I have an 81 F150 4x4 with a C6 351M

I have been having an on going problem with my rear fuel tank leaking from the top when any gas is in it (as little as 5 gallons) while the truck is running (doesn't leak if the truck isnt running). Does anyone know what could cause this?

Thank You,
Josh

 

My 81 rear tank had the same symptom, my problem was a rotten rubber fuel hose between the tank and steel line.

I would crawl under there and replace ALL the rubber fuel hoses as they're all 30 yo and in pretty much the same condition.

 

Okay i will do, does the tank have to be dropped and is all the hose the same size?

 

I dropped my tanks although some will say it can be done without doing that but I think it'd be more of PITA that way.

I don't remember the fuel hose sizes but I *think* they were all the same.