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help with cooling diagnosis

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help with cooling diagnosis

PostSat Jul 07, 2012 1:27 pm

Basics: 1991 318is (yes, wheezy M42 I4). It shat out the profile gasket a few months back so was (professionally) torn down to the block to have that replaced by the book. The head was not warped or pitted, got bolts, gasket, etc. etc. etc. That work also included a new water pump, fan clutch and thermostat.

When it's a happy little car, the temp gauge runs between a hair under and a hair over the 1/2 mark. Lately, and somewhat randomly, it creeps up to not quite the 3/4 mark. Turning on the heat will bring it back down to the 1/2 mark. The cold coolant level has been the same since the profile gasket work (a little bit below the fill line, but no more than an inch). The top hose does get hot when the car's at operating temperature, but i can still squeeze it (don't remember if i should be able to). And the coolant level rises in the reservoir. No indication of any leaks anywhere.

It has yet to break the 3/4 mark so this isn't really an overheating issue. Any guesses? Am i looking at a stuck thermostat or maybe a gunked up radiator that isn't allowing proper flow through? Or am i just being overly anal.

*Perhaps i should note that i do have the typical, wonky instrument cluster w/o operational odometer and a ground issue that usually means that my speedo and gas gauge rarely work simultaneously, but the temp gauge has never shown signs of being erratic.


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Re: help with cooling diagnosis

PostSat Jul 07, 2012 4:50 pm

I'd guess either blocked-up-with-rust water passages in the block and/or radiator. does the bottom hose get hot too?
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Re: help with cooling diagnosis

PostFri Jul 20, 2012 4:07 pm

Could be the fan temp sensor going bad. I can only guess this is the 195 leg of the sensor not working and the fan coming on full blast at 210* or when you turn on the heater cooling the engine down.


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Re: help with cooling diagnosis

PostWed Aug 15, 2012 1:59 pm

Does this car have an electric fan or use a fan clutch? I replaced EVERYTHING in the cooling system on my M20 powered E30 until I realized the fan clutch was bad. The fan would spin, but could be stopped with a few pieces of rolled up paper. Check the thermostat housing too, I've had two of those fail on BMWs.

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