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Does it matter which heater hose goes to the water pump and which goes to the intake manifold? My heater valve is on the upper hose coming out of the core, and I don't know if it matters which way coolant flows through the heater. I have a 351W, 1969 Mach 1.

Thanking everyone for their help...
 

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The manifold hose goes to the lower heater core fitting. The upper hose goes to the water pump. If done the other way, air can be trapped in the heater core and it won't work as well. If it fills from the bottom (from the manifold) as it should, all the air is purged to get 100% flow and heat.
:tup:
David
 

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I agree after all I've read here. I think I'll also put the heater control valve on the bottom hose since I'm in FL and rarely use the heater, hoping the closed valve will keep sudden pressure increases from shocking my old heater core, unless someone knows a reason to keep it on the upper hose?
 

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Between the bottom heater fitting and the manifold. The pump draws water through the heater core, and the valve on the top will mean the heater core is under suction during warmup, and slightly less pressure when hot if the valve is closed, as opposed to pump pressure all the time. Since it is a closed loop, the difference is not great, but everything helps and I agree with your assumption.

David
 

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On the engine I just assembled the water comes out of the intake manifold just behind the thermostat and into the heater core. But either way there will be no air trapped in the heater core regardless if the direction of flow.

They're designed so that air isn't able to be trapped with a free flow of coolant in them, heck man some of the heater cores I put in have the core HIGHER than the feed hose so going either way is of no import to the presence of air due to the design on the flow in the core.
 

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They're designed so that air isn't able to be trapped with a free flow of coolant in them, heck man some of the heater cores I put in have the core HIGHER than the feed hose so going either way is of no import to the presence of air due to the design on the flow in the core.
I tend to agree but in their manual, ford says to bleed the heater core by removing the return hose while running until all air is purged from the heater core then reconnect.
 
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