leak at fuel tank after fill up
#1
Instructor
Thread Starter
leak at fuel tank after fill up
1991 S4 Auto.
The last couple times I filled the tank just before parking the car at work in the morning, I've come out to the car after a couple hours and found fuel on the ground under the fuel filler neck. The first time it happened I assumed the fuel expanded with warmer temperature. With this second time I am thinking something else is wrong. Do I have a leak in the tank that only shows when full or does this indicate something else that typically fails back there. I have only had the car about six months so I am not familiar with everything yet. Thanks for the help.
The last couple times I filled the tank just before parking the car at work in the morning, I've come out to the car after a couple hours and found fuel on the ground under the fuel filler neck. The first time it happened I assumed the fuel expanded with warmer temperature. With this second time I am thinking something else is wrong. Do I have a leak in the tank that only shows when full or does this indicate something else that typically fails back there. I have only had the car about six months so I am not familiar with everything yet. Thanks for the help.
#2
Team Owner
there is a possibility that either one of the vent hoses is leaking or that the fitting to the tank has a crack in it you can remove the cap put a rag into the opening then remove the metal ring that holds the flap in the tank to body grommet then see if you have a drain hose thats connected to the bottom of the tank grommet they usually fall off then remove the grommet and see if you can find the leak
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#3
Rennlist Member
I believe I have a similar problem with a fuel leak as well. After replacing my tank last year, due to a crack by the straps, I realized I still had a fuel leak. After looking around some, I noticed the fuel was leaking from the vent hose that goes to the carbon canister in the front fender. From age and the bend in the tube, the line gets cracked and leaks. Unfortunately, I have not been able to source another fuel vent hose. I tried the big 3 and they do not carry the line. Does anyone know where this hose can be purchased from? I hope to fix the problem, but currently I just do not fill the tank totally. Thanks
#4
I had this problem on the race car, and it was leaking at the fitting of the fuel gauge sender on top of the tank. There is a rubber "O" ring which had perished. A new o ring and a small amount of sealant and so far no repeat of the problem.
#5
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For the topic starter, it is easy to see if it leaks there. Just pull away the carpet and open up the flap under it. You can see the fuel gauge sender fitting and it has fuel around it if its o-ring is leaking.
#6
Team Owner
just a note to fit the fuel sender plastic nut it is mentioned in the WSM to soak it in hot water to expand it, then install it
#7
Rennlist Member
probably a crack toward the to of the tank where the attachment straps are. I had one there, that was only a problem when I filled up. with 2-3 less gals of gas, not an issue. try and get under the car to see where the leak is coming from.
mk
mk
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#9
Rennlist Member
I filled up my '85 for the first time and realized that I have this problem with a leak at the top of the tank. According to this old thread, there is an O-ring here that needs replacing. Can someone help me with the where and how? Here is a pic of how it looked after I got it home. I drained out about a gallon of gas and got it dried out. No longer leaking up into the interior. I need to know where the (possibly) offending O-ring is and the procedure to replace it. Any guidance is very much appreciated.
Thanks.
Thanks.
#10
Rennlist Member
The circular ring with radial ribs on it will unscrew to reveal the "O" ring. Buy a new "O" ring, lubricate it with silicone paste and screw the ring down on it after warming in hot water as described above. Before sealing everything up, it would be wise to remove and clean the sending unit and whatever else might be accessible.
#12
Three Wheelin'
could also be the vent hose that joins the tank main section to the section that goes up toward the filler neck. Since the "frame" of the car goes between the two, this hose is needed to allow the air to escape the upper part of the main tank section. Ive found these, including on my car, that this hose is dried up, fails, and leaks.
part 11 in the below
part number 92820119405
part 11 in the below
part number 92820119405
#15
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Oh and pour some hot water on it before trying to loosen it. It will expand the plastic and make it easier to open. Make sure you don't get water in your tank Maybe use a wet hot towel instead.
The hot water thing is mentioned in the workshop manual for assembly. They put the screw in some hot water before putting it on. When it cools down it can be very hard to remove. I damaged my ring slightly before I knew this.
I also had a vent hose leak that granprixweiss928 is talking about. One of the metal clamps that holds the vent hose rusted through and allowed the hose to leak. The hose itself looked pretty bad too. The Porsche hose costs like 70 euro, while a local garage of mine had the same type of hose for 5 euro. There's a nice write up on how to do it: https://members.rennlist.com/sharksk...0-FuelTank.htm
But I hope you only need a new o-ring. Much easier. It's not funny to pull the gas tank.
The hot water thing is mentioned in the workshop manual for assembly. They put the screw in some hot water before putting it on. When it cools down it can be very hard to remove. I damaged my ring slightly before I knew this.
I also had a vent hose leak that granprixweiss928 is talking about. One of the metal clamps that holds the vent hose rusted through and allowed the hose to leak. The hose itself looked pretty bad too. The Porsche hose costs like 70 euro, while a local garage of mine had the same type of hose for 5 euro. There's a nice write up on how to do it: https://members.rennlist.com/sharksk...0-FuelTank.htm
But I hope you only need a new o-ring. Much easier. It's not funny to pull the gas tank.