I have a '77 and recently had the heater control valve replaced. I think hot water is still leaking into the heater core when I have the thermostat on cold. I have adjust the thermostat cable to ensure it was making good contact with the vacuum control. I want to avoid put ting an automatic hand shut-off on the hose. Is there a good quality heater control valve that can keep the hot water out? The heater control valve is on the hose coming out near the engine thermostat, is that correct?