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Re: Cooloing System Inquiry (archive)

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Posted by jej on December 09, 2001 at 18:32:14:

In Reply to: Re: Cooloing System Inquiry posted by John A on December 09, 2001 at 00:00:06:

John, thanks for your suggestions. Since I can see the fluid discharging through the overflow tube, (the uppermost one pointing towards the front of the car on the coolant reservour tank), it would appear that a blown head gasket is unlikely. Further, I am not seeing any coolant either on the coolant tank or underneath it.

What is baffling, is that the thermostat would need to be sticking in the closed position during the warm weather conditions, but then in the open position during the cold weather conditions. Perhaps it is a function of the pressure build up?

My '88 M3 has a rather strange cooloing system problem. I warm weather (60 F), I usually run the AC fan to keep the engine cool, i.e. I have a leakin the refrigerant system, such that the fan will turn on, but the compressor does not engage. My temperature guage will stay just below the mid point.

In cold weather (30 F), it is hard to get much heat and the temperature guage doesn't register at all or stays in the blue area. This is with the AC fan turned off. The engine fan seems to always be working.

Recently, in cold weather, coolant is being discharged through the reservour overflow tube that runs into the right side frame. I have replaced the reservour cap, but the problem persists to the point that the coolant warning light comes on, most likely the sensor indicating the coolant level in the reservour.

Before replacing the thermostat, I would appreciate any other recommendations or testing procedures. Thanks in advance, jon

It certainly SOUNDS like the thermostat is stuck. Not getting enough heat when it`s cold is a good indication of that.
In my case, the loss of coolant turned out to be simple; the cap wasn`t sealing on the old tank. Looking closely, I realized the plastic rim on the tank where the cap goes on was distorted, preventing it from compressing the spring enough to seal. I squeezed the tabs on the old cap the same amount as the distortion and it sealed. I then got a new expansion tank and cap...no more loss of coolant.
Another (more expensive) explanation for the coolant loss is a blown head gasket, where combustion gases are overpressurizing the cooling system. An exhaust gas analyzer can be used to test for combustion gases in the expansion tank.




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