coolant leak

Please help. My father-in-law has a 95 corsica 2.2L it has a leak which looks like it comes from passanger side about mid range of motor. I changed the water pump thinking it was the problem and coolant was following the frame to mid line of motor. well it is still leaking. The car does not overheat and still have heat inside. It doesn't take long to empty the resevoir and still no overheating. I was thinking frost plug or heater core but need to look the car over again. He did have someone just replace the belt tensioner but I don't think that is related. Any help/ideas I would be thankfull