Fuel Leak in my '71

[j10nbom]

Hi All, I searched but I'm still trying to determine the cause of a pretty big fuel leak yesterday in my '71. I filled up with gas before I started driving any real distance. I went a few miles down a fairly windy road and started smelling fuel. So I pulled over the side only to find a sizable puddle of gas in front of the rear passenger side tire as well as around the fuel filler inlet after I opened the flap. To be on the safe side I killed the engine and I had the bus towed back to my garage to deal with it. I noticed after towing the bus back that a bunch of fuel puddled on the roll-up tow truck in a similar spot (many wide turns taken, bumps, etc.)

I believe the gas cap is original so I thought possibly that I overfilled it and fuel may have been sloshing around and escaping that way. I also thought maybe because I moved the fuel filter out of the engine compartment and under the bus where it comes out of the tank...maybe that was the issue? But the line appeared to be appropriately clamped and no evidence of fuel leakage. I'm leaning towards the gas cap and overfilling it being the culprit but I know some of the fuel lines are likely to be originally and I don't believe the EVAP canister and lines are present. I'm pretty confused to be honest and couldn't determine the exact source yesterday.

So any thoughts, help, or advice would be greatly appreciated!

[alman72]

it is the line that goes from the fill port to the tank. cracked, and damage escalates when you shove the gas nozzle in deep.

[sjbartnik]

Gasket in fuel filler cap.

Filler neck.

Vent lines.

Probably gonna want to pull the firewall panel to get a good look at what's going on with the filler system.

I mean the easiest thing would be if the gasket in the cap is bad. But beyond getting lucky and fixing it with that, good time to pull the engine out and the firewall panel and see what's up.
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[alman72]

on the filler neck, the repop I read is crap. Skills will tell you. he cut a hole to have easy access because it needs replaced every couple of years. Someone else on here took the filler neck to the FLAPS and found an off the shelf piece that did the job, but time will tell. I don't recall if they had to add an elbow.
someone here will correct me, but is there not a round pie plate cover in the engine compartment that pops out that the OP could have a peek?

[Angus II]

Hello,
Fuel/gas cap seal... most likely.
Filler tube to tank, doubt it. You wouldn't get fuel back up stream at the fuel cap area.
Yet, maybe a vent line..
Cheapest fix is try another fuel cap or seal. Other wise you may be pulling your engine if it's the filler too tank hose piece.
Hell, just fill to half a tank then, problem solved... No...

[j10nbom]

Sounds like the cheap fix is to throw on a new gas cap on and not overfill it. I'm probably going to end up dropping tank because I have to replace the sending unit anyway. I think that'll be a good opportunity to replace it all with new rubber.

[Wildthings]

Could be a block tank ventilation system that is forcing the fumes to find another way out and carrying liquid gasoline with them.

[busdaddy]

Mine pulled that move a few years ago when the OG filler neck hose shrank enough to partially pull itself off the tank end.
New hose, vapor line connectors and a sender internal ground rework and it's good for another 45 years
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[aeromech]

The smoking gun here is that it did it after you filled the tank. When the fuel backs up into the filler neck that forces fuel out the vents that live on the left and right side of the top of the tank. This usually isn’t a problem unless they are old hoses and leak.

The solution is:

1) pull the engine, then the firewall, and replace the vent hoses or

2) only fill the tank to less than full

You can live a long time only filling to 3/4
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[Zed999]

[j10nbom]

All really good info here. I guess I'll be putting the fuel line/sending unit repair on the list a little sooner than I thought. Granted, I could always keep the fuel level a bit lower and carry a jerry can on me.