what is a heat riser? and where is it ? And how to fix ,, car will stalll and not restart when hot

Asked by Jul 17, 2016 at 12:06 AM about the 1975 Dodge Dart

Question type: Maintenance & Repair

car runs great until it gets hot...

3 Answers

70,255

A heat riser is at the bottom of the exhaust manifold,it controls the air flow from the exhaust to keep engine running cool,it is simular to the photo,this is not the one on your Dart but simular.

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70,255

You will have to remove the exhaust manifold to replace,this is the kit for your dart.

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72,455

The heat riser is a "butterfly" type valve just like the choke valve that you see on the top of the carburetor. It's located on the exhaust manifold, as TST has shown. When the engine is cold it should be closed. When it's closed a portion of the hot exhaust gases is directed up around and under the carburetor. This helps fuel atomisation and prevents ice from forming on the throttle plates of the carburetor in cool damp weather. With the engine cold, check and see if you can move the valve freely by hand. If so, the valve is good. A lot of times what happens is the passage in the intake manifold that the exhaust gases flow through gets clogged up with carbon. This can cause the automatic choke to not open up, like it's supposed to when the engine warms up. Some automatic chokes sit in a "well" next to the carburetor. As those hot exhaust gases flow under the "well" it also heats up the choke so it will open like it's supposed to. But if the exhaust passage is clogged the choke won't open and you'll get an overly rich air/fuel mixture. This can cause stalling, not starting when hot, and carbon fouling of the spark plugs. An older mechanic at a good muffler shop should be able to replace or even fix the heat riser valve. But if you can move the valve by hand it's working and you'll have to clean out the passageway in the intake manifold. Lastly, in later years, the name of this heat riser valve was changed to an EFE (Early Fuel Evaporation) Valve. It's the exact same thing except that it'll have a vacuum hose hooked up to it to help it work better. HTH. -Jim

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