The Stovebolt Site Forums The Shop Area General Truck Talk gas fumes, 46 Chev pickup

I have a friend with a 46 Chev original pickup. You can smell gas outside the truck. We have not found any leaks. I am wondering if it should have a vented gas cap?

Garret,

I'm pretty sure it has a vented cap. Without this critical little item it wouldn't run well. I don't know where the truck is stored...maybe inside a garage, but the usual source for the gas smell is the carburetor, especially after the engine is run and shut down warm.

If there are no tell-tale leaks on the ground, the source would be fuel vapors from the carburetor/engine area or a fresh load of gasoline that is heating, expanding and breathing out the filler cap.

Does that sound possible?

Stuart

Stuart,

Thanks for the quick reply. The owner kept it in a garage and did not notice the fumes. But I have the truck here now and it is a very obvious smell. He says it is a fairly new carb.

The gas cap does not look vented. But the truck runs fine.
Is there a vent on the carb (Rochester) ??

Garret

I'm not familiar with your year truck..But how about the gasket seal where the float assembly comes out of the gas tank? On my 55 the tank is in the cab and years ago it always smelled like gas...until I sealed that area of the tank.

Keith

Garret,

I'm sure the cap is vented. It wouldn't be obvious unless you turned it over and examined it. All carburetors have some type of a opening between the fuel bowl and atmosphere. After running the truck and shutting it off, latent heat can cause the fuel in the bowl to expand and dribble into the intake manifold. This can cause vapors to rise and exit the carburetor giving you the gas smell.

Does the truck have a air cleaner on it. I wonder if it has the phenolic heat spacer between the manifold and carburetor? Unless it drips and makes a mess, sometimes it's part of what comes with owning one of these old girls.

Stuart

Stuart,

Yes, the stock oil bath air cleaner is there, as well as the spacer under the carb. The gas cap has a tiny hole off to one side, underneath. It looks like it has been on for a long time. There is old gas in the tank, about 1/4 full.

Garret

Gas tank area all seems dry.

Garret

My 46 has the same issue only right after I fill the tank all the way. I have replaced the sending unit gasket when I changed the sending unit and it is dry as well. I have not found any leak anywhere but still get fumes. Mysteries of owning an old truck I guess.

Could have a leak in the lines somewhere? Especially if it is like my '54 and has a rubber flex hose with fittings that attach the sending unit to the fuel line.