Manual Cooling Fan Control - 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 03-22-2008, 08:55 PM   #1
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Default Manual Cooling Fan Control

I want to get some input before I tear into this - I put a 180 thermostat in my 93 SSEi last year and have been able to run 87 octane so far with no problems. The engine temp stays well below the 200 mark when the car is moving (or the A/C is on), until I stop at a light on a hot day. Then the temp creeps up. My goal is to maintain a consistent temp. I watch my gauges all the time.

So, if I can tie into the cooling fan relays and ground the proper lead (86?) to a switch, then I should be able to turn the fans on and off as I choose.

Anyone else done this? Is there and easier way? Am I just goofy for wanting to do this?
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Old 03-22-2008, 09:37 PM   #2
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A good couple dozen of us have done this. I've personally done half a dozen myself for my cars and members.

But we're not goofy enough to try to run 87 octane. You're killing your motor very slowly. If you can't afford premium, don't drive the car. I have a popped piston here to prove what the wrong octane does to L67'*.

Premium Fuel Required. 91 octane minimum.
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Old 03-22-2008, 10:35 PM   #3
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Good point - I do run 91 in it from time to time... But the cheap gene kicks in and I hit the 87.

I figured (ok, rationalized) that the knock sensor would back the timing off if necessary. I really baby the car.

Is my approach to the fan control correct?
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Old 03-22-2008, 11:19 PM   #4
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the knock sensor retards the timing AFTER it detects knock... it is still occuring. it'* only a few bucks more for premium vs. regular on a full tank.
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Old 03-22-2008, 11:36 PM   #5
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Ha! Yes but my rear is still sore from the last time I filled up with plain old 87!

I suppose I will just bite the bullet... But I thought I read on here a year or so ago that if you put the 180 thermostat in and stayed out of the throttle, you could squeak by with 87. Regardless, it is not that much more.
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Old 03-22-2008, 11:43 PM   #6
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The thermostat has no effect on the octane you can run in any way, shape, or form. Your car requires it.

Price a replacement motor and do the math per fillup (run the numbers on 15 gallons of regular vs. premium).

Yes, you can control the fans that way. I prefer now to ground the wire at the PCM so I don't have to route a wire through the firewall. If you override your low-speed relay you'll get an SES light. Just override the high-speed.
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Old 03-23-2008, 12:07 AM   #7
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Ok - thanks for the fan info. I will only do the high speed...

And I understand about the thermostat - but my logic (ahem, rationalization) is that a cooler engine is less likely to knock. That is what I sold my wife on as to the justification of fooling with the thermostat in the first place. Looks like I may need to 'unsell' her.
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Old 03-23-2008, 12:43 AM   #8
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The thermostat does help, but only when there'* forward motion or fans (turn your AC on Auto, and the high speed fans will always be on).

Your car will still get to higher temps. It just takes longer to heatsoak.
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Old 03-26-2008, 08:02 PM   #9
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Willwren - you are right - no real easy place to run the wire through the firewall. You mentioned the wire from the PCM - in my manual it looks like the dark blue wire for the high speed fan relay.

And it looks like a nice spot on the console for the fan switch. One of the blank buttons next to the traction control button. I wonder how hard it is to get that entire switch mount out from the console.

Where did you mount your fan switch?

Thanks -
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Old 03-26-2008, 08:11 PM   #10
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My switches are mounted to my console differently on both cars. I went for the OEM look as best I could.

My 93 currently has the OLD fan override (still active) mounted below the steering column (wired through the firewall to the relay). It has been superceeded by this (all functions direct to the PCM):
http://www.bonnevilleclub.com/forum/...ic.php?t=50871

My 95 is wired to the red switch shown here:

Although this pic is actually my 93. I have the console switches and status LED'* identical in both cars.

Keep in mind the PCM wiring to both of your cars will differ. I'll need to check if the wire you mention is what I used, can't right now (still at work).
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