Fuel pouring out filler neck!

mkIIIman089

Supramania Contributor
Mar 30, 2005
3,061
0
36
Ohio
Okay guys, got a bit of a problem that seems simple but I can't think of any logical reason as to why its happening. Here goes:

Last week I noticed that the paint under the filler door was bubbly and soft, obviously fuel had been in contact with the paint and it had to have been more then a couple drops that would have just evaporated. So I'm pissed, and think it was MAYBE the couple drops that came from the pump last time I filled it.

Yesteday, I filled it again from E, 15.5 gallons went in, when the pump clicks I never add any more, it goes in perfectly fine. From there I drove to my appt (approx 5 miles) no odor, no fuel leak. Today, I drive to school (approx 10 miles, stop and go ~30 minutes) park, no odor, no leaks. I go out to my car during lunch (about 4 hours later) and clearly there is a fuel smell in the cabin, so I look at the gas door and there is fuel RUNNING down the side of my car, enough to make a very small puddle on the ground. I pull the gas cap, fuel spills out of it, and the filler neck is COMPLETELY full. I'm assuming this is the 2nd time this happened now, since it runs exactly down where the paint is stripped.

Mods that could effect it:
Charcoal can removed and line plugged, gas cap drilled for vents. Has been like this for nearly a year now and I have NEVER had a problem like this before, whenever I go to fill it up, there is never any pressure or vacuum on the tank, its always completely neutral; so the cap vent does work.

Sorry for the long post, I feel its mostly relevant though, its just incredibly irritating to see my paint ruined by this and I would like to remedy it.

Thanks for any suggestions!
 

jimi87-t

Active Member
Oct 12, 2005
1,126
4
38
Colorado Springs
Well your tank is definitely building pressure, and not being able to release it properly. With the cap being vented, and the filler neck location on our tanks (it mounts a little below the top of the tank) I could see with a full tank that the pressure is pushing the fuel up the neck. I bet this doesn't happen on 3/4 or less fuel does it?

Best solution (other than getting rid of the vented cap) is to not fill up the tank, only fill 3/4 full, or put your charcoal canister back in.
 

bgrieger

New Member
Mar 30, 2005
206
0
0
52
Toronto
Yup, pressureization...you capped off the only place where the air can get out from, so when it compresses now, the only thing it can do is push the fuel out the neck...until it gets low enough that the neck has air under it.

Now you know why most don't cap the line, but run it under the car. If the vapours concern you, and you still want a cleaner engine bay look, get a canister from a honda or such as they are about the size of the AC drier...discreet, and your problem is solved.
 

mkIIIman089

Supramania Contributor
Mar 30, 2005
3,061
0
36
Ohio
You guys are actually not the 1st who mentioned that exact scenario to me, I basically ran out of daylight to be able to test it though. AFAIK, yes, its only soon after I fill it up. What you are saying does make sence, but I am a little confused on a couple aspects of that.

Why, after running like this for so long, would it only now start to overflow now? Assuming it is from pressure build up at the top of the tank.

Again, assuming you are correct... When I fill the tank, that gap of unreleased air would still be there and the pump would just click off earlier then if that air had been vented out the charcoal canister line right? Effectively NOT filling the tank to its full capacity.

All night I have been thinking of a better way to vent the top of the tank, running it under the car would be easiest but I would like to try something a little cleaner if I can. I'm not concerned about vapors, just as long as they don't get in the car or in the engine bay.
 

Figit090

Fastest mk3 GT4 1/4 mile!
Jan 7, 2006
1,835
1
36
Humboldt County
based on quick thoughts.....

my first guess would be you filled up and the cold fuel caused any air in your tank to contract, and as your car heats up from the air around it and the hot pavement, the air (and gaseous fumes) inside (which has now increased in volume because you used some gas traveling, pulling air in) expands and the design of the tank (as said before) forces the pressure to be released by forcing fuel back out the filler.

so....i would suggest fixing it or running from halftank to halftank :D

hope that makes sence....
 

jimi87-t

Active Member
Oct 12, 2005
1,126
4
38
Colorado Springs
mkIIIman089 said:
You guys are actually not the 1st who mentioned that exact scenario to me, I basically ran out of daylight to be able to test it though. AFAIK, yes, its only soon after I fill it up. What you are saying does make sence, but I am a little confused on a couple aspects of that.

Why, after running like this for so long, would it only now start to overflow now? Assuming it is from pressure build up at the top of the tank.

:dunno: there are too many variables, like maybe the gas station you fill up at allows the tank to fill more before "clicking off" than it use to.

Again, assuming you are correct... When I fill the tank, that gap of unreleased air would still be there and the pump would just click off earlier then if that air had been vented out the charcoal canister line right? Effectively NOT filling the tank to its full capacity.

No,
plus there is a small hard line in the neck that curves up into the tank that lets the would be traped air out into the filler neck.
 

mkIIIman089

Supramania Contributor
Mar 30, 2005
3,061
0
36
Ohio
OK, well I have a plan. I didn't realize that the vent has a valve on it that prevents liquid fuel from escaping through it which makes it MUCH easier since I don't need to worry about keeping the vent tube above the highest it could fill with fuel. Maybe that will be the project for this weekend...