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  1. #1
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    1997 528i Overheating; Fan Clutch, Aux Fan

    Some superb posts on overheating in the forum, but I still have questions.

    At 90k replaced water pump, radiatior and thermostat. This happened during highway driving and was done by an out of town mechanic.

    Now at 102k miles, overheating again; this time in city traffic (I had it towed home).

    Diagnosis so far:

    1. Pulled the thermostat - still overheating. There is a steady increase in temperature from cold to hot while at idle.

    2. Fan Clutch: it is easy to stop (rolled up newspaper) while engine running and temp indicator approaching red.
    a. I've been testing in 50° ambient temperature (engine at idle, hood up, no hot air coming through the radiator). Implied from Jim Cash's posts , at idle there is not enough hot air flowing through the radiator for the clutch to activate.
    b. Is there additional diagnosis?

    3. Aux fan does not come on.
    a. Not sure the A/C test is meaningful with ambient temperature ~50° and lowest A/C setting is 60°
    b. Disconnect the 3-wire connector at the radiator temperature sensor: jumping terminals does not activate fan in any speed. Checking voltage to the connector: none. (Do I read the wiring right - this goes to the relays, activated by the sensor. So problem is before relays and sensors. Correct?)
    c. Fuses (these fuse #s & locations are from the Bentley manual):
    #7, #20, #22 above glove box are fine.
    Looking for #75, fan motor, I don't see any fuses behind the glove box - just connectors. I don't know what a “Jolly Roger” is supposed to look like. The white plastic carrier: how is this removed without breaking anything?
    Trying to check #105 (relay stage 3 fuse) in the trunk: I can't figure out how to get the cover off this fuse box without breaking it.

    Thoughts & suggestions?

    TIA, Charlie
    Cathlamet, Washington
    Charlie Lincoln • Cathlamet, WA • 1997 528i
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  2. #2
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    Your main fan is shot. There IS enough hot air coming through the radiator to activate the clutch even at idle. I used to feel it when I stepped out of the car. If the clutch was engaged there would be hot air blowing on my foot, if not there wasn't. It you blip the throttle slightly you could clearly hear that the clutch was engaged.

    (I saw 'used to' because BMW updated the M52 and M52TU fans to a new common model #. This one is set at a much higher temperature. My factory clutch used to engage all the time, even when KTMP was still at 93C. Since changing it I have NEVER heard it engage since even when KTMP is around 103C. It's still liquidy, not too easy to stop and my gauge never goes north of center but I want an old spec clutch back!)

    Both your fan clutch and aux fan are probably toast (although a full check of fuses etc... is warranted). The main fan alone should be enough to keep the car from overheating in almost all conditions, and if the main fan were to fail the aux fan should kick in to save the day based on independent sensors in the rad. The exception to that would be if the t-stat was stuck closed but if the hoses are hot that's not the issue.

    If you have the same setup as early 1998 528 (with the M52 and three-speed fan) you can bench test the fan with a stout 12VDC power source. I'll have to see if I can dig up the pinouts.
    Last edited by calemon; 05-05-2011 at 10:12 PM.
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  3. #3
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    1 out of 1 members found this post helpful. Yes | No
    Your fan has resistors that the relays switch in and out for the different speeds. It is very common for the resistors to burn out. They are mounted on the aux fan frame. The fuses you mentioned are not in the power control circuit for the aux fan. F75 is behind the glove box, you have to take it out to see it.
    Don't bother with the fuses in the trunk, your problem isn't there.

    Here are the schematics for a '98, yours should be the same.
    Attached Images
    Last edited by jimlev; 05-05-2011 at 08:59 PM. Reason: Added schematics
    Just a few mods.
    If it ain't broken make it better and quicker!
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    Now What?

    Thank you calemon & jimlev. Photos & schematics really help. On my 1997 there is only the one 50 amp fuse; I don’t see a #76.

    Finally, a weather window to work outside again. Just to make sure, I pulled the water pump – all seems ok with it – and ordered new fan clutch and spare thermostat (& gaskets).

    Still trying to diagnose aux fan. I still don’t know if it works or not, but it appears that power is not getting to it.

    The 50 Amp fuse is fine. However I am not getting any voltage to it, even with engine running. Fuse #105 is ok too. I’ve checked this two ways: DVM to check for voltage at #75 (none) and, with battery disconnected, resistance check between Fuses #75 and #105 (open circuit).

    I have trouble visualizing how I might have a severed wire without a big short circuit. Please tell me I’m doing something wrong. Where do I go from here?

    - Charlie
    Charlie Lincoln • Cathlamet, WA • 1997 528i
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    Fix your Aux fan issue as mentioned.

    However, any item in the cooling system that has NOT YET been replaced: replace them ASAP before you regret.
    - Thermostat in general lasts about 60-70K and that is it.
    90K is way overdue.
    - Ditto for Fan Clutch: Sachs or Behr ONLY!
    5 years on Sachs, no issues.


    I wrote this DIY for my 1998 528i back in May 2006, and so far so good.
    (Edit: Do NOT use MTC Fan Blade, it broke in 1 year, use BMW Fan Blade only).
    Delete the "hyphens" to see the link:

    http://www.b---immerboard.com/forums/posts/199986
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    Abridged Version Aux Fan Resistor DIY w/ pictures

    Charles,

    Here's an abridged writeup (let me know if you want the full version), strictly for replacing only the aux fan resistors. There usually really is no need to replace anything else, as in most people I know who have the problem you are describing only need the resistors (though I am wondering about your comment that you are getting no juice at the resistors):

    Abridged Version Aux Fan R&R for 1996 e39 BMW 528i (pictorial w/ comments):



















    Hope this helps. Total cost of this job was only the aux fan resistor repair kit, which was like $55-$60 at the time I did it a few years ago.
    Last edited by eurodavid; 05-22-2011 at 05:20 AM. Reason: correction
    EuroDavid
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    Quote Originally Posted by charleslincoln View Post
    Thank you calemon & jimlev. Photos & schematics really help. On my 1997 there is only the one 50 amp fuse; I don’t see a #76.

    The 50 Amp fuse is fine. However I am not getting any voltage to it, even with engine running. Fuse #105 is ok too. I’ve checked this two ways: DVM to check for voltage at #75 (none) and, with battery disconnected, resistance check between Fuses #75 and #105 (open circuit).
    Charlie, the reason you are not getting any reading from F105 to F75 is because you have relay K201 contacts between these 2 fuses.
    That relay needs to be energized to supply 12 volts to F75.
    Have you checked F22 that supplies power to K201's coil? If the fuses are all good, the relay is probably your problem.
    My car doesn't use the same set up as yours, so I don't have any of the relays that your car uses for the 3 fan speeds.
    That relay is either behind the glove box or under the hood in the DME box.
    Once you find that you have 12 volts getting too the fuse make sure that all 3 speeds work.
    Let us know what you find.
    (Euro, I was hoping you would see this and post the pics for the resistor fix)
    Last edited by jimlev; 05-22-2011 at 08:13 AM.
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  8. #8
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    Now Aux Fan

    Since my last post: Quicker and less expensive to buy another car, of a vintage I understand; now driving an 1988 Peugeot 505. As to the 97 528i (12/96 build date – 3 speed aux fan):

    1. Fan Clutch replaced – that resolved the immediate overheating issue.

    2. K201 relay replaced – see later comments. Another note on the K201 – it is not a normal stock item at most of the BMW aftermarket sources. Pellican parts had the best response, and price after factoring shipping (USPS priority mail).

    3. Aux Fan is still not working.

    Further Aux Fan diagnosis:

    1. Disconnecting the fan plug and using a direct battery source, the fan works on all three speeds.

    2. Retest jumping the wires at the radiator temperature switch. (Voltage at the relays: I do have battery voltage at pin #s 30, 85, 86.) Ground at temp switch connector is good; battery voltage is available at the relay feed wires; jumping the relay wires to the ground did not activate the aux fan.

    3. Jump the relays (K21 & K201) pin #87 & #30. Aux fan works in both cases.

    Is it possible that both the K21 relay and the new K201 relay are defective? How do I test the relays themselves before ordering more?

    Am I missing something simple that should be obvious?
    Charlie Lincoln • Cathlamet, WA • 1997 528i
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  9. #9
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    Relay Test

    Is this an appropriate relay test?
    Apply 12v to terminal #86, ground #85. Should hear click and have continuity at terminal 30 & 87.


    If so, my relays are OK and there is something else going on that I don’t understand.
    Charlie Lincoln • Cathlamet, WA • 1997 528i
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    That is the correct way to test the relay.
    Pull the relays out of the sockets and see if you have 12 volts going to the location that all the relay pin #30's plugs into.
    First make sure that fuses F7 and F22 are good.
    There should always be 12 volts at those points. If you don't have 12 volts there you have other problems.
    Let us know what you find.
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  11. #11
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    It is working

    Following Jim’s most recent advice: I removed the relays and checked the sockets for voltage at pin 30 (present); I also had voltage at # 86 with ignition on.


    Contemplated the wiring schematics again - and concluded the problem is me. Once again, at the dual temperature switch connector, jumped the # 85 wires to the ground wire. Note those pin sockets on the connector are very small; to small for the dvm probes to make a good contact. So with a smaller probe the aux fan sprung to life.


    The remaining problem now has to be the dual temp switch - when the fan clutch failed, this must be why the aux fan didn’t bail me out. (its the only reason left, right?)


    Thanks so much for all the help, and I apologize for not doing the diagnosis right in the first place.
    I'll post a recap after I replace the temperature switch and test the old one.
    Charlie Lincoln • Cathlamet, WA • 1997 528i
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