On my 1990 Caprice Wagon (Olds 307 Vin Y), there is a vacuum actuated hot water valve on the rear of the manifold. The heater core outlet hose runs to this water valve, which screws into the manifold.

When the dashboard temperature selector is set to hot, there is zero vacuum to the valve. If the temperature selector is moved to cold, vacuum is applied to the valve.

Problem: When vacuum is applied to the valve it begins leaking coolant. If I remove the vacuum hose, the leak stops. A/C still works fine. Heater still seems work OK.

Question: Is there anything wrong with leaving this vacuum hose off and fooling the valve into thinking the heater is on whe it isn't? Is this reducing or increasing coolant flow to the block? Does this make the car run hotter?

Not sure exactly how this valve works, so appreciate any thoughts on this.

Thanks a lot.

i always remove the valve completely and connect the hose to the heater core directly, i do this to all my cars i get, just did it to the 84 the other day, and the 78 when i got it not too long ago


never a problem anymore after that

good luck

Thanks for that. I wasn't sure if it was a normally open valve or normally closed.

But since its normally open, I'll just get rid of it all together. A/C and heater both work fine... begs the question why would GM even put it there.

Thanks.