A large number of years ago, my fuel level sender quit and I had a dealership replace it. A number of years later, I started having problems with fuel vapor/smell after topping off. I didn't connect the two events until I finally checked off my list, the (main) gasket replacement.

The tank also has a separate vapor return port with a gasket, but in my case that was not the problem.

The blue outbound gasket still retains the shape of how it had slipped out of the groove. I did not know what the problem was ahead of dropping the tank, so I procured the black one. Since the gasket was not sealing the hatch, if one were to fill up the tank PLUS tube to the door, the fuel would then leak down to the level of the failed gasket.



Problem is that the gasket diameter is a bit too small and the curb is a bit too dainty to hold the gasket in place. You can see residual marks where the gasket had spilled over the curb. Therefore I applied gasket maker to the groove to make it tacky and retain the gasket in place while I tightened down the hatch. A bit tricky, and I had to fuss with it awhile, I see why the dealership failed.


Here, the plumbing details on an '89. Other years may vary. DO NOT break anything as most parts are NLA.


As a side bar, current smog station checks will test the integrity of the gas cap, but not whether your tank actually seals, hence a useless test. However, modern cars DO test themselves for whether the fuel system is actually sealed, and will report via OBD2.

So...,
this fix had restored my range by about 5 miles, a significant number when you are carrying a gas can along a lone highway, in the desert heat, robbers slowing down to take a look.

 

That was the condition of my gasket from the factory. I was able to put it back into position and tighten the ring, and it kept its seal until I got into it again.