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Thread: Please help. Serious issue with e46 m3 coolant temp gauge?

  1. #1
    Join Date
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    1999 bmw m3 coupe

    Please help. Serious issue with e46 m3 coolant temp gauge?

    So I was driving my 2002 e46 m3 home tonight and something strange happened. When I got home, I noticed the coolant gauge was in the red zone. I immediately shut the car off and checked both fans and they were intact and spinning. I also checked the bottom of the car and the reservoir and I hadn't lost any coolant.

    I got in the car and restarted it and turned on the heater all the way. The coolant temp rapidly started dropping, the gauge dropped way past operating temperature (to the tip of the blue) and the auxiliary fan started spinning extremely fast. (Doesn't make sense, since the engine (according to the coolant temp gauge) was running cold so I can't understand why the fan would start spinning faster when I turned the heater on.

    When I turned the fan off the coolant temp rapidly started rising again.

    The second I turn the heater back on the temp drops past operating temperature until it's cold but the second I turn the heater off it off it climbs to the red.

    If the thermostat was stuck closed and not allowing water in, turning on the heater wouldn't make the needle drop below operating temp. The car would still overheat regardless if the heater was running. Correct?

    I scanned the car with my peak tool and there was no new codes.

    What could this be? Did my car actually over heat or is the gauge malfunctioning? I checked my oil and there was no coolant in it. I will do a compression test ASAP. I'm really worried I damaged the head gasket but I don't know if the car actually over heated. Please help me guys.

  2. #2
    Join Date
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    '04 M3/MT Coupe,'04 X3
    If the AC is on, the aux fan will kick on. If you run the heater, then the cabin air fan will pull air through the heater core and help cool the engine a bit, although that's not going to make up for a cooling system problem.

    I'd guess that your fan clutch is shot. Fan is spinning, but not with any real power. They're not hard to change, just don't forget that it's a LH thread.

    Or I'm completely wrong...who knows.
    -Aaron
    2004 M3 - Coupe, 6spd, Silver Grey on Black
    | RAC RG63, PSS, ZCP Brakes, aFe, SS (V1, Res. X-pipe, Street Muffler), Epic Alpha-N, 319whp |
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    2004 M3 SMG - Silver Grey on Black, Convertible - RIP
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  3. #3
    dworthy's Avatar
    dworthy is offline Wagon meister :) BMW Tech Expert
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    Also sounds like a stuck open thermostat to me. If the car is over 10 years of age and has traveled 75k or more, it is time for a cooling system overhaul anyway.
    Darin
    Current:
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  4. #4
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    Jacobm3, what was the culprit, please? Did you get this resolved? I am having a similar issue.

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