coolant fan - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 07-14-2002, 11:13 AM   #1
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i just perchase a 95 ssei, i notice that both of my fan go on at the same time at around 220.i am thinking this is a little too hot and that if one on the fans should go on first.is there a relay that needs to be change or can i hook it up so that one of the fan can go on as soon as i start the car? thanks
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Old 07-26-2002, 09:45 AM   #2
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Both fans will come on if the AC is on too! You could try wiring in a toggle switch to turn a fan though!
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Old 07-26-2002, 10:35 AM   #3
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I am going to try to wire in a relay so that when the ing. is on so will both fans. I was going to just hook up a switch but them it will create other problem(staying on or not turnning it off). will let you guys know how it comes out.
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Old 07-26-2002, 04:13 PM   #4
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I've been wondering this about my '95 SSE too. Maybe if we all look into this we can come up with something.. I'll look in the factory service manual tonight, but there has to be a way to provide +12v power somewhere and make the fans come on just as the PCM would. I know the grand prix store offers a kit:

http://www.grandprixstore.com/Mercha...egory_Code=004

but damn! $90 What the heck are all those relays for too?? Maybe I'm wrong here, but I would think all one would need to do is find the wires heading to the fan and put a switch from an ignition source on them. That way they would only run when the car is on which would prevent you from forgetting about them and leaving them on. There may however be a problem with this, since you not only would be feeding +12v into the wire going to the fans, but that same wire going back inot the PCM (might be bad). Teuobk, anyone else?? Any suggestions? I'd really like to do this, especially cheaper than frekin $90!!
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Old 07-27-2002, 04:22 AM   #5
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I could build a custom temperature-sensitive circuit, like something with a thermistor, transistor, relay, and op-amp. It wouldn't cost more than $5 and would be trivial to build.

The relays are there to handle the high current that the fans require. The lines from the PCM go to relays which in turn power the fans. If you splice in another relay in parallel with the current relay (on the high current side), you wouldn't have any problems with sending current back to the PCM.
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Old 07-29-2002, 12:02 PM   #6
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How did we ever make out with this?? I'm still very interested in doing this, since especially when sitting in traffic or in line at the track, even with the 180 degree thermo, the car still creeps way up there on the temp gauge. It almost has to get to the frekin 240 mark before the fans come on, and even then they will run for a few minutes and shut off although the motor is still hot!! Once they come on, or once the car is moving again, the temps drop right down immediately, so I am determined to find a way to put these things on a switch / relay to keep them on.. I havent looked into it with the factory service manual yet (to busy wiring in the new audio system), but tonight I want to look up and see if maybe we can get something going on this mod.

There must be a wire coming out of the PCM somewhere we could easily tap into, inside the cab under the passenger side of the dash, without having to worry about running wires through the firewall, etc.. instead of if we tapped into it out by the fans themselves. One thing I never did understand, what what do the ceramic ballast resistors actually mounted on the fans themselves do ? I've sold them before at advance, and I know the fans wont run without them, but what do they do ?? can +12v power be supplied directly to these resistors, with a switch, without a relay?
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Old 07-29-2002, 07:41 PM   #7
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I'll take a look at the manual and see if I can come up with something.

Ballast resistors (depending on who you ask) are present either to a) filter line noise [I doubt it] b) limit current flow [probably] c) regulate voltage in proportion to temperature [seems reasonable]. I'm not entirely sure.
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Old 07-29-2002, 09:56 PM   #8
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I took a look at the service manual this evening. The good news is that it would be simple to wire in a switch without additional relays. The bad news is that it must be done in the engine bay - none of the required wires appear to run to the soft side of the firewall.

To enable the fans, one needs only to ground one or two wires coming off of the PCM. Doing so should not affect PCM operation. Why one OR two? Ground one, get low-speed fan operation. Ground two, get high-speed fan operation.
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Old 07-30-2002, 12:24 AM   #9
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Many Camaro/Firebird drivers instal maual fan switches. I saw a friend of mine do it and it is not that difficult really.

Took hours to convince him not to run the wires for the switch through the driver side door and into the hood though. He just did not seem to understand that doing that would rub through the insulation eventually and cause a short.
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Old 07-30-2002, 08:27 AM   #10
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Once again, I didnt have a chance to look at my book last night :( By the sounds of it though, teuobk might have found the solution however! Now, when you say ground those 2 wires coming off the pcm, your still talking in the engine bay right? Where are the wires, down by the fans, or up in the relay center? What is the difference between high and low? I've never really noticed exactly how they worked, but is low one fan coming on, and high both? or do they actually spin at a lower RPM on low, and speed up during high?

I'm sure I can find in my book which wires your talking about, as far as color, etc..
One other Question.. If we were to wire a switch into this ground, how exactly does the relay work? When the wire we are switching is grounded, the fans are off, and when the ground is broke, they come on? Reason I'm asking is, if I'm going to wire up a switch, it probably wouldnt be a bad idea to go through one of those orange or yellow simple 2 connection indicator lights you can buy at the auto parts store to show that they are on. I'm wondering if there is any current in the ground wire to light something like that, and when it would actually light (when the fans are on, or backwards when thay are off.)

Thanks!
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