Why does my fans kick on after I start my car, after it has set all night? I can start my car in the morning for work and about 30 seconds after the electric fans kick on. Is this right or is something wrong. Is there a temp sensor for the fans and if so where is it?

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91 Formula WS6
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I'm no expert by any means, but I've had the displeasure of working on my fan also. Actually, you're quite lucky that the fan runs all the time instead of not running at all and overheating. There is a fan temp sending unit screwed into the side of the block almost straight above your starter solinoid. What it basically does is ground the circuit when your engine (water) temp reaches 210-220 degrees, and causes your fan to run. Sounds like either your sending unit is constantly grounding the cicuit because it's faulty, or the wire going to the sending unit is grounding somewhere by rubbing on a bracket, block or whatever. One other thing it could be is that your fan relay on the firewall is stuck. If your car only does this when you turn on the A.C. (if you have it), then disregard the above, because when you turn your A.C. on, the fan is then controlled by the ECM module, and I couldn't tell you how to fix that. Good Luck!! Hope this helps!

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Freshly rebuilt 19831/2 or 3/4 Camaro Z28 305 H.O. 3:73 Gears, BW T-5, Duel Snorkle, Rhino Clutch, 2040 Compu-cam, LS1 valve springs, porting, PST front end kit, K&N Filter and runs great but ain't streetable yet!!....Future Mods: Not yet decided if I'll keep it!

 

Ron,

I know it's pretty basic, but is the A/C compressor running when the engine is started? Either A/C, Bi-Level, or Defrost will run the compressor, and therefore, the fan.

If that's not a problem, the secondary fan is controlled by the CTS in the right side head. If the wiring is shorted to ground or the sensor is failing, the fans could run. The primary CTS for the ECM could also be failing or have grounded wiring, causing the primary fan to run constantly (key on).

Later,
Vader

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"Some Body...Someone"

 

Ron,

I have a '91 (but a Camaro), so it should be essentially the same.

Are both fans coming on (at the same time)?

If so, the only thing that would turn on both fans at the same time would be the AC (or defroster if outside temperature/humidity - can't remember which - is high), so the AC (or defroster) would have to be on. Turn your climate control to off or vent.

When the head pressure of the AC reaches 232 PSI, the ECM will turn on the left fan. The right fan will also turn on by a mechanical switch on the AC high side when it detects a pressure of at least 232 PSI. (FYI, the right fan is only turned on by one of two mechanical switches - one's a thermal switch above the starter, the other is the one mentioned above.)

FYI, when you turn your AC off, the ECM will keep the left fan on for about a minute afterwards. The right fan should go off immediately (unless coolant temperature is high).

[This message has been edited by Stuart Moss (edited July 28, 2000).]

 

Thanks everyone. I thought that the switch/sensor might be in the block on the pass side but wasn't sure. I was thinking maybe because I had headers and they were somehow heating up the sensor faster than normal. I'll check it out in hte morning or late this evening.

Thanks again.

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91 Formula WS6
Home Made Ram Air,K&N Air Filter,Air Foil,
Ported Plenum,Underdrive Crank Pulley, Crane AFPR, Edelbrock High Flow TPI Runers, Holley 19lb Fuel Injectors, SLP Headers, SLP Y Pipe & Complete SLP 3" Exhaust and Muffler, High Flow Cat, Mobil 1 Oil, Hotchkis STB, Spohn LCA's and Panhard Bar and other polyurethane goodies.

Http://www.geocities.com/91formula

Add your 91 F-Body to my 91 F-body's Links page, or be added to my F-Body Links Page.