intake manifold heat riser

Quickly heating intake manifold from a cold start aids in cold weather drivability, fuel distribution, and fuel economy. That flapper rotates once the manifolds are heated, and shunts added heat away from intake. Unlike a V8 intake nestled between two banks, the slant six intake is hanging out in the air, constantly being cooled by air flow over it.

Driving in humid weather when ambient temperature is below 40 f degrees with an unheated manifold often results in carburetor icing, real crappy drivability, and single digit fuel mileage. Also when fuel drops out of suspension in a cold intake manifold raw gas will wash down cylinder walls causing accelerated ring wear.

Rebuild the heat riser if it is not working, let it do its job, and enjoy better drivability, faster warm-ups, better fuel mileage, and longer engine life.