My daughter's C70 has been slowly loosing coolant. The coolant tank has some staining or something that looks wrong, and I suspect some problem of somekind before we bought the car.

After about 8 months I needed to add 1/4 to 1/3 gallon of distilled water (no Volvo blue coolant on hand). I thought that there was a very small crack in the top of the coolant tank, but was not sure, it was so very tiny. Ask for details if you want.

However, after topping off again, only a few ounces, it has not lost any coolant, and there seem to be no leaks, and the level of coolant is staying where it should after about 24 miles testing.

I do have a new coolant tank (genuine Volvo), and was looking for where the coolant or radiator drain petcock was, and it looked like there was a bit of water down in the frame, just below the lower radiator hose on the passenger side. However, the coolant level in the tank was exactly where it should have been. It had rained the night before, very heavily, and I can't get my hand down there to feel the liquid and see if it is coolant or rain.

Questions: Where is the coolant drain on the C70? What do you recommend I do? Continue watching carefully, replace the tank and inspect the hoses? Any other ideas?
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1955 Human, Scott; 1991 745 Turbo, Thunderbolt; 1994 940, Straxx; 2008 C70, Draco