Heat-control valve

A valve which is controlled by temperature changes. When the ambient temperature is cold or the engine has not warmed up, it is closed so that some of the hot exhaust gases passes by the intake manifold to pre-heat the fuel mixture going to the cylinders. As the engine warms up, the valve opens up and no exhaust gases pass by the intake manifold. If the valve does not operate properly, the engine has difficulty in start up or the fuel may cause vapor locking.