Coolant hose from pump to intake manifold

[Joseph E.]

What is the purpose of the hose which runs from the top of the water pump to the intake manifold? I was talking with a few friends this weekend and one had told me he restricted coolant movement through this line by blocking the passage inside the hose. He tells me that his car seems to run cooler after having accomplished this. The blocked hose was left in its stock position to maintain the proper appearance of the engine. His car has is an L72 setup in a '66 coupe. Does anyone have an opinion as to whether or not this is safe to do and would it result in a coolant temperature drop? Thanks.

Joe

#45420

[Duke W.]

Re: Coolant hose from pump to intake manifold

That's the external bypass hose, which was used on some SHP/FI engines both SB and BB. Theoretically by blocking it more coolant will flow to the radiator when the thermostat is open, but this does not necessarily solve "problems" as further discussed below. The heater circuit is also a bypass, and I think the BB has an internal bypass built into the coolant pump like the SB.

When the thermostat is closed coolant is recirculated back into the engine through the one or more bypass circuits. If no bypass is present, coolant will not flow in the system, the pump will cavitate, and engine warmup will be uneven.

The larger the bypass area the better the coolant will circulate during warmup to promote quick and even heating, but it also allows more coolant to recirculate when the thermostat is full open. This doesn't mean the engine will run hotter because of less coolant flow to the radiator because the lower the coolant flow rate through the radiator, the more time it has to shed its heat. Heat transfer is never a simple problem because there are four independent variables - coolant and air temperature along with their respective flow rates.

All the above said: The reason your buddy's L-72 runs hot is because it has ported vacuum advance. Converting it to full time will eliminate the problem without diddling with the bypass.

This issue has been discussed numerous times including in the last week. Do some archive browing to find out the story.

Duke

[Joe L.]

Re: Coolant hose from pump to intake manifold

Duke and Joe-----

There's no internal bypass on a big block. Without the external bypass, there is no bypass. I would not run a big block without the external bypass properly functioning. Besides, there is no advantage I can see to eliminating the bypass.

[Duke W.]

Re: Coolant hose from pump to intake manifold

I'm learning something new about big blocks everyday!

If the external bypass is blocked the heater core circuit would then be the only bypass, but the best course of action is to leave the coolant pump external bypass intact and convert the vacuum advance to full time.

This has solved hot running/overheating for EVERYONE who has done the conversion. If converting to full time vacuum advance doesn't reduce low speed hot running/overheating then there is something else wrong with the cooling system, like excess radiator deposit buildup or the fan clutch is no operating properly.

Duke

[Clem Z.]

after owning new BBC corvettes in 65 and 66

and i had no problem with overheating so i think something has changed since then. maybe it is global warming !!!!!

[Allan J. Wicklund]

Re: Coolant hose from pump to intake manifold

It often surprises me that "Shade Tree" mechanics sometimes create a problem in their attempts to solve a problem. Design engineers get it right 99.99% of the time so why fight the odds. A good mechanic is a good diagnostic Technician and too many people fail in this endeavor. Al W.