'97 Venture Cracked Head?

My girlfriend has a '97 Venture van that was bought with a busted head gasket. My mechanic supposedly fixed it but I'm not sure. After having it for 6 months, a fan rubbed a big hole in the radiator while I was driving it. This caused it to overheat(peg out) before I could stop it at a gas station. The next day I came back with a gallon of water and stopped every mile or to allow it to cool. After getting the radiator fixed today, another mechanic tells me that I have either a busted head gasket or a cracked head. He explained how they knew(some test with a clear cylinder of blue liquid that turns yellow). The problem I have believing this is that the oil is still dark. Could the crack be so small that it hasn't changed the color of the oil? Another problem is that I DO have white smoke coming out of the tailpipe when I first start the van but after 5 minutes, there's no more smoke. Did my mechanic screw me on this?