Question about 1998 BMW M3

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Over Heating Hi all - for the 14years I've been doing mechanical work on cars this flipping BMW 1998 316i Auto is getting me frustrated. We purchased the car not long ago. It was obvious that the previous owner hadn't serviced it often. Anyway at first the heater wasn't working - only a minor issue I thought, so carried on with oil & filter change & new Bosch spark plugs. Them I thought I would sort the heater problem, so flushed radiator, engine & heater core also reverse flush. Replaced the thermostat & top rad pipe (a little soft), flushed until completely clear & running freely, replaced distilled water & coolant(only the best), still no heater? However since doing all the above the car is now overheating, before you ask yes I did bleed her for@@##**& hours. Checked for leaks nothing, did the dye test for water in the wrong places all ok there. No signs of water on the floor area inside. Checked all pipes for cracks etc nothing. When the car is in the red zone the refill tank sounds as though there's a loose ball bearing inside (just giving an example) Almost ready to buy a car cover & forget she's there! Any thoughts would be appreciated. Will be checking the fans tomorrow if it doesn't rain as it's winter here now - cold & WET. Many thanks viewers.

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Heater core and radiator are separate issues. But, both may have the same problem. The best non-commercial way I have found to remove internal obstructions from either is to use a household calcium and rust remover (like CLR)...On heater cores, remove both hoses and fill the core with product, then let it stand for a couple of hours. then drain and backflush.
On engine radiator, remove it, plug the lower hose connection and do the same...fill with product, let stand then backflush, then turn radiator upside down & repeat in opposite direction. The reason standard water flush often does not work is that water simply goes around the plugged area and does not remove anything except for minor debris which sometimes can actually plug other passageways and make the condition worse.
Back to the heater. It's possible that a blend door is not operating and therefore not allowing hot air to enter the heater box...check this as well.
Definitely make sure that fan is coming on and that the thermostat is actually working (I don't trust anything new just because it's new) Also check sensor & relay for fan.
Likely information "overload" but I hope something here helps!

Posted on May 15, 2009

  • marty007 Mar 18, 2011

    hi there, i have had dealings with bmw 97/98, a common cause is head gasket and if so the head could be warped...the nickname is chocolate heads...they warp very quickly,from good luck.



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