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ray_mcavoy · 01-17-2018, 11:39 PM

I believe that bypass setup was used on all of the pick-up and truck 327's. The version used in pick-up truck applications had a pipe plug in the driver side hole of the adapter and only used one hose connected to a 90 deg fitting on the top of the water pump. The medium duty truck applications (like the one you pictured) used the 2 bypass hoses.

The thermostat should be located on top of the adapter. A bypass setup (such as this) allows some coolant to circulate through the engine in order to prevent localized hot spots from forming before the coolant gets warm enough to open the thermostat and allow full circulation.

The small block Chevy water pumps & blocks do have a built-in bypass passage located on the passenger side (just below the lower water pump mounting bolt). I'm not sure if that bypass was blocked off in these truck applications so they used the external bypass hose(s) instead. Or if it was left open allowing flow through both passageways. I think some Corvette 327's used a similar (but not identical) external bypass hose connecting to the top of the water pump.

01-17-2018, 11:39 PM	#2
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,354	Re: Thermostat housing bypass 1966 I believe that bypass setup was used on all of the pick-up and truck 327's. The version used in pick-up truck applications had a pipe plug in the driver side hole of the adapter and only used one hose connected to a 90 deg fitting on the top of the water pump. The medium duty truck applications (like the one you pictured) used the 2 bypass hoses. The thermostat should be located on top of the adapter. A bypass setup (such as this) allows some coolant to circulate through the engine in order to prevent localized hot spots from forming before the coolant gets warm enough to open the thermostat and allow full circulation. The small block Chevy water pumps & blocks do have a built-in bypass passage located on the passenger side (just below the lower water pump mounting bolt). I'm not sure if that bypass was blocked off in these truck applications so they used the external bypass hose(s) instead. Or if it was left open allowing flow through both passageways. I think some Corvette 327's used a similar (but not identical) external bypass hose connecting to the top of the water pump.