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Thread: Running hot, Cooling fans on late?

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    Senior Member Prospeeder's Avatar
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    Default Running hot, Cooling fans on late?

    Well, all of a sudden, my 6000 has been overheating going up hills, it gets almost to the red climing a hill! I get out when the gauge is near pegged, and the engine doesnt SEEM that hot, but the cooling fans finally kick on and it cools right back down. I let the car sit at an idle, it will slowly climb, and the damn fans wont come on to cool it back down till nearly 3/4 of the gauge. What the hell!? Today, i put a new Waterpump, Thermostat, and coolant temp sensor just too see, and I have the same issue. i havent taken up a hill yet to see if its still overheating up hills. Fans come on late, fan works good, relay is obviously working, what gives??? Could i really possibly have a bad ECU or somthing? The radiator is nearly new, and looks fantastic inside. I did headgaskets 30k ago also, so that shouldnt be an issue. Any ideas, cause im about out of them
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    Senior Member CamoDeafie's Avatar
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    sounds dumb, but did you check if your water coolant level is going down or staying at the same level? (IE< you;'re losing coolant somewhere) Im also thinking, when was the last time you did the Intake Manifold gaskets?

    otherwise...ECU/ECM....*shrugs*
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    Senior Member Prospeeder's Avatar
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    Well I just did headgaskets, so the LIM was definatly done, remeber too these engines didnt have that problem. I dont loose coolant....
    Anyone know if the 2.8/3.1 computer from a W-Body car work just fine, if i just swapped the PROM. Its from my TGP, well its from a 2.8 Cutlass Supreme but worked fine in my TGP
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    Senior Member SilentWing's Avatar
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    I know for a fact that the W-body ECU can be finicky with the cooling fans, because for some reason Luke's refuses to turn both fans on when the A/C comes on. I don't remember if it's the primary or secondary that comes on as soon as you turn it on, I think it's the secondary though. Also, the W-body's temperature will climb to about 235-240 before it'll turn the fans on. I'm not sure why it's so high on those cars but that's what Luke's will do. He ended up wiring both fans together so that when the radiator fan comes on, both fans come on. I haven't been up-close to too many 6000's, but I know on Luke's supreme the grill is small so it restricts the airflow more, I think your picture is decieving because I can't see the 6000's having that same problem. Did you by chance have the A/C on when it happened?

    I just re-read, maybe it was fine in your TGP because the TGP and Supreme's were basically the same? Which would make sense since my fans come on at 220 and Luke's at 235-240 and 220 is about halfway up my gauge on the dash.

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    Senior Member dcjredline's Avatar
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    Check the ECU numbers, I would think that they are the same and a simple PROM swap would do it but check the stickers if they are still there if not do a cross reference on Autozone or Advance websites.
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    Senior Member LordDurock's Avatar
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    you might want to get a harbor freight lazer thermometer and check the temp to verify the temps next time it it happens

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    Senior Member Prospeeder's Avatar
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    true, it could be the gauge is reading high, I find turning on the A/C if its getting hot at idle quickly cools it back off. Its gotta be some fan issue..
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    Senior Member SilentWing's Avatar
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    If it cools right off when you turn the A/C on maybe it is the difference in running temperatures between the ECUs?

    Oh nevermind I misread what you said about what's currently in your car. I'm not sure if it would fit in the ECU. I'd go with LordDurock suggested and get a laser thermometer then, if for nothing else than peace of mind knowing that it's not actually overheating. If you do get one from HF though make sure it's the CENTECH one and not just the cheapy one (the cheap little one is a total POS)

    Do you by chance have the fan fuse boxes under the hood? I don't think our cars have them... I know the w-bodies liked to crap out the fuse box under the hood.
    Last edited by SilentWing; 06-12-2010 at 12:31 AM.

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    The gauges are known to read high on these cars. There's even something about it in the factory service manual. The easy way to fix it is to wire in a resistor to the signal wire, but it's trial and error and you need a scanner so you can compare readings between the gauge and the CTS.
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    Senior Member Prospeeder's Avatar
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    well, I got a GOOD laser point thermometer. Gauge says 210, Right at therm housing is 210, Gauge is 3/4, Therm says 240 and then the fan kicked on, cooled it right down to 210. Is 240 degrees when everyone elses fans come on? is that what it suppose to be? Im going up the waterville hill tomarrow so well see if it gets hot up the hills. It will not heat up at idle with the a/c on, but I thought the fan came on as soon as the a/c switch was turned on, mine waits like 30 seconds to a minute before coming on with the a/c on. And somthin else, with the hood open the car at idle wont heat up and the fans will never have to come on. lol

    There arnt any un-used threaded plugs on the 3.1s cooling system i could add a lower temp coolant temp switch to control the fan is there?
    Last edited by Prospeeder; 06-12-2010 at 09:46 PM.
    "Pontiac, Of Course"
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    Senior Member SilentWing's Avatar
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    Not sure about the plugs but I can answer a couple of your questions. Mine's a 3100 so I don't know if that makes a difference, but mine comes on right after the aftermarket gauge hits the 220 mark and when the stock gauge gets about halfway up, maybe a hair over. Second, it always takes about 30 seconds or so for the fans to come on after you turn the A/C on, I'm not sure of the reason for this but that's how it goes. I'm really not sure why your fans would be comming on at 240, the reason I origonally posted about the supreme's was because I thought you had already put the ECU from your TGP into your 6000 which might have explained it since the supreme's fans come on right around 240. The only other thing I would figure would be the intke and/or head gaskets going out again, but seeing as though you replaced them so recently and it's not actually overheating I doubt that.

    The only issue you seem to have is the fans comming on 'late'. And with that being said I don't have any experience with 6000's and I talked to Luke and he hasn't really worked on any either other than oil changes.

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    I still think the gauge may be off, those thermometers are not always the most accurate even if they are good ones. Reading the temp through the ECM is the only good way to compare.

    It doesn't sound too far off. The fan is programmed to come on at something weird like 228 or 232. The hotter it gets, the more the gauge can be off. It can read 240 but actually be 230, but then read 260 at an actual 240.
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    Member ricapper's Avatar
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    what if you rewire fans right to battery with a toggle switch inside so you can turn them on when you want them,instead of waiting for it to come on

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    Senior Member SilentWing's Avatar
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    That's a good idea too, as long as you also allow the ECU to be able to turn them on (luke did this with his old van). You don't want to have the toggle switch be the only way they get activated just because you're not always going to be paying attention. But in your case for uphill driving and such it might be a good idea to do that, also as a failsafe

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    Senior Member Century7667's Avatar
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    I'm late to the thread, but I've observed the same thing Prospeeder has experienced climbing up the parking garage.* The fans might seem confusing, but I plugged the laptop into my Century ('95 3100) and this is what I observed:

    1) The ECU calls for the fans at about 220.
    2) Once you get decent road speed, the ECU will kill the fans.
    3) The ECU may call a fan when the A/C is turned on depending on high side pressure. I'm guessing this is for A/C performance.

    Generally the fans will come on sooner with the A/C engaged. I guess the thing was interesting was that the fans turn off when the car gets up to speed.

    So, back to my parking garage. I watch the needle climb and climb as I climb and climb level by level. Since it's at then end of a 30 minute commute, I presume the A/C is happy since the cabin is nice and chilly. So, the ECU won't call on the fans. Since I'm inside a parking garage at slow speeds with no wind, the engine will just start to heat until the magic 220 is reached, and then the the ECU finally calls on the fans. I don't like watching the needle climb, but apparently it's normal operation.

    In summation, the ECU will call the fans for one of two reasons: 1) The engine is getting too warm, or 2) The A/C needs the air flow over the condenser while the car isn't moving very fast.

    Ken T.
    Last edited by Century7667; 06-22-2010 at 05:22 PM.

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