Rear Drain Line

[craigamuir]

Last year my 2000 LS developed a problem when you tried to fill it with gas. As you pumped the gas in, much of it just sprayed back out. The dealer said that the charcoal cannister and the fuel filler valve needed replacing - $900. I paid for the repair.

A few weeks ago the same problem repeated (or so I thought). I took it to a different dealer and told them it better not be the charcoal cannister or fuel filler valve. They pulled the shop manual on the car and began to search for the problem. 4 days later they called to say that they had solved the mystery.

Apparently there's a rear drain hose for runoff water around the trunk area. The air release for the gas tank also vents into this drain line. Putting gas in the tank vents the air in the tank into the drain line. If the drain line gets clogged as mine was, the venting air causes the backed up water to gurgle and then spray out a drain hole just above and to the left of the main fuel filler hole. This makes it look like gas is coming back out when you put it in. Actually it's the backed up drain water in the line.

The second dealer blew out the obstruction in the drain line with an air hose and now the car seems fine. The dealer said that they had never encountered the problem before.

[SKperformance]

It is illegal for any gas system to vent into open air that is why you have charcoal canisters.

So a line used by another drain is a lie.

Most problems with back spray is from the type of pump used and the angle the pump is held.

Not all gas stations are the same and some will cause the pump to keep shutting off or spraying back by the angle of the pump nozzel.

[craigamuir]

It is illegal for any gas system to vent into open air that is why you have charcoal canisters.

So a line used by another drain is a lie.

Most problems with back spray is from the type of pump used and the angle the pump is held.

Not all gas stations are the same and some will cause the pump to keep shutting off or spraying back by the angle of the pump nozzel.

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Given that we're talking about car dealers, you certainly could be right.

I gather from the dealers discussion that the tank vents through the charcoal canister and into the drain line. There's no reason you couldn't design it that way, I guess. Houses use common drain-waste-vent pipes.

I used 4 gas stations of different brands and the problem occurred at all 4 regardless of the angle of the pump handle. Previously, I had had no problem with gassing up at these stations. Besides, the liquid does not come back out the filler pipe but rather a 1 cm wide "blow hole" above and to the left of the fuel filler hole. They said that this is an outlet of the vent system (presumably for tank vent air that's come through the cannister). I don't see how holding the pump handle the wrong way could cause gas to go in the filler pipe and back out the drain-vent pipe .