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Thread: Fan clutch repeated failure

  1. #1
    Join Date
    Apr 2021
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    2006 330CI ZHP, 2000 750

    Fan clutch repeated failure

    Hi everyone,

    My 2000 750iL has been having persistent, confusing cooling issues somehow relating to the fans.

    I live on a fairly steep hill which involves 1-2 miles of low speed (30mph or less) uphill driving.

    Today is the first day of warm weather this year, and the 750 began overheating when driving home because the fan clutch did not engage. The coolant temp kept creeping up and the needle shifted beyond the center point just as I was pulling into the driveway.

    I shut the car off and opened the hood for several minutes. Upon starting the car again, the fan clutch engages immediately and exactly as it should and the coolant temp drops like a rock down to the correct temperature.

    I have replaced the fan clutch 3 times now. First 2 were the Mahle OE parts and this last one was a genuine 750-specific fan clutch. The last fan clutch was no good in this exact same way. I did not mess with the bimetallic strip or try and modify the clutch in any way. The fan blades have been replaced.

    I have replaced the expansion tank (Genuine), thermostat (Mahle), radiator (Mahle, upgraded M5/Z8/Hot climate package unit) and many of the hoses. As I said before, once the fan engaged, things seemed very, very normal and there are no issues at highway speed.

    The electric fan always seemed to be running at full speed any time the car is warm and going slowly uphill/stopped. It seems kind of wrong but I have no frame of reference. It will get up to 230F at idle/drive thru but cools right off once you're moving. I rarely notice the mechanical fan.


    So what am I missing? Getting a 4th fan clutch in 15K miles or so just doesn't seem right. I believe the engine is running pretty well, it's smooth as butter and gets 20/21 MPG on the highway. I've done O2 sensors, mass air flow, ignition system, intake gaskets, and so on. Even if it wasn't running great, I would still expect the fan to engage



    Any and all insight is appreciated.

    Thanks,

    Evan

  2. #2
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    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
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    Quote Originally Posted by Timm View Post

    Timm- thanks so much for the response, your videos are incredibly helpful, methodical and clear- I've watched many of them over the years. I did check for any massive airflow blockage a while ago, but there wasn't anything alarming to be found.



    I did go ahead and pull off the bumper this afternoon and sprayed out the condenser anyway. There was more junk in there than I thought, it was certainly a worthwhile endeavor. No huge clumps of junk like in your video, mostly bugs. I can feel the air from the aux. fan a little more now in the engine bay- and the temps seem to be slightly lower around 25-40mph.


    Unfortunately, the fan clutch still only engages after shutting off and restarting the engine, and the thing just seems to struggle to stay cool at low speeds, even though it was only 72F outside today.


    I drove up into the mountains- 8% grade, extremely winding, and no more than 25mph the whole way. Got a little more than 2 miles up and the coolant temp was at 232-234F and still creeping upwards. I pulled over, verified the fan clutch was not engaged with newspaper, and shut it down. Re-started about 2 or 3 minutes later- the fan clutch engages about 5 seconds after the car starts- no "whoosh" as it's starting- but the thing cooled down in a hurry with both fans- as it should. Tons of airflow when the mechanical fan is running.

    Kept going uphill, coolant temp quickly went down to 212F or so, then the fan clutch disengaged (probably because the thermostat closed?) and the temps crept up to 235F or so again- no sign of mechanical fan- until I stopped. Exactly like the first time, stopping and restarting the engine somehow got the fan clutch to engage.

    The first Mahle fan clutch leaked out after 10K miles or so, the second one seemed to have this exact same failure mode.




    See this clip of the aux. fan running- it will pretty much always sound like this when idling after warm up, and all the way up the hill.




  4. #4
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    Sorry you're dealing with this. I know how frustrating this can be, because I dealt with a similar issue with my 85 Mustang for a couple years before finally diagnosing it. Let's see if we can work through some diagnostic steps.

    My initial gut reaction to what you are describing is that the fan is not sensing heat from the radiator. This can either be that the cooling system is improperly bled (air in system and radiator), it is low on coolant (air in radiator), or the water pump or thermostat is not allowing fluid to circulate adequately (cold radiator).

    I say this because the thermostatic clutch for the fan must sense hot air from the radiator in order to engage. If you hear it engage when the engine is first started, that's a good sign it has oil and is ready to do its thing. They engage after a start, because the oil gets to settle in the clutch from it not turning. When the engine first spins, it take a few seconds for the oil to sling to the outside of the clutch, which disengages it if the temperature is low.

    Do you have one of those infrared thermometers? What you want to do is measure the temperature on the back side of the radiator facing the fan once the engine is fully hot. Then take measurements after you replicate the "overheating" scenario. This will let you know if the radiator is actually getting hot and if you notice a difference. Use that temp gun to measure different parts of the radiator to see if it is uniformly hot.

    You replaced the radiator, expansion tank, and thermostat. Did you get the cooling system fully bled? Replacing all that stuff means there was plenty of coolant drained out and air allowed in the cooling system that will need to be displaced and replaced with fluid. There is the "proper" BMW way to bleed it with the bleed screw, which makes a mess and wastes coolant. The way I fill my system is to hook everything up tight, except the upper radiator hose. I fill my radiator up through the upper neck until coolant runs out and then through the upper radiator hose until it is full. This gets 90% of the air out, since as you fill, the air can escape through the highest point in the system. Then I start the car and let it warm up with the cap off while watching the level inside. Turn on the heat inside to full hot (this will open the heater control valve). The car should not be getting hot enough to blow steam everywhere nor will it be under pressure with the cap off. It'll slowly heat up until the thermostat opens, at which point it'll suck a ton of the coolant in from the expansion tank. I then top up the expansion tank at that point and drive it around the block a couple times with RPMs getting above 2k before letting it cool down. Once the engine is cold, remove the cap and top up the last bit. That gets me right to an air-bubble-free cooling system.

    Let us know what you find.
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  5. #5
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    Quote Originally Posted by racer2086 View Post
    Sorry you're dealing with this. I know how frustrating this can be, because I dealt with a similar issue with my 85 Mustang for a couple years before finally diagnosing it. Let's see if we can work through some diagnostic steps.


    Let us know what you find.
    Thank you for your detailed response.

    The fan typically does not make any big sound at cold start- not like my E46. The replacement fan clutch 1 (leaker) would engage at cold start for a while until it leaked out too much. It was quite noticeable. The second Mahle clutch and this genuine one do not make any big "whoosh" sound EXCEPT the first or second time after being removed from the car- even though I try to store them near-upright to try and avoid leaks. Mahle replacement #2 never leaked, nor has the genuine clutch #3.

    There was a period where an overflow hose with a small leak which could have drawn some air in. That has been resolved for a few thousand miles with a genuine hose and correct hose clamp. Have bled this car and other BMWs with no issues. Coolant level is stable and the pressure test shows no leaks at this time.

    Moral of the story: I will bleed it again tomorrow morning to see if I am making a fool of myself


    When I pulled over at 234F, the upper radiator hose was properly hot and the lower one was not quite as hot. The aux fan does move a good amount of air at full speed and the air was piping hot.

    When the fan clutch was working, the lower hose cooled down considerably as tons of air was sucked into the grilles- got out of the "kinda overheating" 234F range almost immediately and seemed normal enough for me to continue further up the hill to continue the experiment. Coolant temp went down to 205 or so, fan clutch disengaged and we were back to square one.


    An infrared thermometer is definitely a good idea- don't currently have one of those, but not for long!


    My impatience and frustration, combined with the lack of big "whoosh" at cold start have convinced me to buy a new E65/E53 fan clutch with the heavy-duty fan blade. Aside from the possible fitment quirks it seems like an overall upgrade in terms of durability and airflow.


    This seems like a pretty much exact match for my situation which nudged me toward that decision- fixed with an E65 clutch: https://www.bimmerforums.com/forum/s...perating-temps

    Since this story is so similar to mine, and I have already spent tons of time and money on this car that I am willing to try it. I've already had one definitively bad clutch on this car and two on the E46, all in the last 2/3 years.


    I will be sure to report back with any update.
    Last edited by evankirkhart; 06-18-2024 at 01:58 AM.

  6. #6
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    I switched to this fan and clutch on my M62TU a few years ago. Works great. Very happy with it. Also works for e38s. (Not sure about the V12.)

    https://www.bimmerforums.com/forum/s...or-V8-e39-cars
    Last edited by R Shaffner; 06-18-2024 at 12:47 PM.

  7. #7
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    Quote Originally Posted by R Shaffner View Post
    I switched to this fan and clutch on my M62TU a few years ago. Works great. Very happy with it. Also works for e38s. (Not sure about the V12.)

    https://www.bimmerforums.com/forum/s...or-V8-e39-cars
    It works for the V12 as well. Tighter spacing for the shroud, has to come up a bit.

    https://www.bimmerforums.com/forum/s...-clutch-in-E38


    Sent from my iPhone using Tapatalk

  8. #8
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    Yeah, I put the E65 fan on my wife's E39. I haven't noticed any performance difference. Still locks up and acts like the OEM one. Test the radiator temperature with the infrared gun. It'll be interesting to see what it reads because either the fan clutch is bad or the radiator isn't getting hot to engage the clutch.
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 303k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 128k
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  9. #9
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    I have seen internally clogged radiators cause this issue. Get a new BEHR radiator if you find the radiator to be the cause. The fan clutch is purely mechanical and I am surprised it would fail that quickly but anything is possible.

  10. #10
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    Cool Fixed!

    I'm happy to report the new fan & clutch completely and totally resolved my issues. Upon closer investigation, the old replacement fan clutch (3-4k miles on it, genuine part no 11527500339, 750 specific part) was already leaking oil from the bimetallic strip. Absolutely baffling, I wish FCP Euro would take my concerns more seriously and send these parts back to Mahle for investigation. On another note, the fan clutch on my E46 (3rd or 4th replacement in 4 years, genuine) has also decided to completely leak out from the same place over the course of ~18 months.

    On the same steep, slow uphill, the coolant temp hovers very close to 225 as the thermostat opens and closes. Fan clutch engages right when you'd expect it to. The fan seems somewhat quieter, perhaps its maximum rotational speed is a bit lower too- but tons and tons and tons of air, noticeably more than the old-style fan. Every aspect of the fan/clutch seems to be heavier duty which gives me hope it will last longer.

    The aux fan goes out of high speed a few seconds after the mechanical fan kicks on. All seems very, very normal and as-designed, this road is a cooling system stress test considering the 6-8 percent grade and low speed.

    Finally made it to the top of the Santa Ynez mountains (~4000' elev.) uninterrupted without even a hint of overheating or cooling issue. Highly recommend this fan/clutch anyone who has experienced fan clutch issues even after replacement.

    On to more interesting projects, and less worry about coolant temperature! Thanks to everyone for your input and advice.

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  11. #11
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    Same setup here - got the E65 fan and clutch in my E38 back in Aug. 2023.
    Long trip after that was AZ-IL-SC and back to AZ.
    I see you're from CA.
    A week ago I drove... Phoenix - Kingman, AZ and took I-40 to LA and down to Santa Monica.
    All good, no issues even in the hot desert, high elevation. Cooling system was done in 2020.
    It's a joy to get into the 20th year of ownership of this car even though it comes with 'high maintenance' on her part but it's worth it.

  12. #12
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    Nice to hear you resolved your issue. I wonder what other “improvements” can be made by using other E65 parts on our cars frequently.

  13. #13
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    Quote Originally Posted by Btkeenan View Post
    Nice to hear you resolved your issue. I wonder what other “improvements” can be made by using other E65 parts on our cars frequently.
    Well, some of us have put the larger 4.8 N62 throttle body on our M62TUs (from an e60). Most of us think it helps a little.

    Other mods I've made on my '02 540i with parts from other BMWs include an 88C thermostat and a 1.4 bar expansion tank cap.

  14. #14
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    Quote Originally Posted by R Shaffner View Post
    Well, some of us have put the larger 4.8 N62 throttle body on our M62TUs (from an e60). Most of us think it helps a little.

    Other mods I've made on my '02 540i with parts from other BMWs include an 88C thermostat and a 1.4 bar expansion tank cap.
    Nice. I've done a few retrofits from E39s also like auto headlights and updated GDO to work with modern garage doors.
    2001 BMW 740i | 2013 Ford SVT Raptor | 2018 Mazda CX-5 Touring AWD

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