Hi Guys,

I've been chasing this issue for several weeks, and have done all the searches and internet research that I can. Now I just wanted to ask for some "Second Opinions" before I go any further.

The car is an 89 IROC with the stock dual fan setup, and has functioned perfectly for years. Now, the fans fail to come on at all and do not cycle as they previously did. My chip is programmed to turn the fans on in around 175-ish (and has done so for years). I have replaced the temp sensor in the intake manifold (GM unit) and also the fan switch in the pass head (with a lower temp hypertech unit), but the fans still will not come on (I don't let the car get much hotter than 240-ish by the stock guage, then I turn it off). FYI, both fans DO operate when I short the a/b terminals in the ALDL connection (I'm assuming this means that the relays and such are functioning properly). Is it maybe the ECM not turning the fans on as it should?

As an added confusion factor for me, none of this started until I drained and flushed the coolant in the car. This required me to remove the radiator (and obvioulsy manipulate the fan assembly). I initially thought that I might have broken/pinched a wire on the fan assembly, but like I said, the both fans run via the ALDL connector.

Also, I just turned the A/C on and the fan(s) did not come on.

Any suggestions would be much appreciated.

Thanks - Mike...........

 

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Thanks for the headsup Nina, I'm checking all those connections now. Meanwhile, earlier I let the car "just run to see what would happen." The gage would indicate 240-ish (no fans running) then start to drop dramtically to around 175-ish, then the fans would come on. Based on that (and coupled with the repective locations of the temp gage sending unit and the CTS) I'm pretty sure I've got a sticking thrmostat - and I just finsihed changing it. I'll start it up tomorrow and see what happens.

Thanks - Mike..........

 

Mike, keep us updated. I too am having issues. My primary fan turns on, but the secondary fan does not.I replaced the sensor in the head, the fan motor, etc. - no dice.

 

Probelm solved - it was a sticking thermostat (an easy fix for a change).

I went back with a 180 (with a few holes drilled in it), and the car runs fine and the fans cycle properly as before. Just FYI, my car will overheat with a 160 (or any "high-flow, large orifice thermostat), as the thermostat opens too soon, consequently flowing too much water too fast through my stock radiator, therefore preventing sufficient heat removal (not enough residence time in the radiator), resulting in overheating (esp. with the 383). The secondary fan switch I put in is a Hypertech p/n 4026 (175 - 166 degrees), and it works great. My chip is set at 175, so both primary and secondary fans come on right around the same time just as the thermostat starts to open. It's a perfect balance and always keeps the car cool (165 winter & 185 summer), even in South Georgia with the A/C running.

These dual fan cooling systems use so many different sensing & control locations (temp guage sending unit, CTS, and secondary fan control switch) that you really have to understand the system and think about what's happening to properly diagnose a problem (these many different variables can make it so complicated). The thermostat was the last thing on my mind, so I immediatley jumped to troubleshooting for a "system control" problem. But as I studied the indications that the car gave me, it was seemed that the thermostat was the issue (luckily, as I hate to think what I would have done next....).

Thanks for all your help guys, I appreciate it.

Later - Mike...

 

Hey would you be able to tell me then where my coolant fan switch is? I have to determine if it needs replaced. I Noticed I have a coolant temp sensor on top the engine by the thermostadt. Thank you for your time.

Robert

 

this is for 86-iroc, does your fan come on if you turn your controls to defrost or ac on