I usually commute 30 miles every day in my 87 740 Turbo. My wife drove it recently and had a cold ride; no heat. When I checked the coolant level it was low. I changed the thermostat, then topped off the coolant. Next day, drove to work, car sat all day (it's been fairly cold here; highs around 10-12F). Before I left work for home I checked the coolant level; had to top it off a little, figuring the drive down moved out any air introduced with thermo change. Next morning, coolant OK. Drove home, checked later in the night, coolant OK. Checked this morning before leaving for work, it was down again. Tonight after returning home, checked level after engine had cooled (it's really cold tonight) and it's down, checked again later and down some more.

So, I'm puzzled when and where am I losing coolant? Any ideas? I've read the FAQ, and there are many possibilities, so asking if anyone recognizes these observations.

Thanks for any and all help.