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Thread: M5 overheating at idle and in traffic.

  1. #1
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    M5 overheating at idle and in traffic.

    Hello All, I am a long time reader of this forum but have not posted in a while. I purchased an e34 M5 nearly four months ago. I absolutely love this car. It is my second E34, the previous being an 540/6. I am having one problem with the car. It is overheating after idleing for a long time (e.g >10 minutes) and also overheating after being in traffic for more then 10-15 minutes. I have noticed a lot of dirt and debris in the coolant reservoir, could this be causing this problem? (if so how could i remedy it?). I was told it could be the auxillary air fan, which i dont believe i hear kicking in. Any ideas on how to begin addressing this problem is appreciated.

  2. #2
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    It a bad fan clutch. I have a brand new one (s38 specific) in box for sale. PM me.
    Last edited by NikosX; 05-01-2011 at 06:40 PM.
    ________________________________
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  3. #3
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    bad fan clutch?
    Desertpir8 - '92 535iM - '62 M-B Unimog - '03 VW Jetta TDI

  4. #4
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    Your car is so SMOKING HOT it overheats because of it's sheer sexiness?

  5. #5
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    ha ha ha...thanks very much guys. I'll look into the fan clutch...

  6. #6
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    Fan clutch should engage when the car reaches operating temperature and above 50-60 degrees ambient temp. Just about anytime I drive it around town, I can hear the fan. The car should, unfortunately, sound like a school bus until the RPM's get above 3k or so, and then the fan should disengage. Also, you can hear the clutch engage the fan when sitting still as the engine warms. The car will sound normal, and then you'll hear a "whrrrrrrrrrrrrrrrrrr..... sound spooling up from the engine. That's the clutch engaging.

    The test for the aux fan is simply to turn on the a/c as that engages the "high" speed regardless of the operating temperature of the car. The low-speed can also be tested by bridging the leads on the underhood relay.
    Last edited by TouringDan; 05-02-2011 at 06:03 PM.


  7. #7
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    On top of what's listed..thermostat might not be opening all they way.

  8. #8
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    Had an issue with the thermostat on my V***o ... It opened up too slow.. Computer was going apeshit crazy and the moneypit light was so bright it gave me a tan

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  9. #9
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    Typical of a bad aux fan. I've replaced a few of them because of the same symptoms. Put the AC on while it's running and see if the aux fan is turining in low speed mode.

  10. #10
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    Buddy im in the same position right now. if you love this car replace the thermostat, its ten bucks and takes 20 min to do. Then make sure your fan is engaging properly, after all that ive found my water pump to be the culprit. It could be the oem plastic impeller fins... I will diagnose tomorrow.

  11. #11
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    How hot is it running when you say its overheating?

    For starters if you have debris in the reservoir you should consider a coolant flush... places like jiffy lube can do that for you if you are unable to do it yourself.

    Checking the clutch fan is a good idea.

    I wouldn't have thought the aux fan would make much of a difference when its this cool out, mine doesn't (535 though).

  12. #12
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    I don't think That little tiny fan all the way in the front of the car is going to do Much of anything let alone cool down an engine.

  13. #13
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    Check the aux fan its simple and sounds like your issue but if you have debris in the system you should do a flush at the least.

  14. #14
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    Quote Originally Posted by ChiTownTy View Post
    I don't think That little tiny fan all the way in the front of the car is going to do Much of anything let alone cool down an engine.
    Wait until it's not working then you'll see how important it is to have it operational.

  15. #15
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    thanks for the all the advice. I'll check the aux fan and thermostat as well. As for the coolant flush, i am wondering if a flush will remove all the debris in the reservoir-I mean is pressure applied to get rid of all the grime?
    Last edited by 540ii; 05-02-2011 at 11:41 PM.

  16. #16
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    How much grime are we talking about?
    ________________________________
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  17. #17
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    Quote Originally Posted by gtopaul View Post
    Wait until it's not working then you'll see how important it is to have it operational.

    Mine was seized when I got the car, ran it that way for a year, made no difference, however as stated its a 535, plus I should add the AC was non functional at the time, and the clutch fan works as it should.

    If you are concerned about the debris in the reservoir, remove it and wash it out, (if its removable). If debris is in there its in the rest of the system and could actually be clogging up the rad, imo the rad really needs flushing, and yes pressure is applied.

    Look the way I see it, the issue could still be the thermostat the pump or the rad etc., however you have told us there is crap in there, that has to be cleaned out, so do that first, if your problem goes away you're done, if not at least you have taken care of one of the contributors of inadequate cooling.

    Prior to refilling with new anti-freeze carefully inspect all cooling hoses and replace where necessary.

  18. #18
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    Quote Originally Posted by bolloc View Post
    Mine was seized when I got the car, ran it that way for a year, made no difference, however as stated its a 535, plus I should add the AC was non functional at the time, and the clutch fan works as it should.
    You're in Canada and it's not an M5. Try that in the South with the AC on and you won't last long.

  19. #19
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    Even without the A/C, there are times in traffic where I've heard the aux-fan engage and it definitely made a difference. The S38's generate a LOT of heat. Every little bit helps.

    The fact that your car is cooling somewhat but eventually is overcome by heat speaks of reduced cooling capacity through heatsoak. The car can't shed the heat generated fast enough. Were it my car, I'd immediately look into the radiator and the fans. If the thermostat has a broken spring or wasn't opening, you'd know it because it wouldn't keep cool at all - it would just rocket right past the midpoint and go directly into the money-zone. Same with the water pump.

    There are a lot of things that can cause any car to get hot, and all of them should be checked out. How is your fan shroud? Missing pieces from the shroud can have an effect on the efficiency of the fans. Even though these things are supposed to be self-bleeding, I've found that on my car, this isn't the case. There's a little stainless bullet looking thing up by the firewall and the heater aux pump. That's the OEM bleeder valve. If your heater isn't blowing hot, you've got air in the system somehow.

    Grime in the tank is something that you should address, and I'd also think about a radiator flush if this is the case. Another thing to check is the forward-facing surface of the radiator itself. I've seen them so clogged with dead bugs and grime that the cooling capacity of the radiator is severely compromised. T-stat is another thing if it is only partially open, and depending on the mileage it may be worth replacing anyway to avoid headaches later down the road. You can tell if the t-stat is opening by using a laster-thermometer on the upper and lower hoses. If the car is fully warmed up, the differences should be apparent. If the bottom hose is stone cold and the upper is screaming hot - the thermostat should be suspected as well as the radiator itself. An indisputable test can be done by removing it from the car and sticking it in a pot full of water on the stove with a thermometer and seeing if it opens at the correct temperature. In my opinion, however, if you've got the old one out - don't bother putting it back in. Just replace it. The water-test is handy with the new one and I always test my replacements pre-install.

    The water pumps on these cars were not of the plastic variety unless a previous owner cheaped-out on the OEM replacement, so the worries associated with the plastic impellers can be eliminated. However, that doesn't mean the pump itself is ok. Usually, they start to whine, grind, weep, or all three when they go south. It's a fairly simple replacement if this is the case. If the pump has outright failed, I guarantee you'd know it IMMEDIATELY as you'd be deep into the red zone within minutes of driving.

    Like I said earlier, if the fan clutch is good, you'll know it immediately due to the sound that the fan generates when coming off-idle and up to about 2500 RPM's. I'll take a video of mine and post it later today. Also, the "paper test" cited by some is a worthless exercise, IMHO. Even the newest fan clutch can be overcome by sticking a rolled up newspaper in the fan while engaged.
    Last edited by TouringDan; 05-03-2011 at 09:35 AM.


  20. #20
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    Quote Originally Posted by NikosX View Post
    It a bad fan clutch. I have a brand new one (s38 specific) in box for sale. PM me.
    is there a difference between a m5 and regular 525i fan clutch?

  21. #21
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    Yes, but it is the same as the 535
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  22. #22
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    My M5 started doing this yesterday as well. Idling or stopped, the water temp needle would creep to ~3/4 and bob around a wee bit. Never went past 3/4. Once moving, back to 1/2 mark. Hammering at 90mph on country roads, also dead straight at the 1/2 mark. I parked it for now until I have time to investigate.

    The fan clutch was just replaced a month ago, I'll give it another check tonight and post my findings. It's mechanical so there's always a chance it's failed again. Who knows, maybe there's a dead bird stuck in there.
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  23. #23
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    Quote Originally Posted by gtopaul View Post
    You're in Canada and it's not an M5. Try that in the South with the AC on and you won't last long.
    Yeah I know I am in Canada, and I assumed that the OP is also in Canada based on his location and that is where most of his driving takes place, I also assumed because I only live 100 km away that he hasn't needed his AC for the last 4 months which is the length of time he has owned the car.

    I also realize that he has an M5 and I don't, that's why I mentioned what mine was, there could be enough of a difference that warrants the use of the aux fan in his car during the winter or in temperatures that we have been experiencing, I doubt it very much though.

    I believe we take care of what is obviously wrong first, before we start randomly throwing parts to solve the problem, I wouldn't be at all surprised if the aux fan didn't even come on during the cold weather, (haven't bothered to check if mine does or not). The OP expressed concern about the debris in the system, clean that up and go from there.

  24. #24
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    Quote Originally Posted by bolloc View Post
    Yeah I know I am in Canada, and I assumed that the OP is also in Canada based on his location and that is where most of his driving takes place, I also assumed because I only live 100 km away that he hasn't needed his AC for the last 4 months which is the length of time he has owned the car.

    I also realize that he has an M5 and I don't, that's why I mentioned what mine was, there could be enough of a difference that warrants the use of the aux fan in his car during the winter or in temperatures that we have been experiencing, I doubt it very much though.

    I believe we take care of what is obviously wrong first, before we start randomly throwing parts to solve the problem, I wouldn't be at all surprised if the aux fan didn't even come on during the cold weather, (haven't bothered to check if mine does or not). The OP expressed concern about the debris in the system, clean that up and go from there.
    Checking the aux fan doesn't take any parts and I can tell you even on a cool day here and the altitude thrown in (Harder to cool) the aux fan definitely make a difference. As long as the OP air conditioning works the aux fan will come on if it is in good working condition. But you're right the he needs to clean out his cooling system.
    Last edited by 93FIM5; 05-03-2011 at 05:27 PM. Reason: Clarification

  25. #25
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    Quote Originally Posted by CrashTest View Post
    My M5 started doing this yesterday as well. Idling or stopped, the water temp needle would creep to ~3/4 and bob around a wee bit. Never went past 3/4. Once moving, back to 1/2 mark. Hammering at 90mph on country roads, also dead straight at the 1/2 mark. I parked it for now until I have time to investigate.

    The fan clutch was just replaced a month ago, I'll give it another check tonight and post my findings. It's mechanical so there's always a chance it's failed again. Who knows, maybe there's a dead bird stuck in there.
    Every properly running M5 I've sat shotgun in or drove always ran one needle width to the left of straight up unless it was being hammered on a track day and, then it might hover at straight up 12 o'clock position.

    You might want to give your system a quick once over as it appears yours is running just a bit on the warm side.

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