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40 Deluxe · 01-06-2020, 01:39 PM

Re shut-off valve location: As a general rule, the valve should be in the line coming out of the head (the "hot" hose going to the heater inlet). This prevents possible over pressuring the heater core when the valve is off. If the valve is in the return hose (heater outlet), when the valve is off full water pump pressure is trying to balloon the core since the coolant deadheads and can't circulate. This pressure is in addition to any radiator cap pressure and can be significant at high RPM (especially before the thermostats are fully open).

01-06-2020, 01:39 PM	#5
40 Deluxe Senior Member Join Date: May 2010 Location: now Kuna, Idaho Posts: 3,779	Re: Locating 1937 Ford Heater Hose Re shut-off valve location: As a general rule, the valve should be in the line coming out of the head (the "hot" hose going to the heater inlet). This prevents possible over pressuring the heater core when the valve is off. If the valve is in the return hose (heater outlet), when the valve is off full water pump pressure is trying to balloon the core since the coolant deadheads and can't circulate. This pressure is in addition to any radiator cap pressure and can be significant at high RPM (especially before the thermostats are fully open).