EFE(Heat Riser) valve
- Thread starter 84 delta 88
- Start date
- Status
It should be in the normally open position. The way it works is, the valve is spring/counterweight loaded to be normally open. When the engine starts and produces vacuum, a Thermal Vacuum Switch senses it is cold and supplies vacuum to close the valve, forcing hot exhaust gas to pass through the intake manifold under the carb, getting it hot faster to aid fuel atomization. When the TVS senses coolant at about 100º it cuts off the vacuum and vents the EFE valve to atmosphere, allowing it to open. The EFE works in conjunction with the THERMAC heated air cleaner which heats intake air to around 100º also. This is important because the stock carb is jetted for use with hot intake air. Thus, a capped EFE vacuum line and missing THERMAC foil exhaust manifold tube would result in slow cold carb warmup and rough running which would be very noticeable in winter, not so much in summer.
Last edited:
when i pull the cam that is connected to the little door inside the heat riser it has tension on it so when i pull on it and i feel tension is that opening it or colseing it
It should be normally open and pulling on it should close it. Think about it. If a vacuum hose broke or TVS failed, the default position would need to be open. If it failed in the closed position you would have all the exhaust on one side traveling under the carb and boiling the fuel. The old style "heat riser" valves used a counter weight and bi-metal coil. They failed all the time in the closed position, causing just that.
Anytime you buy an old car with hear risers removing them should be the first modification. I have pulled some off that were gutted and had the shaft holes plugged. Those and the original style catalytic converters were the only thing that ever frustrated me on these cars. I'm not against catalytic converters, but those originals really didn't play well with carbs.
The ones I pulled off of the 3.8 that used to be in my car were like new. I believe the last owner may have replaced them.
It doesn't hurt anything when it's working right. In fact you never even know it's there until it sticks open or shut, shut being worst. But if you are using the car for a daily driver and it gets cold by you, well, shivering in the car until it finally warms up and runs smooth gets old.
I've never had a problem On the cars I remove them from or the ones that never even used them. It is a foolish piece of mechanical uselessness. And they aren't to warm the cars interior faster.
- Status
Similar threads
