The white smoke comes and goes. Do not see any yuk in the overflow but it is rather low so cant see much. Does not seem to be an inordinate pressure build up in the overflow tank. The car is chugging and idling a bit rough. Will a compression test reveal coolant leakage into the cylinders. I wish I could get the check engine light to go off as I cannot get the OBD system to work. Incidentally, what are those green rectangular lights on the dash just above the steering column light.