48Super

Fuel coming out of tank vent

Recommended Posts

OK, this problem isn't with my Buick but I think you folks can help. The  subject car here is my 1967 Cadillac but I know many Buick models of the era used a similar fuel tank arrangement.  The fuel filler pipe is located behind the license plate and comes out the rear of the tank, there is a metal vent tube located on the top front area of the tank. The vent pipe is shaped like an upside down "U" and the highest point of the "U" is 10" above the top of the tank. 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
8 minutes ago, 48Super said:

there is gurgling sound coming from the fuel tank and gas comes out of the tank vent.

 

How much gas comes out?  How big is the spot left on the ground?

Share this post


Link to post
Share on other sites

Check the fuel vapor canister?  Not sure if 67 had a canister.   Could be the source of air getting into the return fuel line.    

Edited by avgwarhawk (see edit history)

Share this post


Link to post
Share on other sites

There is no vapor canister on this car, it has a very basic fuel system. When it spits out fuel it makes a spot about 10" in diameter on the floor. 

Share this post


Link to post
Share on other sites

Is it possible there is a one way check valve in the fuel system. The return line off the pump?  Check valve stays open when shut down allowing air to get into the tank?   

Edited by avgwarhawk (see edit history)

Share this post


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

What I can't understand is how pressure is being developed in this line after the engine is shut down.

Heat with no circulation after shutdown is causing the fuel in the line to vaporize...that's the bubbling you hear.

Share this post


Link to post
Share on other sites
24 minutes ago, old-tank said:

Heat with no circulation after shutdown is causing the fuel in the line to vaporize...that's the bubbling you hear.

 

 

Then this guy shows up with a very strong answer to the issue at hand. 😃   

Share this post


Link to post
Share on other sites

Is this a recent situation?  Since this car has the two outlet fuel filter, does this problem coincide with a filter change?  How about a fuel pump change?  

Share this post


Link to post
Share on other sites

I purchased this car last March and it has done this the whole time. I don't think it is a matter of heat causing the issue. My '65 Riviera has a similar fuel system and the muffler is right up against the front of the tank and it never gurgles or vents fuel.  I may try blocking off the return line from the fuel filter to see what affect it has. 

  • Like 1

Share this post


Link to post
Share on other sites

disconnecting that line will likely solve the immediate problem ( fuel spillage) , but only masks the underlying cause. 

 

Can you source another dual outlet gas filter and try that? 

 

Share this post


Link to post
Share on other sites

 

 

2 hours ago, JohnD1956 said:

 

Can you source another dual outlet gas filter and try that? 

 

When I changed the fuel filter, it looked like it may have been the original AC GF-149 element. The car is low mileage (45,000) and these filters haven't been made for a long time. I replaced the filter with a WIX 33039 filter which is the correct part for air conditioned cars. Although the two filters are different in construction you can tell by looking at them that they do the exact same job. Out of curiosity, I may buy a NOS GF-149 and install it to see if it helps.

Share this post


Link to post
Share on other sites

Today's gasoline is more volatile than it was in 1967.  Could vapor be condensing in the vent tube and leaking out?  A few drops of fuel can make a good-sized spot on the driveway...  A full tank doesn't allow much room for expansion, which may explain why it doesn't happen when the tank is less than full?

Share this post


Link to post
Share on other sites

Not sure if already covered but considering it's an issue on a near full tank, is there a gasket between the tank and the vent tube that could be leaking rather than the vent tube itself?

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