I have a 1990 audi 80 4 cylinder automatic with 130,000 miles, that keeps losing antifreeze and can't find the leak if any . The heater blows cold air and yet the car doesn't over heat at all . Every couple of days I have to add a small amount of coolant to the resevoir so the lite will go off . I smell antifreeze when driving and when sitting at a light or in traffic in starts to miss. When I take off ,there is a cloud of smoke or steam , not sure which. I have no water in the oil , but do have an oily sludge in my resevoir . Is this a head gasket problem or is there something else that could cause this?