Gas smell with full tank

I know that there have been discussions on this topic before but they have mainly been with the later C3's. My '69 always smells like gas when the tank is full after a drive. The smell goes away until I drive the car again and then its back. This continues until I'm below 3/4 of a tank.

I've been over every inch of the fuel system from the carb all they way to the right rear tire and I've never found a leak. The gas tank is not leaking at the seam and I have not been able to find a substanial area of wetness on the outside of the tank.

Does a '69 have a charcoal cannister? Is there a gasket between the filler neck and the tank body? (this is my best guess as to where some seepage might be occuring) I haven't seen any evidence as to leaking fuel lines. Does anyone else have any suggestions?

The 69 has a vented cap and no vapor canister. Mine smells a little with a very full tank, but not much after that. I have a new cap-less than 1000 miles. I would make sure the cap was sealing well to start with.

Same here, gas smell when the tank is full. My cap is also in question, just haven't got around to getting a replacement. One other note is if the cap is leaking fuel it is going around the fill neck onto the collar and then running down the overfill tube. I guess the nest time you fill up, you could take a ride, when you stop, make a point to check up by the cap, I have seen my wet so I know its sloshing in the tank coming out the top and running down. And I Still wonder why I can't get more than 10 MPG , couldn't be that way I drive also? , ot a chance

Dave
Mr69vett

I have seen wetness on the bottom of the cap but I have never seen any around the collar where the overflow when filling is designed to drain off. The cap does appear to be an original so I think I'm going to try replacing it.

Does anyone know if the filler neck has a gasket between it and the tank?

I just recently joined this group, and I don't know if you still have the problem or not,but I had a gas smell when I had a full tank and/or turned corners that caused the gas to slosh in the tank. I discovered gas had leaked out a separator assembly, which is a small black plastic box containing a check valve and mounted on the driver's side of the gas tank. It's connected to the return line from the fuel pump and to the fuel tank by rubber hoses.

In my case, the separator box was leaking at a joint in the box, leaking gas down on the exhaust muffler (and could have been a major problem). So I removed it, after first removing the spare tire container, took it apart at its joint, cleaned it and reglued it with a gasoline resistant glue.

It hasn't leaked since.

Does anyone know if a '69 has this?

Rick, I just looked thru my assembly manual and yes there is a gasket between the filler and the neck. I have a part # 0f 3826417, not sure if that will be a good GM number though. Looks like there are 8 bolts from tank to filler neck. Good Luck.

Dave
Mr69vett

rick, only Corvettes that had the "charcol canister" had this 'black plastic seperator". They vented to a 1/4" steel line that ran along the driver's side frame rail to the charcol canister. The car's that also had these charcol canisters had "SEALED" gas caps(late '71/'72 ). You may have such a small leak(like happened with my '75)that you'll only smell the vapors and NOT see liquid. Could be as simple as a loose or rusted fuel line clamp, to a very, very small age crack in one of your rubber fuel lines, either supply(the larger one) OR your return(smaller line).

Paul, I agree that it only takes a small leak to create a lot of fumes, but, why does it only happen over 3/4 of a tank? I would think that if hoses where the issue I would have an odor regardless of tank level.

Once the level in the tank drops, there is no smell at all.

So, I just did a search on "Gas Smell" here and found this thread.

My 79 does the same thing, and it is in the shop right now for that very reason.  The mechanic did in fact determine that the tanks leaks at the top when full.  I still have to speak with him directly, in about an hour.  I will reply again when I get more detail. 

One of the things I want him to be careful about, is looking for a build sheet!