Hello Everyone I have a 1997 Chevy Express LS 1500 conversion van with a Vortec 5.7 motor. About 2 week ago I was driving the van and it started to overheat , after getting it home I noticed I had oil in the radiator overflow and I started to hear a knocking in the motor on the passenger side ... but the knocking only happen when the RPM get to about 2000 rpms.... No water on the oil dip stick, but it was signs of water in the oil filter .. I was told a head gasket but the van lost NO power nor did smoke come out of the tail pipe , and I was also told it could be a manifold gasket. PLEASE HELP !!!!!!!!!!