I'm curious how so many people end up with broken heater cores every spring. When I built mine I positioned hte core/air box so the in/out hoses were at the bottom. When I winterize I pull the block and manifold drains, pull the heater core hoses off the engine and blow out with air, pull the RWP and ciruclating pump hoses and drain from low spots, then attach it all again and run about 5 gals of R V antifreeze through the engine. Once that's done I pull the plugs again, and pull heater core hose and blow air through again. Really doesn't take long and not difficult, only way I can see having problems with heater core is if it was positioned with the in/out ports high, making water difficult to remove.