through the motor too soon for the fan switch to actually reach its "on" temp????
I have run out of ideas and I am working on theory alone! I wish I had time to go through everything step by step and find the problem through process of elimination, but I dont. I would be greatfull for any ideas you guys might have to point me in the right direction!

 

Could the relay for the fan be dead? The fan still turns on when i switch to max A/C though. I cant figure this out!!!!!!!!

 

I had the same issues in my cars. Stock switches wouldn't work, expensive ones wouldn't work - I finally got fed up and installed a completely separate fan controller, and it's made me a very happy camper .

I got a Flex-a-lite 31149 controller from Summit, and haven't had any issues at all ever since - easy to install and wire up, and has options for in-cabin wiring for always on/off switches, and completely adjustable settings.