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Discussion Starter #1
Hello to all who's reading,

I have a question about cooling and overheating.

I have 03/2000 E39 M5 with 126,000 miles (about 202,000 km). Over all car has no issues. However I've started to notice that its running hotter than normal in some cases. Most of the time the temp gauge is right in the middle (48-50%, maybe 1-2 mm to the colder side (11:58), but pretty much in the middle). However if the outside temp reaches 90+F (about 32+C) and I'm sitting in the traffic with A/C running, the temp gauge would reach the 2nd dot (which I guess is about 75%). As I start moving temp gets back to normal shortly after. (kind make sense; car could be taking hot air or exhaust heat from the surrounding cars / etc).

Yesterday, outside temperature reached well over 100F (37.7C). I got stuck under the sun in the major traffic jam for good 45 min. (also my car is black, which makes it even more hotter). The outside temp was between 116-118F (46.6-47.7C). Cars were bumper to bumper, so no air flow. Just heat from cars / exhausts. Again, A/C was running and the temperature gauge reached the 2nd dot and even went 1mm pass it. (75%-80% hot). Once the temp gauge reached the 2nd dot, I would turn off A/C and with minutes car goes back to normal temp. Turn A/C on, 5-10 min later, temperature gauge error would start getting to the 2nd dot. And so on. (Keep in mind, all this was happening while I was pretty much parked along with 100's of other cars. (spend about 30 min driving 1-2 miles..................probably could have walked faster).

Finally after I go out the traffic, I went for a mountain highway drive; temp was back to normal. As soon as I started to drive heavily with sport mode ON, going up hill, through mountain corners with RPMs between 4.5K-6.5K RPM (Mainly 2nd and 3rd gear), car started to get hot again and this time it actually came close to red line on the temperature gauge. Immediately I dropped the RPMs, turn the head full blast, and with minutes temperature gauge went back to normal and stayed normal for the rest of the drive.

Does that sounds like a water pump going out?
I thought that E39 M5 pumps rarely go out as they are metal and not plastic like E39-none M Cars. Also I do not see any leaks. Coolant level never droppers and clean blue color. I just can't think of anything else. I was planning to drain the coolant and refile with new, since it was never done. (I was told by a local dealer that the coolant in E39 M5 is for the life of the car and should not be drained).

I know its not my fan, as I know it works. It comes on & off temperature gauge. OEM BMW Thermostat is fairly new, I installed it about 2 years ago (about 7K miles) with OEM BMW top & bottom sensors.

Any suggestions?
 

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I would triple check the aux fan and the mechanical fan clutch and then look for debris blocking the radiator. If the water pump wan't working the temp would not go down. You are describing a classic airflow problem.





PLEASE NOTE THAT I DO NOT OWN AN M5 AND THIS POST IS NOT INTENDED TO BE ARROGANT. PLEASE READ THE IMPORTANT REVISED DISCLAIMER THAT APPLIES TO THIS POST
 

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Discussion Starter #3
Any suggestions on how to check the fan / fan clutch?
I know that when its hot, fan is running pretty heavily, so I would assume that its functional.............................and that's where my knowledge ends. (i'm clearly way too knew at this).
 

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Probably a good idea to remove the fan assembly completely, b/c my indy just replaced my temp sensors, radiator, and rad fan and found enough debris for a rat's nest...so cleatly u could very well have a blockage problem...and she runs even cooler than norm on an average day!
 

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Finally after I go out the traffic, I went for a mountain highway drive; temp was back to normal. As soon as I started to drive heavily with sport mode ON, going up hill, through mountain corners with RPMs between 4.5K-6.5K RPM (Mainly 2nd and 3rd gear), car started to get hot again and this time it actually came close to red line on the temperature gauge. Immediately I dropped the RPMs, turn the head full blast, and with minutes temperature gauge went back to normal and stayed normal for the rest of the drive.
I would have said clutch fan since you can hear the aux fan running hard, except that the above statement makes me think it might not be a fan problem because you were overheating badly while going, what, 40 to 80 mph? There should have been lots of air flow at those speeds even if neither fan was working. So maybe debris in the rad and condenser fins.
 

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Discussion Starter #7
I'm going try to do both. Test the fan (not with my fingers.........:) ) and clean out any debris.

Thanks guys. I'll post an update with results. (Maybe in couple weeks).
 

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Discussion Starter #8
Well, tested my car today, and its the fan clutch. I rolled small magazine in to a tube and it used it to stop it while it was spinning. It stopped as soon as the tube touch the blade. Just like in the link above, except I used the magazine vs my fingers. :)

Thanks everyone for the help & links.

PS: if anyone has a good link on how to replace the clutch fan, i would greatly appreciate the link(s).
 

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Just to be clear, the clutch doesn't start to lock up until the air coming through the rad is 95 deg C, so if you did this test at idle and with a coolant temp less than 95, a rolled up paper will stop the fan.
 

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are you sure you tested the fan clutch correctly?
 

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Just to be clear, the clutch doesn't start to lock up until the air coming through the rad is 95 deg C, so if you did this test at idle and with a coolant temp less than 95, a rolled up paper will stop the fan.
Agree with this statement. I would drive the car around a bit and test the fan clutch again to ensure you are doing the test as close as possible to the temps you experienced. If operating correctly, at operating temps the newspaper/magazine should not stop the fan clutch.

Also, check out the DIY section for a post I did regarding the aux fan replacement. Yours may be working, but you'll be surprised at how much debris sits behind the center unit of the aux fan that can be cleaned out with the aux fan removed.
 

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Discussion Starter #12
I tested the fan clutch after spending about 25-30 min on the road. (city driving / drive home from work).
It was not too hot outside, maybe 70 - 75 F, the roads were still fairly wet and it was extremely humid (massive rain passed about 1 hour before I started to drive), but I was still running A/C (it was set to 78-F / Auto).
The temp gauge was pretty much in the middle, maybe 1-2 MM to the left (11:58). As soon as I pulled in the garage, I opened the hood without turning off the car, and did the test. With barely any pressure from the rolled up magazine, the fan stopped.

So did I do it right?


PS: I actually did not drive the car today, as I read on line that a fan with a bad fan clutch, can become loose and fly off which driving. And that's a little scary. I will also check DIY links RE: cleaning derbies, etc.
 

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I tested the fan clutch after spending about 25-30 min on the road. (city driving / drive home from work).
It was not too hot outside, maybe 70 - 75 F, the roads were still fairly wet and it was extremely humid (massive rain passed about 1 hour before I started to drive), but I was still running A/C (it was set to 78-F / Auto).
The temp gauge was pretty much in the middle, maybe 1-2 MM to the left (11:58). As soon as I pulled in the garage, I opened the hood without turning off the car, and did the test. With barely any pressure from the rolled up magazine, the fan stopped.

So did I do it right?


PS: I actually did not drive the car today, as I read on line that a fan with a bad fan clutch, can become loose and fly off which driving. And that's a little scary. I will also check DIY links RE: cleaning derbies, etc.
No, you still weren't hot enough. 12 o'clock on the gauge is around 90C. The clutch starts to engage when the temperature of the air flowing over it from the rad reaches 95C. Keep in mind, the clutch fan is the back-up fan on an M5. The aux. electric fan is the primary fan. Only when it's overloaded does the clutch fan kick in.

I think you'll find the exploding fan blades were all caused by the clutch locking up solid so the fan speed got too high. If your clutch is still spinning freely, you don't have to worry about this.
 

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Are you able to pull codes? I bet you [also] have a code 69.
 

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Discussion Starter #15 (Edited)
Yes, I'm able to pull codes. I normally don't do it unless SES come on, but I will do it when I get home. Last time I've see 69 "Engine coolant temperature, Plausibility", is when my MAF's were going out, but I was getting tons of codes at that time.

I'm going to take my beast back on road in the couple of days and I will turn KTEP (test #7) to get actually temps. I think Thu / Fri should be very hot, so getting the car up to 90-C should be no issues.

Also, I just wanted to make sure we were talking about the same fan.
There are 2 fans;
#1 - is the Main Fan, that is near the Engine Block (Fan 11 blade - part #11521712110). That's the fan that has a fan clutch, and that's the same fan I tested with rolled up magazine.
#2 - is the Aux Fan, that is near the front grille (Pusher fan - part #64546921395). That fan is also running, but I have not tried to test it by stopping with a rolled up magazine. (I think its just an electrical driven fan that works as a backup for the main fan................am I correct?)
 

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Also, I just wanted to make sure we were talking about the same fan.
There are 2 fans;
#1 - is the Main Fan, that is near the Engine Block (Fan 11 blade - part #11521712110). That's the fan that has a fan clutch, and that's the same fan I tested with rolled up magazine.
#2 - is the Aux Fan, that is near the front grille (Pusher fan - part #64546921395). That fan is also running, but I have not tried to test it by stopping with a rolled up magazine. (I think its just an electrical driven fan that works as a backup for the main fan................am I correct?)
Yes, #1 is the "main" fan, although technically it's the backup fan. The fan is mounted on a slipping clutch #2 that slips when the air temp is less than 95C. That's why you can stop the fan with the paper. When the temp gets above 95C, the clutch locks up, quite abruptly in my experience, and the fan then spins at the same speed as the pulley, #4. It starts to slip again as the rpm increases above a certain limit so it doesn't overspeed and explode.

It's not a mechanical clutch, it's a fluid clutch. It uses a silicone fluid that is directed through ports depending on the temperature acting on a bi-metallic coil.

The electric fan is the main fan. It kicks in at a much lower temp, around 74C in the lower rad hose. It does the primary air moving until the heat load gets too high and then the clutch fan kicks in to back it up. Its speed is varied by the DME depending on heat load. No, you can't test it like the clutch fan.
 

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Discussion Starter #17
68FB...............I don't know how to thank you. I just learned so much from your write-up.
Well, I think I'm going have wait couple more days until this cold front moves. Its been none-stop raining, plus today it was a high of 60-F.

So hopefully I'll be able to get to testing next week, as the weather should come back to 80's-90's-F. But I have a feeling that I just need to clean the derbies, and that may solve the issue. I'll be sure to post an update after testing.
 

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You got the fans right, but it's the opposite as to which one serves as the backup to the other (as stated by 68FB).
 
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Discussion Starter #19
So I finally was able to test my car. It was 98 / 99-C according to KTEMP.
I was able to stop the Main Fan (that is near the Engine Block (Fan 11 blade - part #11521712110)) with hardly any effort. I used the same steps as last time; rolled up a small magazine and touch the blades.
I'm going to try it again today or in the couple of days, when it gets hotter. I'll try to get the car to about 105-C.
 

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Discussion Starter #20
Today was a much hotter day. I was running A/C full speed so I was able to get my car up to 102-C (KTEMP) and kept it at 100-102 for good 5 min. Temperature gauge started to crawl pass middle and reached the 2nd dot (12:10).
Right away I pulled over. Open the hood and I tried to stop the Main Fan (that is near the Engine Block (Fan 11 blade - part #11521712110)) with a magazine. The fan would NOT stop. I put so much pressure that the blades stated to shred the magazine...............a little bit. So its clearly not the fan clutch. Test took about 5-10 seconds. By the time I got back in the car, the temperature gauge was back to normal (11:58).
So I'm going clean out derbies and do more testing. (I have a feeling by the time I get to it, we maybe in to fall weather by then :) ).

Thanks everyone again for the info and directions.
 
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