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chevelle3504speed

Cooling fan operation

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I've got a '95 Olds Cutlass Supreme with an L67. I have cooling fans from a 2000 GTP on it; however, I'm a bit baffled about the way they operate. Both fans run on the low-speed setting. On the high speed setting, only the fan on the passenger's side runs. Is this correct? I checked the voltage on the driver's side fan motor, and it drops to 0 when on the high speed setting. It seems like both fans should run on the high speed setting to me (although I do not know the way the system works). I have had cooling problems with this thing since I put it together last August. It stays cool as long as it's not idling still for >20-30 min. I just replaced the original 3.1 radiator with a radiator with 3 additional rows (when counting vertically). The core of my original radiator was 34 rows tall, while the newly installed one was 37. The radiator shop I purchased the radiator from claims that these 3 additional rows provide the same cooling efficiency with the stock 5/8 inch core width as a radiator with the stock number of vertical rows (34) with a 1 inch core width. This new radiator did help the problem, but I would still rather have both fans running on the high speed setting. That would ameliorate it completely I think. Have you guys with stock early 2000s GTPs observed the way the fans work?

 

Thanks,

 

Andy

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the way all(or at least, most, including w-bodies) GM fans worked starting in 1996 was with a 3-relay system, when low speed was desired, both fans kicked on in serial operation, causing them to run at about half of their normal speed. when high speed is desired, 2 additional relays act to split power into a parallel system, allowing the full system voltage to reach the fans.

 

if one of the high-speed relays or associated wiring were to fail(or never be installed correctly), then I can see just one going to high speed.

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I see, thanks for the information. So just to be sure, even though the fan motors are different (the passenger's side motor looks much flatter than the driver's side) both are 2 speed motors, correct? The fan wiring has not been changed and is the stock wiring for a '98 LTZ Lumina. It looks like I have maxi fuses for the fans. Would there be relays in addition to the maxi fuses?

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So just to be sure, even though the fan motors are different (the passenger's side motor looks much flatter than the driver's side) both are 2 speed motors, correct?

Nope. One "speed" motors. The difference is in how they are controlled/connected (as mentioned above). The low speed puts them in series, making them run at a lower speed. High speed gives them both full battery voltage, making them run full blast. Motors themselves only have two wires each. The shape is probably just to accommodate for engine compartment room, but the power ratings are the same, otherwise the series circuit would be lopsided (not the case in stock fans).

Like Robert says, check the two high speed relays. From his diagram, they are #2 and #3. #2 is a 5 pin. Assuming you wired it up the same as stock, then one is on the driver side, the other on the passenger side.

It looks like I have maxi fuses for the fans. Would there be relays in addition to the maxi fuses?

Yes.

Edited by vipmiller803

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I just replaced the original 3.1 radiator with a radiator with 3 additional rows (when counting vertically). The core of my original radiator was 34 rows tall, while the newly installed one was 37. The radiator shop I purchased the radiator from claims that these 3 additional rows provide the same cooling efficiency with the stock 5/8 inch core width as a radiator with the stock number of vertical rows (34) with a 1 inch core width.

Oops, forgot to mention. Although this may be (doubt it), it would probably help most with highway speeds, where airflow is plentiful, especially to the bottom where said added rows probably reside. Fans, however, only have so much cross section to push air through, so something like a 1 inch core would make a difference. Just food for thought.

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Thanks for the information guys and the diagram, RobertISaar. I do not have the number 3 control relay over in junction box #2, which is stock to the car ('95 CS), which is present in the '98 LTZ #2 junction box diagram. My current junction box #1 is out of the 98 LTZ . Would I be correct in assuming that the '95s relied on just one high-speed fan, since they didn't have the #3 control relay? Would anyone be willing to share the '95 cooling fan wiring diagram?

 

Andy

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I see. I'm slow, but I'm getting it here. I found the '95 diagram. Thank you for the offer though. My current plain is re-wire the 98 harness and put each fan on its own circuit as it was in '95. Although I won't have low-speed fans, it seems the easiest way to get both high-speed fans working. If my logic is correct, the dark green wire on the '98 PCM (labeled as low-speed fans control on the '98 diagram) and the dark green wire on the '95 PCM (labeled as cooling fan #1 control, although obviously not pictured here) function the same way, electronically. The low-speed setting is solely a product of serial wiring, not the PCM. The PCM just grounds the circuit, correct?

 

Andy

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The PCM just grounds the circuit, correct?

Grounds the relay(s), yes.

 

So your pcm can request low speed (ground stock relay 1) or high speed (ground all three relays). Are you planning on running both fans on high for the low speed? Or for the high speed? I suppose you could dedicate one to turn on for low speed and both for high. That might be the 95 stock way (sort of a guess). Either way, that would keep you at two relays instead of having to mess with the existing wiring harness too much. You could also just run them both at low if you do not mind the extra noise/voltage dips.

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One more question. Where does the main source of voltage for the #2 fan control relay come from on the '98 diagram? Isn't the 5 BLK 532 a ground for the #1 fan motor? What am I missing here?

For high speed it comes from the relay you do not have. Look just below the #2 relay for WHT504 connecting.

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Hey guys,

 

I got both fans working as they should. I ended up just wiring in the third relay rather than rewiring the fans to work as they would have originally on a '95 model. I did not realize initially that there was a plug right next to the driver's side junction box with the ground, pcm control, and fan motor positive input. Since I am still running the '95 model driver's side junction box, I only have the male end of the plug (because it's included in the powertrain/PCM harness, which worked out fine in the end. I used a fan relay from a '91 Grand Prix, and attached it to the underside of the cruise control bracket. Thanks again for you guys' information and advice.

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Hi My name is Scott. I signed on to this forum to read about this topic. I have a 97 olds cutlass supreme 3.1 My manual says the 2nd fan comes on at 235f (wtf and whats the point lol) Last year I jumped the 2nd relay to the first. both fans worked for about 100 miles. Then I blew the air meter? 10 amp fuse. I replaced the fuse and it blew rite away. I then removed the jumper and everything worked. While both fans ran the car stayed at 190f anywhere on a 90 degree day.The A.C. vent temp also dropped about 8-10 degrees. I could run the a.c on the low speed fan and had 44-5 degree air out of the ducts. Does any one have any thoughts on how to correctly jump the fan 1 and fan 2 relays? and is the 2000 gtp fan motor the biggest one or is it a bigger fan then the 360mm(14.2 inch) olds fans?   thanks- scott

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Flip the electrical center over, cut the blue wire to the secondary relay and put a 1k resistor between it and the pink wire so the pcm thinks it's still there and doesn't throw a code. Then jump from where the blue wire goes to the relay over to the green wire on the primary relay. The secondary relay won't work with a/c but it will work in tandem with that primary.

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