My 87 is drinking coolant. sipping maybe is a better word.

i have spent a few hours searching a reading the forum. my car has no apparent symptoms of a cracked cylinder head. there is no oil contamination in the expansion tank, the car has never come close to overheating in the 2+ years i have owned it. it doesn't seem to have residual pressure in the upper coolant hose, however it is not clear to me what a "hard" hose should feel like, exactly. there is fluid in the upper coolant hose when the car is cold, but when you squeeze the hose the fluid just moves around. it doesn't feel like the hose is pressurized.

the car does not emit any white smoke. there are no odd smells or anything else i can identify as significant to the loss of coolant. i replaced the water pump last summer and there were very small traces of leakage (stains on the oil sump) from the pump, but those traces are now gone and there was never even a drop of coolant on the ground. the only sign is that the coolant disappears. it seems to be accelerating - i think it used to be maybe 2-3 months and i would need to top up the tank. recently i topped up the expansion tank and it was nearly empty in 10 days. the car is well maintained, MB coolant, and has been a perfect trouble-free vehicle for about 2 years. it still runs perfectly, but the vanishing coolant is worrisome. i did a cooling system pressure test in the spring and it held pressure fine.

the only thing i can think of is that the heater core may have a slight leak. if the climate control is left on when you shut off the car, then you start the car the next day or a few hours later, the windshield gets fogged up and the air smells a bit funky. this clears up quickly. the car has done this pretty much since we've owned it so i haven't been too concerned. but it makes me think there is a leak in the core because the moisture has to be coming from somewhere.

anyhow, thanks to anyone for some ideas on what to do next. i am a mechanic but the vehicles i work on have no radiators! i am slightly lost when it comes to watercooled cars...

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punkinfair