I have a '87 iroc with a stock 350 tpi 700r4 setup. The primary cooling fan fails to come on when it is suposed to, at about 220*.
When I ground the diagnostic ALDL terminal the fan in question DOES turn on, but not the secondary one, and my computer doesn't throw any trouble codes. As far as I know that is what is suposed to happpen. My first guess was a coolent temp. sensor, which was a pain to get to, and it didn't change anything. My next guess would be the fan relay but I am not sure if this is the right direction. I have searched under this topic and found that some of you guys say there is somthing in between the last two cylinders on the passenger side head that deals with cooling fan operation. Some of the posts said that a few of you have grounded this unit(?) to make your fans come on any time the ignition is on. I can't seem to find what this is on any wirring diagrams for my car and I can't see anything by looking in from up top, although I haven't had a chance to get under the car yet. So, long story short, what is this thing that's on the passenger side cylinder head, does my car have one and could it be the cause of my problem? Any other ideas and/or info on my problem would be great, thanks.

 

It's an auxilliary cooling fan switch, located somewhere between cylinders #6 and #8 on the engine block. Real easy to change from underneath, and you can get one in just about any imaginable temperature setting. I have a Hypertech switch in mine that brings the passenger side cooling fan on at 200*F, off at 180 something. You can get one at Jeg's or Summit, or check at the local auto parts stores since sometimes they will have this switch cheaper (not Hypertech) to come on around 220*F. Stock for the aux switch is like 238*F, I think. Anything 220 and below makes a great improvement over the stock switch .

 

Instead of changing the fan switch, can't you just change the temp setting in the Prom?


Brendan

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1987 IROC-Z L98,SuperRam,EB 6085's,LPE 219/219 Roller, Crane 1.6RR, EB TPI Base, 58mm TB, ADS 24#, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, MSD 6AL, MSD Blaster 3, Aluminum DS, 94 Disk Rear, Adjustable Valve, Precision 3.73 Gears, Sub-Frame Connectors, Hotchkis Lower Control Arms, KYB Shocks/Struts, Suspension Techniques Lowering Springs, Polyurethan Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm,

To see the ROC, Check out the webpage Here

 

so could this switch be my problem?? does it control one fan or both???

 

The passenger side fan will be controlled by the fan switch (passenger side of block), and the AC pressure sensor. The driver side (primary fan) will be controlled by the ECM. If you want to change the temperature at which the primary comes on then you need to change the PROM settings. Like noted before the passenger side setting can be changed to any setting according to the switch rating.
I have a Hypertech set-up in my GTA. The passenger side has a 176/166 switch, the driver side is controlled by a Hayden adjustable switch, and the PROM is the Hypertech Thermo-Master. If you change to lower ratings and lower your coolant temperature you should also do something to your PROM to keep everithing within the operating parameters in the PROM.
Of course it might not get as warm in Michigan to justify the change to a low temp. system. The adjustable fan switch can be set to anything you want according to the season.
Just my .02
Ozman

[This message has been edited by Ozzy88GTA (edited March 13, 2001).]

 

I had the EXACT same problem. it was the fan relay.

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89' Firebird Formula WS6 L98, MSD 6AL MSD Blaster, Hypertech chip, K/N filter cone,flowmaster 80 series, hypertech air foil, koni shocks, edelbrock trailing arms