What could this random tube attached to the exhaust be?

[Chris64]

Surely someone can explain this mystery tube to me. It's hose clamped to the exhaust for some reason. It's not drilled out or anything if you look down the tube. It's just clamped to it and barely hanging on. Chesterton's-random-exhaust-tube. It's better to figure out why it's there before removing

Excuse the rust. I'm working on it.

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[Redfish]

It almost looks like a poorly fabricated heat riser. The truck originally had a heat riser that ran from the exhaust manifold straight up to the neck of the air intake duct of the air cleaner. Maybe the Previous Owner was trying to recreate that?

 

[Radiohead]

That's what I'm seeing too

 

[Grit dog]

99% sure someone fabbed up a connection for a carburetor heat riser for an OE air cleaner like was present on original OE exhaust manifolds.

 

[Radiohead]

I find it ingenious. I have to fab up something similar when the headers go on. Next spring...

 

[Chris64]

It almost looks like a poorly fabricated heat riser. The truck originally had a heat riser that ran from the exhaust manifold straight up to the neck of the air intake duct of the air cleaner. Maybe the Previous Owner was trying to recreate that?

What function did this serve? Should I complete this?

 

[Radiohead]

On the stock air cleaner housing there is a diverter valve that has some of that metallic flex tubing attached that goes onto that piece of pipe. When it's cold, vacuum is applied to position that valve, allowing heated air to go into the carb and when operating temp is reached, that valve will retract to allow "cold" air to the carb.

I could have the vacuum application backwards, but that's how it works and why.

Being in San Diego, you may never need it, but go anywhere cooler, it will help the cold driveability. I'd put it back to operational.

 

[saltdog]

Its for the Thermac system- see https://www.gmsquarebody.com/threads/thermac-system.11855/page-2

 

[RaisedK5]

Similar to this.

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[77Matt]

Does exhaust actually come out of that pipe? The heat rise isn’t actually connected to the exhaust but sits up against it so hot air rises.

 

[emoze]

in CA, pre-76 is exempt from smog inspections; just remove it & enjoy the truck ... (unfortunately my 84 is not exempt)