BMW Overheats When Idling

BMW
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NB0474
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  • 2 POSTS
I need a good problem solver. I have a pretty good idea what might be wrong with my car, but I'd certainly like to hear from bmw community.

Signs:

Car overheates when idle(maybe after 15 minutes of idle).
Never overheates when driving or on stop signs.
When it starts to overheat I turn on heating and it cools down.
When it starts to overheat I turn on air conditioning and it cools down.
When it starts to overheat I press on the accelerator and keep it at 2500 rpm and usually cools down (not all the time, but most of the time).
No coolant leaking or coolant loss.
I didnt' do the compresion test but I bought that Napa combustion test kit that checks if there are exaust gases in coolant and it was clear (I did it few times).
I tried to stop fan with paper when it was very hot and I was able to do it without too much pressure. When I try to turn it when engine is cold there is some force stoping it but not a strong one, so it doesnt move freely on shaft, just a few rotations and then it stops.
My auxiliary fan works (I tested it with 12DC) but never turns on (even with AC on). I still think it should turn on when engine overheats (I wish I could get to that fuse #75 to check if it was blown).

My final diagnosis is Fan Clutch.
Let me hear your opinions??
Feb 27, 2006 at 6:47 AM
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2CARPRO JACK
  • ✓Experienced Mechanic
  • 11,533 POSTS
sounds good
Feb 28, 2006 at 9:27 AM
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BAMADAVE
  • MEMBER
  • 8 POSTS
The electric fan should come on period when the ac is on or the engine runs hot. Replace the fan sensor. Now your going to ask where it is. If your mechanically knowlegable, buy a manual to learn your engine. If you refuse to buy a manual, take it to a shop. You will end up burning up your engine trying to keep it cool.
Mar 29, 2006 at 10:57 PM

Suggested Repair

Replace the electric fan temperature sensor so the auxiliary fan comes on with the air conditioning or when the engine runs hot. One reply also agreed the mechanical fan clutch diagnosis sounded reasonable. If you are not comfortable locating the sensor, use a service manual or have a shop diagnose it before continued overheating damages the engine.

Conversation Summary

A BMW owner reported overheating only at idle, with no coolant loss and a negative exhaust-gas-in-coolant test. Heat, air conditioning, or raising engine speed usually brought the temperature down. The mechanical fan could be stopped easily when hot, and the auxiliary fan worked on 12 volts but never came on, even with the air conditioning. The owner suspected the fan clutch. One reply agreed that sounded reasonable. Another said the electric fan should run whenever the air conditioning is on or the engine is hot and recommended replacing the fan sensor, or using a manual or a shop to avoid engine damage.

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