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The attached picture shows the water pump that was on my early 63 NOM dconvertible (restoring as driver). It has no GM markings, and I assume it is aftermarket. I bought a rebuilt 3782608 which does not have the additional threaded outlet on top. I read a thread in the archives (Jan 05)on 63 water pumps and I believe that the additional outlet was referred to as a bypass. Can someone explain the bypass function to me ?
When the themostat is closed the water has to go somewhere from the pump or it will cavitate at relative low RPM.
The bypass allows engine out coolant back into the pump inlet chamber where pumped back into the block. This prevents cavitation AND facilitates quick and even warm up.
Corvette engines have up to three bypass circuits. The first is the "internal" bypass" - the third hole is the RH pump leg. Early SHP/FI engines have the "external bypass" from the inlet manifold to the top of the pump housilng, but this was eliminated on later SHP engines. The third bypass is the heater core circuit, but it would not exist on C-48 cars.
Once the thermostat opens the bypass circuits are still open, but since the radiator circuit has much greater flow area, most of the coolant will flow to the radiator,
Some engines have thermostat designs that simultaneously block off the bypass circuit(s) as the circuit to the radiator is opened.
You did not say what engine horsepower your '63 is equipped with. If it is a 250 or 300 hp then the 3782608 water pump without the bypass is the correct one. If it is a 340 or 360 FI then you would need a waterpump with the bypass. I know you said that the engine is NOM but does the intake manifold on your engine have provisions for the bypass hose to the water pump? If it does not, then you don't need the water pump with the bypass. You can buy a remanufactured GM 3782608 water pump from NAPA for around $18.00 with core charge. I recently purchased one of these for my '64 327/300 hp Corvette as a spare to take with me only the NCRS Road Tour this summer.
As far as I know,all SB pumps/blocks have the internal bypass, so even if the engine has no external bypass and C-48, there is still the internal bypass.
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