Heat riser question

[chip46wis]

I am asking if someone can tell me or better show me what position the heat riser should be in---when in the open position----Mine seems to be froze and may be part of the 7MPG? Thanks

[68c10airstream]

Hi chip46wis, typical gm v8 heat riser is on the passenger side exhaust manifold, as you rev up the engine the counter weight moves rearward. Engine shut off the riser is obviously closed, and when the engine warms up the return spring relaxes and open it up with a stop pin 90 degrees open. The tin heat shield would be on the passenger side usually and warmed up the air passing through it on it's way to the air cleaner. This was part of what gm called E.F.E. (early fuel evaporative). This worked in conjunction with the heat crossover cast into the intake manifold that allowed the exhaust that couldn't leave the rh side exhaust manifold cold was forced through the crossover and out the ds exhaust manifold. This warmed up the area under neath the carb so the cold incoming fuel/air mix when it hit the floor of the intake before it branched out to each runner was warmed up quickly when cold. Once warmed up heat riser relaxed and opened up. Maybe a little info than what yo asked for, but help none the less. Good luck, Brian Fuller

[chip46wis]

thank you---very informative I must say-----My heat riser is on the driver side though and stuck------maybe a trip to the muffler shop--?
thank you friend--------

[FirstOwner69]

Originally Posted by chip46wis

thank you---very informative I must say-----My heat riser is on the driver side though and stuck------maybe a trip to the muffler shop--?
thank you friend--------

The truck heat riser was on the left side between the exhaust manifold and exhaust pipe. As I understand, its purpose was to partially block the exhaust flow from the left bank and force it through a passage in the intake to the right side that helped speed the heating of the area near the base on the carburetor. I believe only the cars had the riser on the right side. Some years also had a heat stove apparatus mounted on the left manifold that routed heated air directly into the air cleaner snorkel.

The weighted lever should be pointed toward the rear. It's closed when it's roughly horizontal and open when down. When cold, push it down and it should spring back up. GM used to make a special lubricant (I believe containing graphite in a solvent) to spray on the pivot points. I still have a partial can.

[davepl]

Thanks FirstOwner! I only have big blocks if that matters but I just went out and verified that the spring returns the counterweight to the UP position when the engine is off. Mine, even though new, seems to bind at one point though. Looks like they should be lubed from new. I wonder if anti-seize would survive those temps?

In any event, OP, if yours is stuck closed I would be very hesitant to drive it. These trucks were notorious for burning exhaust valves on the heat riser side if it gets stuck in the 'closed' position.

[chip46wis]

Thank you all----I asked a friend about the lube and he stil has a couple cans---it is stuck in the open position so except for heating as designed its ok to drive---I probably will just have it removed anyway to be safe= THANKS ALL!!!!!!!!!!