I've had a perplexing coolant loss the last year or so. It seems to be correlated to heating usage. I'm wondering if its a minor leak at the heater core? We are talking about 1/8~1/4 gallon loss over 8 months/20,000 miles. About 2-3" on the overflow reservoir. Since it's been warm for the last month or so, I topped the coolant off and I haven't lost a drop since I stopped heating.

I never smell coolant inside the interior. Obviously no wet spots on the carpets or anything. I do sometimes hear a "gurgle" from the heater core when I start the car with heating turned on. Not sure if that's normal or not. No signs of coolant leaks anywhere in the engine compartment or by the battery. Some white crusty residue on one of the windshield washer heating lines. Is the washer fluid constantly heated? Or only when the heat is on? Thanks....

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1991 300E - 212K and rising fast...

Its constantly heated in the reservoir, crazy huh. Glad it has a cap or it would all evaporate. You could pull your wiper assembly, open the vent box and clean the condensor and look at the core to see if the is a bunch of antifreeze there. But how much your talking about could have been stop and go on a hot day and popped the cap and let some out.

Unless I'm mistaken, I believe the washer system is heated continuously. I had that same gurgling noise from inside the car. From what I've read it is trapped air inside the heater core that causes the noise. I had a few leaks coming from a heater hose and expansion tank line.

They were very small leaks but nonetheless I lost a bit of coolant over 6 months. The white residue left as the coolant dried was the clue. I tightened up all the connections and then took off the expansion tank cap and ran the engine at 2000 rpm for 5 minutes on a slight incline with the heat on max. This finally stopped that annoying gurgling sound whenever I ran the heat. It was simply air trapped in the coolant system that needed to be bled out. I would pressure test for leaks and then see if you can identify any leaks particularly around heater hoses.

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1989 300CE

Hopefully not the head gasket.

Any over heat problem?

Head gasket has been done already at 120k. No loss of coolant when I'm not using heating. I am loosing very small amounts of coolant over the course of the winter only.

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...