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Overheating at idle

Discussion in 'E34 (1989-1995)' started by billygoat777, Jan 25, 2009.

    billygoat777 guest

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    Hey guys recently my 1990 535i has been overheating at idle after driving for a while, but when I start driving again the temp goes back down to half. I have been told this is the fan clutch, and I know that part is known to go bad on e34's but I was wondering if anyone here had any other ideas?

    Also how do you test the fan cluthch, newspaper test?
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    MGarrison

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    Moosehead can clarify this, but I think the test for the fan clutch is fairly simple. Spin the fan clutch by hand when the engine is cold (and turned off!), to get a feel for what resistance it offers by touch. With the engine warm, do the same thing. If the fan clutch spins freely when the engine's hot, then you need a new fan clutch.

    I have trouble judging the 'tweeners' - how can you tell if it's bad when you have some resistance when it's hot? Paul? How much resistance is indicative of a fan clutch being ok?

    billygoat777 guest

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    Thanks man, I just did the newspaper test and the fan stopped. I'm replacing it in autoshop in a few min.
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    mooseheadm5

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    I was out of town, but glad you chose wisely. This is all classic bad fan clutch. Another dead giveaway is that when you cut the motor off, the fan keeps going pretty fast.

    billygoat777 guest

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    Well guys, before we replaced it we tested the old fan clutch again, it is fully functioning, the newspaper test i inaccurate as I had heard, it was just air in the system aparrently because we put a little coolant in since it was a little low and the problem went away. Luckily I didn't do it at home, my teacher saved me $188


    I kinda feel stupid because when it first happened I looked for spewing coolant on the ground but was so dumb I didn't check the resevoir
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    mooseheadm5

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    I am guessing by your description the "newspaper test" is to try to stop the spinning fan blade with a newspaper. If it was hot and you easily stopped the fan clutch, then it is not working properly. Of course, there are different levels of "bad" and yours may just be marginal. That is one problem trying to fix cars over the internet: it is really hard to tell what has been checked prior to the question being posted. Glad you got it fixed, but I still suspect the fan clutch.

    billygoat777 guest

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    Yes that is the newspaper test, but I actually used a rolled up magazine tht was pretty thick, but in autoshop we blocked the front of the radiator with cardboard to get the temp up and the fan started spinning faster when it got hot so I don't think it was the fan clutch... I may be losing coolant though, my light came on but its dark out so I couldn't tell if it was just a faulty sensor which I know happens on these cars, but I'll check it tomorrow. The oil appeared to look normal too so I don't think thats where it's going, and there is no dripping either.
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    mooseheadm5

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    There may be no dripping that you can see. It may only be coming out when the car is running at temp and speed. This can be weeping that gets vaporized by the exhaust heat (common with external head gasket leaks) or it could just be venting past a faulty cap (the very cheapest thing to replace and see what happenss.) Do you smell coolant? Also, just because you topped it off does not mean you got all the air out the first time, so top it up once it is cool again and see if that helps (they burp sometimes and it can seem as though they lost coolant.)

    billygoat777 guest

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    Actually, I'm not sure if it's coolant, but it is a kind of sweet smell inside my car but not outside, I can't quite tell if it smells like coolant though because it is very feint..
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    mooseheadm5

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    Well it could be the heater core or it could be just venting at the tank, which is right at the inlet for the heater system. You should probably find out which.
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    gtopaul

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    Good idea to check the auxiliary fan since this is a common problem on E34s. The aux fan has two speeds and sometimes the ballast resistor will go bad and the low speed won't work. The low speed will come on when sitting at a light or when the A/C is on. I had ro replace this in my sons 93 M5 because it was doing exactly the same thing yours is doing. Whenever I hear your complaint at work the first thing I check is the aux fan.

    Paul
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    mooseheadm5

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    Paul is right about the aux fan. The car shouldn't get hot enough in the winter (guess that depends on where you are) for that to come on in the first place, but without it plus a marginal fan clutch, disaster awaits.

    billygoat777 guest

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    So it may just be a bad resistor? It was on when my AC is on


    I live in San Diego so it's not cold at all
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    mooseheadm5

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    Not a resistor if your fan came on with the A/C.
    Ahh, San Diego. Go visit LaJolla independent and see the cars. If you need work done on the side, contact 94is, she is out there.

    billygoat777 guest

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    Well, the temp didn't go past 1/2 at all since topping off coolant and I auto-xd today, no overheating problems, now I just need to find out if I'm losing coolant or if it "burped" as you said.

    EDIT: how do you go about checking your heater core?
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    mooseheadm5

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    You would want to peek inside the heater case to look for leakage. Not easily accomplished. You can peek at the AC drains for signs of green stuff (under the car above the trans.)

    billygoat777 guest

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    Wow I forgot about this thread, when I was changing my oil yesterday I noticed the AC drain was leaking coolant, so now it's safe to assume that it is really the heater core?

    Whats book time for this job? I would like to do it myself but this seems way too complicated..
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    mooseheadm5

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    Yes, you need a heater core. I don't know the book time, but I'll see what I can find out.

    billygoat777 guest

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    Well my local indy wants as much as I payed for the car for the job. I'm not doin that, can anybody in San Diego help me out with this job?
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    mooseheadm5

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    Contact 94is. She may be up for it.

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