We were on a nice springtime drive in the country and I noticed the fuel seemed to be going down … and down and down. Rapidly. Hurried home and under the rear fender right behind the rear wheel gas is flowing out (I lost about $40 of fuel). So I isolate that tank by plugging the outlet hose in the boot and removing and plugging the switchover return valve in the wheelwell. After much fiddling and dirt in my hair I get the lower fender panel off so I can see everything. I removed the big drain plug and used the garden hose to flush out the tank. Interestingly there was a little bit of rust flakes but not near as much as I’ve seen on YouTube videos. I put the plug back in and filled up the tank with water and let it sit. No leaks what so ever. Bone dry.

It’s way easier, safer, and cheaper to test with water than gas so I wanted to ask you folks if you have any ideas before I proceed. Anyone ever have a situation like this? The exterior of the tank and from what I can see through the drain plug the tank looks to be in surprisingly good condition for being 43 years old. Thanks for any help you can give me.

Jeff

 

Jeff, were you using out of the tank that began leaking? If you were using from the opposite tank, maybe the return valve stuck and the excess gas was going back to the unused tank instead.

Dave

 

Actually both tanks are connected with a Tee into one virtual tank so if both return valves were stuck open it would just even out to both tanks. I've been driving on the one good tank for a week so I know that return valve is open. Thanks for the thought - any other ideas?

Jeff

 

One more !

The tank is fine . You were on a side hill. Teh uphill tank flowed in to the down slopetank. it overflowed. A flaw in the T adaptation.

 

Can you see if a hose is leaking?
That's what I would suspect first, as it's Way easier to change a hose than repair the tank.
(';')

 

Thanks for your responses. Carl, I was driving and the gas gauge went from full to empty in about 10 minutes. Elinor, I agree 100%, I sure don't want to pull the tank (much less buy a new one). The flow of gas was at the front of the tank and my drive is a slight incline up so I think the leak was from the front of the tank which means the fuel return hose. Where that hose joins the tank is what appears to be a pipe fitting into the tank (hex head and I can see threads). Has anyone ever removed that fitting? I don't want to take it apart and have the other side drop off into the tank. If I can safely remove that fitting and put a threaded plug in there I'll just have the return into the other tank.

I was sure when I filled the tank with water I would be able to see the leak immediately. The gas was really flowing out, like tipping a glass and pouring it out. Thanks for your help.

 

You reckoned that you lost $40 worth of fuel which at US prices sounds like around 10 gallons.
I have owned S3 XJ6s for over 30 years and have encountered all of the usual problems including changeover and return valves and overflowing tanks but have never lost fuel at the rate you quoted.
To lose fuel at the rate you encountered I would be very suspicious of a leak between the fuel pump and the engine. That would be the only way I could envisage such a quick fuel loss.
​​​​​​​Cheers

 

Bill, I know what you mean but the pressurized part is from the back of the boot up the right side of the car to the engine. The gas flowing onto the ground was about 6 inches behind the left side rear wheel. Not from the wheelwell but the enclosed portion of the rear fender. The only thing in that area is where the return hose enters the tank which seems like that would be the leaking area but wouldn't you think with the tank filled with water you would see at least some seepage there?

Remember in movies when the hero’s plane gets hit in the fuel tank and you see the fuel leaking out. That’s what it was like. Fortunately it was a hot sunny day and I parked on the up hill concrete driveway so the flowing gas ran down the concrete and evaporated. If I had pulled into the garage I’d probably burned down the house.

 

Yellow
I am a professional pilot with over 50years experience and yes fuel leaks in flight are a bit of a worry. I have had a couple with system control failures but not bullet holes.
I think your fuel return line to the left tank has let go prior to the tank.
Remember that overall the fuel system is at high pressure with a continuous flow and the system only uses what is required for the injectors prior to returning it to the tank/s.
That is the only thing I can suggest.
Cheers

 

After giving it a lot of thought I think Elinor and Bill Mac are absolutely correct and that the leak must be in the return fuel hose near the tank. To Elinor's point it’s a heck of a lot easier to replace that than replacing the tank which I can’t see leaking anyway. A lot of us have fiddled with the return valve in the wheelwell and perhaps replaced the rubber hose in front of the valve. But the rubber hose between the return valve and the tank is right next to the muffler, is 43 years old, and since you have to remove the lower fender panel to get to it probably has never been changed.

I have to order a new gasket for the drain plug and also the little strainer that fits on the bottom of the fuel pick-up tube in the tank. I was surprised at how fine the mesh was on the strainer; if there are any rust flakes in the tank the strainer will definitely keep them out of the fuel pump.

While we are on the topic, did you know that between the fuel outlet on the tank and the hose fitting in the boot there is a rubber hose? The muffler is in between the tank and the boot and there is a rubber fuel line about 8 inches long that runs right under the exhaust pipe just behind the muffler. That has to be a harsh environment.

Thanks for all your suggestions. I'll let you know how it all turns out.

Jeff

 

I wanted to close the loop on this topic. As a few of you surmised the leak turned out to be the rubber hose between the return valve in the wheelwell and where it fastens onto the tank fitting. The leaking section was in the enclosed portion below the tank. A 43 year old hose so not surprising, I guess. The good news is that it wasn't expensive to fix, the bad news is you have to remove the lower panel and drain the tank to change it. Now I’m worried about the other side.

Jeff

 

Jeff, now that you've done it once, and you know what's involved, just Change the other side before it starts leaking! You have the car parked up anyway, so while it's fresh in your mind how to do it. Go for it.

There are two classes of things not to worry about:
1)Stuff you can fix. Just Do It and stop worrying about it.
2) Stuff you can't fix. If you can't do anything about it, don't worry about it.
Life is too short for that.
(';')

 

Jeff, bite the bullet and change the other side now, you will be in a state of self-loathing if you wait until it starts leaking, which it will.

Dave

 

Elinor:

An adaptation of the serenity prayer....