Vent line in my 76

[76crewcab]

Hi for some reason the vent line in my 76 k25 has fuel coming out of it and it just started. Any ideas would help thanks

 

[bucket]

Do you have just the short style vent right on the tank, or does your vent line go all the way up to a canister under the hood? Where does the exhaust exit on your truck?

 

[76crewcab]

Just the short style

 

[bucket]

Just the short style

My guess is excessive heat buildup, although I'm not sure why the gas would actually be coming out the vent. It should only have to relieve pressure (gasses).

When I got my K5, it would hiss and produce terrible gas fumes from the fuel cap after a long drive. If I removed the cap, it would relieve an enormous amount of pressure. The K5 has a rear mounted tank and my exhaust ended right before the rear axle. I know the exhaust was heating the tank, but I found out my vent was clogged and after clearing it out, it no longer built pressure in the tank.

So my guess is that there's enough pressure buildup that the fuel is maybe boiling over in the tank and puking out the vent. Maybe try running with the fuel cap removed to determine if it's a pressure issue.

 

[76crewcab]

Maybe but it’s has never done it before I have had the truck the last 7 years and just replaced both sending u it’s and now it is only doing it on one side which doesn’t make sense to me

 

[bucket]

Hmm. Is it just a 3-port switching valve, without return lines?

 

[76crewcab]

Hmm. Is it just a 3-port switching valve, without return lines?

Six port