II have an 1972 Oldsmobile Cutlass V8. I over heated due to a rusted Heater Control Valve that is Vacummn controlled. Due to the summer heat this project was spread over a couple of months. During the replacement of the Heater Control Valve I removed a couple of Vacummn lines, one on purpose and accidental disconnected a second line…. One went to the Heater Control Valve and the other apparently to the transmission hard line coming up behind the engine.. one is a short line and the second line a larger line teeing into a line from the Vacummn can…. I originally thought the short one connected the transmission and the HCV but that makes no sense. However if I connect the short line to the HCV I can’t find a male port to plug it into? I’m obviously missing something.

 

The heater control valve malfunction will not cause the engine to overheat. The vacuum modulator line to the transmission needs full manifold vacuum.

 

The HCV vacuum hose comes through the firewall from the dash controls - it does not connect to a male vacuum port on the intake manifold. Look around between the rear of the engine and the firewall as the loose end may have dropped into that area.

 

I may have miss spoke about over heat. As I pulled into the driveway steam was coming out of under the hood. When I opened the hood the steam was being released from the heater hose connection to the HCV. When I took it apart the valve male connection was rusted half away allowing water pressure to escape. Giving an appearance of over heating. However the antifreeze fluid I flushed out looked new and not a bit over heated. So your probably correct.

 

Thank you, That is great information. I will be looking for it.