'66 Mustang GT with 4 barrel 289. Passenger side has constant flow of hot air coming from somewhere, car runs hot whenever in stop and go traffic, sputters. Was vapor locking but plate fixed. help!
Most likely the seals are shot in the heat control doors allowing air to get through the blend doors and into the heater core, so you can either pull the heater box assembly out and redo all the door seals or just put a hot water shut off valve in the supply heater hose, that would be th one coming out of the intake manifold to the heater core. Stop and go was and still is a problem for these Mustangs, that is why so many have went with electric cooling fans, some have wired then up with an over ride switch so they can turn them on at anytime or switch it back to automatic.
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