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BMW E36 M52 Intermittent Heat & Running Hot

April 15, 2010

This answer is applicable for many BMWs in addition to the one listed below.

car year: 1997
car model: 328i Convertible
There is something unusual going on in my cooling system. I am not sure what is wrong. Symptoms: – Heater/Defroster only gets hot intermittently even when the engine is up to normal temperature (engine does not take a prolonged period of time to get up to temperature). After normal or prolonged driving, then idle, the engine temperature continues to drift up and gets very high (sometimes into the red, sometimes not) before cooling back down. Not sure if these two items are related. Just interested if there is a “common” problem before I start trial and error to find the problem. Thanks

From your initial description of the symptoms, We could be dealing with any of the following issues:

* Faulty heater control valve (controls the flow of the hot engine coolant to the heater core).

* Faulty climate control panel (improper control of the heater valve).

* Thermostat

* Faulty engine fan clutch and/or electric auxiliary fan system.

* Low coolant level.

* Faulty BMW original water pump (broken plastic impeller).

For a start, have you visually verified that the cooling system is actually full …. regardless of what the coolant level sensor is telling you? If it is, go on to the next step. if not, add coolant as needed and see if the symptoms change.

Let’s look at the intermittent heat issue. Locate the heater control valve. On your E36 chassis (3 series 92-98), the valve is located on the firewall, just inboard and below the large round brake booster housing. Unplug the electrical harness plug from the valve. This will make the valve go to full open (hot), if it is working properly. You should now have full heat on both sides of the car (regardless of the climate control temperature setting). If you do not, the valve is likely faulty. If you do have the appropriate full heat, all the time, then the valve is likely OK and we will diagnose in other areas.

Click below for Heater Control Valve:

The heater control valve will not cause the engine to get hot. So, we still have an apparent issue in this area. When idling, and the temp goes high, does it always come back to normal and then does it stay there and not rise back up …. when idling, on a hot day? Additionally, it seems that you noted that the temp never goes above normal except when you come to an idle after running on the highway. Is this correct?

  1. Mark permalink

    Trying to unplug the heater valve connector, with zero success. Anyone know the Bavarian Secret involved here?

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