[Tailfin]

Just thought I'd throw in another possibility if this issue isn't long dead.... The thermostat could just be stuck open (which would be cool because that's 6 bucks :coolgleam ). The little valve that opens and closes and allows hot water through to the core could also be stuck closed...or the vacuum hose attached to it could be malfunctioning. If it just needs replacing, it should be an easy find at a salvage yard.