Engine got overheated due to a ruptured heater hose on back of engine. It continued to run for some time while more water was attempted to be added. Now the engine starts ok and runs ok, but after it gets warmed up it will blow a cloud of steam out the exhaust, which goes away at higher speeds. This week I intend to change the head gasket, but, the possibility occurred to me that there may be a cracked head or block. What should I do? Can I do it myself, or do I have to send it out?