My Xplorer 400 won't run due to coolant mixing in the cylinder. I removed head and jug to pressure check on bench - no leaks and no visible cracks. Head gasket looked fine. I pressurized the cooling system and looked into the crankcase - no leaks. Am I crazy? Where is this coolant coming from? Any common issues to help me guess??? Do some leaks on these only occur when hot? Can the water pump leak into the chamber? I'm drawing a blank on this one.