I am considering buying a 1998 Cadillac Deville w/ the Northstart v8. The owner stated that the car "overheats" and that there is a coolant leak. Before driving the car I topped off the coolant and drove the car for 20 minutes. The temperature went up to 232 degress max and then came down a little bit. After 20 minutes there was smoke coming from the overflow tank and the coolant began to leak on the passenger side down the radiator. There wasnt excessive smoke from the tail pipes so I dont think it has a blown head gasket. From what I saw there was coolant dripping down from the top of the radiator to the ground on the passenger side and I would estimate a loss of 1/2 gallon. What do I need to replace? Can I rule out a blown head gasket? I am only buying it for $500 and it has 125k.