Heat from engine blowing back through firewall

[tabasco85331]

I have a `79 450 SLC that when I`m driving I can feel some engine heat coming from the floor around my feet . Have looked in the engine compartment at the firewall and can`t see any plugs missing . I know I have seen somewhere that this is a common problem . Any ideas ?

[jerryb]

My feet get hot also, but I thought it was from the heater so I wired the valve shut because when you shut off the engine you lose vacuum and the heater valve opens. I still get some heat in the footwell area but can't find where it's comming from.

[tjohn]

Check to see if your heater control valve is shot. The seal can give, and if it does you'll have coolant circulating through the heater core, and giving you hot air, even when the valve is supposed to be closed. You also can have the vacuum element fail, resulting in an always open valve. The valve is on the driver's side (assuming a left hand drive car) of the firewall, it has a coolant hose attached. First make sure the vaccum element pulls the valve shut when the engine is on and the heater is off. If It doesn't the vaccum element is bad. Next drain a gallon or so of coolant, pull the valve, check to see if the interior seal is OK - mine was jammed halfway, keeping the valve open. After replacing my problem went away, and I decided my A/C wasn't so bad after all.