48Super

Fuel coming out of tank vent

Recommended Posts

The  subject car here is a 1967 Cadillac but I know many other GM models of the era used a similar fuel tank arrangement.  The problem is that immediately after shutting down the engine after a drive when the fuel level is near maximum, there is gurgling sound coming from the fuel tank and gas comes out of the tank vent. I have verified that the tank vent line, connecting hose and tank vent nipple are all clear. Also, I've installed a new correct, non-vented gas cap as the original had a leaky sealing gasket.  This car has A/C so it has a fuel bypass line connecting the fuel filter and tank.  Out of curiosity, I disconnected the line at the filter and  attached a hose to it. I blew air into the hose (lung power only) and in a short time I heard the same gurgling sound and a small amount of fuel came out of the tank vent. Based on this result, I believe the cause of my problem has something to do with this return line. What I can't understand is how pressure is being developed in this line after the engine is shut down. I would appreciate hearing from anyone who may have solved a similar problem.

 

Thanks!

Share this post


Link to post
Share on other sites
2 hours ago, 48Super said:

The  subject car here is a 1967 Cadillac but I know many other GM models of the era used a similar fuel tank arrangement.  The problem is that immediately after shutting down the engine after a drive when the fuel level is near maximum, there is gurgling sound coming from the fuel tank and gas comes out of the tank vent. I have verified that the tank vent line, connecting hose and tank vent nipple are all clear. Also, I've installed a new correct, non-vented gas cap as the original had a leaky sealing gasket.  This car has A/C so it has a fuel bypass line connecting the fuel filter and tank.  Out of curiosity, I disconnected the line at the filter and  attached a hose to it. I blew air into the hose (lung power only) and in a short time I heard the same gurgling sound and a small amount of fuel came out of the tank vent. Based on this result, I believe the cause of my problem has something to do with this return line. What I can't understand is how pressure is being developed in this line after the engine is shut down. I would appreciate hearing from anyone who may have solved a similar problem.

 

Thanks!

I have a 63 Pontiac Catalina and a 69 Pontiac LeMans. They both have a fuel return line to the tank. The 63's fuel filter has the returned line to the tank. The LeMans has the return line built into the fuel pump. Non A/c cars don't have this fuel return line. It's purpose is to constantly recycle HOT fuel to the tank and bring fresh cool fuel to the engine to prevent vapor lock. The 63 has a gas cap on the left rear fender fairly high and after filling and driving home you can hear the gurgle. The LeMans and all "A" bodies have a terrible fuel fill location, it's behind the License plate and low. That car doesn't gurgle but If you fill it to the max on a hot day the fuel will expand where the fuel will run out of the vent tube. Also at the drag strip on my LeMans  if you have a full tank for traction you will leave a trail of fuel out the vent tube for about ten feet when you leave the starting line. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now