E36 M3 Overheating issues at idle

[tlundberg]

My 1998 E36 M3 will slowly overheat sometimes at idle. When I rev the engine a bit, it will cause it to go back down. I used to have a small leak, which is what I thought was causing it but I fixed the leak, and its continuing. Yesterday, it started to creep up at idle, even with plenty of coolant in it. I refilled the coolant, and properly bled it ( may have been problem, since it was first time it was filled since leak was fixed and I wasnt the one to fill/bleed) and its been fine since and has no low coolant warning on OBC. To the best of my knowledge, It is not a problem with the head gasket, we did a chemical test a few weeks ago and it did fine. Also, (supposedly) everything in the cooling system was overhauled (except hoses which were causing leak) before I bought it, like the thermostat, water pump, etc... There are now no leaks coming from the car, but it still crept up yesterday. Both of my fans up front work, also. My AC blows cold, but not very hard at all. Thought Id throw that in there just in case.

Note- It will creep back down when revving engine between 1 1/2 - 3 rpm, and goes back down as soon as i start driving.

What could be the problem? Was it not bled properly (which should be now, no low coolant on OBC)? Is something wrong w water pump, thermo? Any help is appreciated. Thanks guys!!

[scooper]

pressure test the system and look for more leaks. Bleed it and bleed it some more. Where was the leak?

[mitch500]

That's typically a faulty thermostat when your heat goes up at a light then back down once you start driving.


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[sharadn]

Check your fan clutch

[Eric93se]

Sounds like water pump failure, possible to have a faulty new one.

Do not let your car come anywhere near overheating!

[CGumina]

I'm going to vote for a failing waterpump as well. Not pulling enough volume at idle = not enough circulation, slowly cooking the motor.

Has the water pump ever been done?

[tsmith25]

Check your fan clutch

Usually overheating while not moving is related to the fan. Inadequate air flowing through the radiator means that the coolant is not exchanging enough heat before being pumped back into the engine.

your fan clutch is probably not grabbing well enough to get enough flow at idle. then when you increase the revs, that is enough to cool it back off, for now.

Get your engine up to temp, then turn it off. Then try to spin the fan by hand. If it is easy to do, then your fan clutch is worn out. It should be easy to spin the fan (with the engine off) when the engine is cold, but much stiffer when the engine is hot.

[DocWyte]

Check your fan, fan clutch and the auxiliary pusher fan.

[jayjaya29]

System isn't fully bled yet.

[tlundberg]

Thanks guys. Like I said, supposedly everything like the water pump and thermo was replaced the day i bought the car, He had receipts, but i guess I have no way of knowing for sure. Ever since I bled the system the other day, it seems okay. No overheating, or anything. Even no check coolant level on OBC, which is usually on everytime I start and turn off car (except after I JUST filled it). I will do the tests you guys suggest, and also keep an eye on it, but for now it seems bleeding it correctly has done it good. i appreciate it guys!

[tlundberg]

I spun it at temp. It has resistance, but im not sure how easy or hard is considered time to replace. It cant spin all the way around w one push. I have seen peoplle talk about deletingthe fan in all, is that recommended? Would that increase likelihood of other parts failing, or make engine sit a little hotter?

[DocWyte]

I wouldn't delete it. Either do an electric fan conversion or get a new fan clutch.

I've got 2 spares, both good if you want. One is basically brand new, the other used but good

[LockDots]

I spun it at temp. It has resistance, but im not sure how easy or hard is considered time to replace. It cant spin all the way around w one push. I have seen peoplle talk about deletingthe fan in all, is that recommended? Would that increase likelihood of other parts failing, or make engine sit a little hotter?

Just because there's resistance doesn't mean it's the right amount of resistance. Overheating at idle is typically the fan clutch going (if it hasn't fully died yet). Either get a new clutch or switch to an electric puller. The electrical puller will be more "customizeable" but will also require more work than swapping a clutch and blades.

[tlundberg]

Hey y'all, so after filling it and bleeding it last ( right before i made post) it has only crept up on me once, which is why i made the post. Its been very hot here the last few days, and ive even been using my ac, and the temp has been fine. Knock on wood but I hope there was just an air bubble or two. I always stare at the temp gauge looking for it to creep up, but this last week, even w hot weather and using ac, it seems to be fine! Would you guys recommend unscrewing the bleed screw again when at operating temp to maybe get any possible air pockets out? Anything else I could do to make sure? Thanks guys!

[shogun]

If only overheating at idle, it is the fan clutch. New fan clutches are cheap nowadays and easy to replace.
Here is a good write up by MWRENCH, once written for the E31, but also valid for the M3:
Fan Clutch test
First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed. When cruising down the road at freeway speeds, with outside temperature less then desert conditions, the fan should be merely be idling along, turning just fast enough to add a little air flow when needed, in this way the fan noise and drag on the engine is greatly reduced. When reducing speed, the fan clutch will sense higher temperatures thru the radiator and “clutch up” thereby increasing the fan speed to help maintain constant engine temperature. It may in fact, cycle as the temperature of the air thru the radiator changes depending on airflow. If the fan clutch operation is normal, first starting the car, the fan clutch should “clutch up” and an increase in noise and airflow should be obvious. After about 60-90 seconds, the fan will un-clutch and the noise and airflow will drop. The fan will continue to turn but at a much reduced speed. As the engine warms and the thermostat opens to regulate the temperature, the air thru the radiator gets hotter and the clutch will sense this, thereby increasing the speed of the fan to maintain a normal operating temperature.
First signs of trouble:
A normal temperature indication at freeway speeds and an increasing temperature as the vehicle slows is one of the first indications of trouble. Many other things may give this indication but if the temperature seems to be stable at speeds but climbs in traffic or while stopped, this is a good indication that the fan clutch isn’t working correctly. As the temperature continues to climb, the auxiliary electric fan should start but may not provide enough air to keep the engine from overheating.
Another sign of trouble is if the fan noise is high and never decreases after starting, and is there anytime the engine RPM is higher then idle, this means that the fan clutch is “frozen” and is not releasing. Although this will not result in immediately serious trouble, it will load the engine continually and gas MPG will be reduced. Load on the fan belt(s) will be higher and shorten the life of that component also.
Fan modifications:
It has been suggested that other models of BMW fans can be substituted to reduce the noise and load of the fan. This is NOT recommended! If the fan clutch is working properly, there should be no need to replace with a lesser fan. The noise and load of the fan should only be there when it is “clutched up” and the fan speed needed to keep that big V-12 cool. BMW designed it this way and it is never a good idea to alter the cooling system and in particular where alloy engines would be effected.
Testing the fan clutch:
If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good indication, if it does not increase speed/noise, clutch is bad and needs to be replaced.
(Remember, this must be tested after the car has been off for and extended period, over night etc.)
2. Leave engine running and note if the fan starts to slow down after 2-5 minutes, speed/noise should diminish and even raising the RPM, the fan should not make as much noise as when first starting, if it does slow, this is the second good indication. If
speed/noise does not decrease, clutch may be “frozen” and should be replaced.
3. Leave the engine idle and watch the temperature indicator. When normal operating temperature has been reached, some increase in fan speed/noise should be noted, in particular when the RPM is increased. If temperature is fairly stable and the fan
noise/speed increases or cycles, third good indication. If temperature indication continues to increase, with no increase in fan noise/speed, clutch is defective and should be replaced.
4. After the engine is at normal operating temperature or above, is the only time that the “rolled up newspaper” test that many people talk about should be performed! Take some newspaper and roll it up into a long narrow tube. Be carefull, keep hands and fingers away from the fan while performing this test! With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub. Push the
rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.
Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test. Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches “redline”.