'67 H20 PUMP BYPASS( HOSE) PURPOSE?

[Rob A.]

What exactly is the purpose of the H20 pump bypass(hose)?

[Joe L.]

Re: '67 H20 PUMP BYPASS( HOSE) PURPOSE?

Rob-----

1) It provides a bypass around the thermostat in case the thermostat should stick shut. This provides some cooling and prevents a catastrophic overheat situation;

2) Supposedly, it helps the heater function sooner (provide heat to the car)than it would without the bypass. I don't see how this can be the case, but I've heard that.

[Rob A.]

Re: '67 H20 PUMP BYPASS( HOSE) PURPOSE?

Thanks Joe...

[Clem Z.]

Re: '67 H20 PUMP BYPASS( HOSE) PURPOSE?

it allows water to circulate thru the engine when the thermostat is closed. the small block has a passage drilled in the water pump leg where it bolts to the block so it does not need the external hose.when we used restrictors instead of thermostats in big block race engines we blocked off the bypass because it cause too much water to bypass the rad and just recirculate back thru the block. i ofter wondered if owners who have overheating problems with their big block corvette would block this bypass would it help.

[Duke W.]

Re: '67 H20 PUMP BYPASS( HOSE) PURPOSE?

There are actually up to three bypass circuits - the heater core circuit, the "internal" bypass described by Clem, and the external bypass between the top of the pump and inlet manifold.

When the thermostat is closed the greater the bypass flow area, the greater the rate of coolant circulation. High coolant circulation when the themostat is closed is considered good to promote quick and even warm up.

The external bypass was only installed on SHP/FI 327s (not sure about 283s), but was eliminated in the last year or two of the L-79 as I recall.

So an early 327 could have as few as one or as many as three bypasses. The C-48 heater delete option eliminated the heater circuit as a bypass, and if you ordered C-48 on a medium performance 327 you only got the internal bypass.

I can't make much sense out of all this. I guess Chevrolet decided that the external bypass was not necessary and eliminated it, but I think it would be a good idea if you have a heater delete car.

No bypass or too small a bypass will slow warmup and could possibly cause water pump impeller caviation at medium to high revs when the water being pumped has no place to go.

Duke