Air gap manifolds in cold weather

fishy68 said
Hum... I can't really see an extra coolant passage running under the plenum unless it's that threaded hole in the side of the plenum. It would need an outlet somewhere. Maybe on the side not pictured. Doesn't say anything about it in the description. That must be a fairly new design if it is designed that way, or I'm behind on the times LOL.

Hi Fishy,
If you have a look at the 360deg. image, the manifold will rotate and show the underside of the manifold and you'll see the bulge run from the side of the manifold up to the front.
And the threaded opening on the side where the carb sits would be for the heater hose to connect to.
At least that's what it looks like to me.