: Overflowing Gas Tank

09-17-10, 05:06 PM
My original gas tank sprung a leak a few months ago, and I recently had the tank replaced. When I tried to fill the new tank, I ran into a problem where it would overflow every two gallons (and yes it was empty). I had the shop put another new one in, under warranty, and this one is doing the same thing. They say it's normal and that I have to fill the tank slower.

The problem is that the after market, OE replacement, tank isn't venting properly. Evey two gallons, gas gets backed up into the filler tube and then starts spraying out, like a fountain. Has anyone else had to replace their gas tank and have you had this problem? Is there anything I can do get the tank to vent better?

09-17-10, 06:16 PM
FWIW, when you are filling the tank, do you have the nozzle shield pressed tightly onto your filler pipe?, or can air get around gas nozzle and your filler pipe?.

09-17-10, 06:24 PM
It does the same thing whether the vents are blocked by the shield or if the pump nozzle is only partially in the filler tube. The place even pried the openings of the vents open more, and it didn't make a difference.

09-17-10, 06:38 PM
could something be obstructing the filler tube? maybe down where it connects to the tank?

09-18-10, 01:04 AM
^No. The gas will go into the tank once the air gets pushed out. It's just really annoying to have to remove the nozzle at every gallon, to let the air out, so it doesn't overflow.

I was thinking, what if I disconnect the fuel tank line to the vapor canister? I don't think I rally need it. Would that be enough to give the tank another vent?

09-18-10, 01:10 AM
I'm kinda stumped on this problem, maybe the new tank really does require slower filling. I dont think disconnecting the line is gonna make much difference but it worth a shot. Maybe a different brand of tank?

09-18-10, 12:05 PM
Same problem with new tank replacement on my 88. I just have to gingerly keep the flow low.

09-18-10, 04:06 PM
Could this possibly be the problem of the gas station pump, have you filled up at more than one garage?.

09-18-10, 06:13 PM
I have the same problem at some Gas stations. others fill just fine. and I have an original tank.

09-18-10, 11:58 PM
Could this possibly be the problem of the gas station pump, have you filled up at more than one garage?.

It happens where ever I go. The tank even overflowed when the guy at the radiator shop was filling the new tank.

If I disconnect the vapor canister, do I have to worry about the flammable vapors in the engine compartment? The canister vents the fuel vapor into the carburetor when the engine is turned off.

09-19-10, 12:49 AM
Oh yea. I dont have my vapor canister hooked up and it smells INSIDE the car after about 25 minutes. I can also hear the line hissing after I turn the car off. But you can try it to see if your problem is vent related.
Edit: The car that I dont have it hooked up in is the 500 that has an electric fuel pump with a regulator on the line. Maybe it will be different for a manual pump.

09-19-10, 08:06 PM
^Between the hole in the tank and the slight drip from the filter housing, I've gotten quite used to the smell of gasoline.

09-20-10, 01:05 AM
The best I can offer is to try a different brand's replacement tank. If your first one didn't do it, there's no reason the replacement should and unless all replacement parts are made the same, this may solve it. This however, is not cost-efficient in any way.

Oh well, my tank ALWAYS does that, due to the fill pipe being beneath the bumper.

10-11-10, 11:13 AM
I really need a solution to this...

The shop is refusing to put another tank in (also they don't carry different brands) and I don't have the money to buy another new gas tank. They've looked at it and say there isn't anything obstructing the filler neck and that there is no reason why it's not filling properly. Disconnecting the charcoal canister didn't help.

The problem is getting worse. Now it randomly overflows with no relationship to how many gallons I put in. Holding the trigger on the pump down far enough to just turn on the pump is enough to cause gas to spew out of the filler neck. It took me 20 minutes to fill the tank this morning because it would overflow almost every time the pump started.

Anyone out there with a fix?

10-11-10, 12:41 PM
You may have to contact the maker. What exactly makes a pump stop? Does a pump actually sense the fluid touch the nozzle?

10-11-10, 02:44 PM
Here's a wikipedia article: http://en.wikipedia.org/wiki/Fuel_dispenser

This is a quote from the article: "Most modern pumps have an auto cut-off feature that stops the flow when the tank is full. This is done with a second tube, the sensing tube, that runs from just inside the mouth of the nozzle up to a Venturi pump in the pump handle. While the tank is being filled, air displaced from the tank is drawn up this tube. Once the fuel level reaches the mouth of the sensing tube, air is no longer drawn up the sensing line. A mechanical valve in the pump handle detects this change of pressure and closes, preventing the flow of fuel."

Sven, I know you're so super technical, I hope you find the solution since it sounds like quite an annoying problem. Good luck, Dave

10-11-10, 04:59 PM
I was just watching sliced and they were cutting into a fuel pump and basically described the same method of automatically turning off the pump.

I’ve noticed that the tank starts spewing when the pump shuts off. If I manually shut it off for any reason, I get a torrent of gasoline in my face.

10-11-10, 06:24 PM
hmmm maybe the flap inside the filler neck is too far down and the nozzle isn't opening it or its defective. try sticking a long screwdriver down the neck and see how far down it goes before touching the flap.or maybe the new tanks don't have a vent in hopes that it will save on fuel from evaporating. when i fill up my jeep it does the same thing some times i have to use a screwdriver to hold the flap open while filling because the nozzle is too short.

10-11-10, 08:34 PM
^I'll look into that. I know the old tank had that flap right at the top, but I haven't looked to see where it is on this one.

The new one does have vents, they just don't work as well. If you look at your gas tank, the two slits above the filler opening are where it vents from. Supposedly the filler neck is divided in half on the inside; the bottom part is where the gas goes in, and the top is where the vapors are vented. I don't know where the divider ends or where it is supposed to end, but it seems like the aftermarket filler neck has the divider end too soon, which is allowing liquid gas to back up in the tube.

10-11-10, 08:49 PM
Take it back to the shop that installed the tank, give them 20 bucks and tell them to go fill it up ;)

10-11-10, 09:05 PM
^Why should I give them $20? For my inconvenience, they should give me the key to the register and look the other way...

10-11-10, 09:17 PM
lol, the 20 isn't for them, it is for them to get some gas so they can see how f'd your tank is.

10-11-10, 10:32 PM
When you are filling the tank make sure hose nozzle is straight up and down .. and not tilted a little sideways... I have found this makes a big differance. let us know if it helps...

10-12-10, 12:05 AM
I didn't think about that. The new tank is shorter than the old one, so I have to put the pump nozzle in at more of an angle to make it clear the opening in the bumper.

10-12-10, 05:40 PM
I had an Olds that did that. It would actually shoot fuel back out at ya. I always blamed the vent being clogged or kinked but the car died before it drove me crazy enough to fix it. I hope you get it figured out because it is very aggravating.

10-15-10, 09:58 PM
Here's a tank for sale for $60 near me. I dont know if your looking or if its a good deal but if you want, I can go grab it for you and ship it. Its right down the street from me.
Doesnt have your car listed but it should be the same, maybe it will be better.

10-15-10, 10:52 PM
^I appreciate that, but between school and unemployment, I can't even spare the $60 right now. If worse comes to worse, and I can't figure this out, I'll get a used one from a junkyard, and clean it and coat it with sealer (just to be sure). Thanks anyway.

10-15-10, 11:46 PM
Ever thought of bending the vents a bit more open? Also ever tried blowing compressed air in to see if they work or using a coat hanger to see if there is a blockage?

10-16-10, 11:39 AM
How about just cutting off the filler neck, taking out the baffles, then putting it back in place with a rubber section and a couple of hose clamps? Many cars have filler necks that are separate from the tank. You can get fuel rated hose at any parts place.

10-16-10, 05:48 PM
My hearse has a separate rubber hose thing that takes the gas tank and reroutes it to a gas door on the side of the car like other cars.

10-17-10, 11:39 AM
How about just cutting off the filler neck, taking out the baffles, then putting it back in place with a rubber section and a couple of hose clamps? Many cars have filler necks that are separate from the tank. You can get fuel rated hose at any parts place.

Then how would it vent? Would I have to extend the divider in the pipe to the top of the rubber hose?

I've tried the coat hanger. There didn't seem like there was anything blocking either the vent or the fill hole, and I could work it almost all the way in. What's really blocking the filler tube is air; the tank fills with air that can't escape, because the vent fills with gasoline.

10-17-10, 12:53 PM
Did they kink the vent hose on top of the tank when they installed it?

10-17-10, 01:33 PM
^ I specifically asked them to check for a pinched hose, but they insisted on replacing the new tank instead.

According to my FSM, there are only three lines that come out of the tank; fuel out, return, and the canister purge line. There is no vent hose on the top of the tank, so everything needs to vent out the filler tube. I tried disconnecting the canister purge line at the engine, but that didn't help. Do you think it would help if I disconnected it from the tank?

10-17-10, 03:33 PM
Honestly, I have no idea. Don't want to speculate and have you waste your time.

Have you checked for a trouble flow chart in the FSM?

IMO, you need to go back to the shop, drop off the car, and say "call me when this tank I paid for works properly".

Robin Banx
10-17-10, 06:25 PM
^What Jay said. I've never seen a Cadillac from 1979 to 1987 toss gas back out of the tank on a fill up. Parts cars, would-be parts cars and the three I have left (the '79 Frankenstein car, the 81 Junkyard Dog and my 83 FWB) all take fuel at wide-open nozzle. I can't imagine what is going on in your tanks to blow the gas back on you but the folks who sold them to you need to be involved in the solution.


10-17-10, 06:38 PM
I would bring it back and simply tell them that it does not operate as it should, and that since they were the ones that put it in, they should provide you with a solution. Obviously, it is not operating according to the way it should, so there is a problem.

If I was a mechanic, and I used a distributor that sold me a radiator that, for example, did not circulate coolant properly, it wouldn't matter to me if that's the part that they said to use.

10-26-10, 04:34 PM
I didn't really pay close enough attention to the original tank to notice all of the differences the new tank has. I was in the junkyard today and they had one Brougham, an '89, and I happened to have my camera for an unrelated reason, so I took a picture of the filler tube. The first picture is of the one in the junkyard and the second one is of the new tank on my car:



Is the first photo how the OE filler tube is supposed to look? Would drilling those holes make any difference with the replacement tank?

10-26-10, 06:19 PM
that first picture looks like how my filler is...I would assume that the slits in the new one would work the same but what is puzzling me is why yours doesn't have the little spring loaded tab at the mouth? hehe

10-26-10, 06:27 PM
Because it was made in Mexico...