In my experiences whenever the head gasket blew the oil and water always mixed. My friend has a 95 5.0 with 100k plus miles and the dealer is saying it has a blown head gasket, but he says the oil and water isn't mixing. Is this possible? He says whenever he turns on the heater he smells antifreeze. Sounds like the heater core to me, but the dealer told him that it's a blown head gasket.