Hi Folks, hope you all had a wonderful Easter Day----So this is what’s going on, I drove my 1986 xj6 to my mother in-laws house about 1 mile away from me, got there with no problems, but on the return home my son says Dad it smells like Gas, so we arrive home and when I look around the car I see gas leaking from the rear driver side, , I remove the cover for the tank, and can see a hose approx. 1/2’ that seems to be a vent hose (not mating to anything) and runs behind the tank and looks like it runs to the front of my Gal , and the hose be a leaking gas .Does not leak when you start her, she starts to leak after driving about 1-2 miles, what could be causing this, she has been running fine , but I Did replace a faulty fuel pump approx. 30 miles ago but she has been running fine with no leaks, -----1986 XJ6
You have two separate issues Dieman.
First, the hose you are referring to is part of the fuel vapor recovery system and should be connected to the vapor recovery tank in the C pillar. Very fiddly to put it back…
Second, most probably either your Fuel switch-over valve or one of the Fuel return valves in malfunctioning and your car takes fuel from the right tank and returning it to the left, thus overflowing the left one.
Lots of info in the archives on how to troubleshoot the tank switching scheme.
An other possibility is that If your tank was full at the brim when that happened as the fuel heats up and expands it overflows from the unconnected hose fitting.
Hope that helps,
Aristides
As per Aristides, Dieman - you have an overflowing ‘left’ (I assume driver is on the 'left side in your case)…
Quick check; switch to the other tank, run the engine - and see if the ‘leak’ disappears…
Proper test procedure; open both filler caps and run the pump. select ‘left’ and ‘right’ tank in turn while listening at the filler lid for the sound of petrol returning to the tank.
Petrol should only(!) return to the selected tank. If it returns to both tanks in ‘left’ selection - the ‘right’ return valve has failed open. If it returns to both tanks in ‘right’ selection - the ‘left’ return valve has failed open. The failed return valve must be changed…
Alternatively; fuel is only returning to one tank, but not to the selected tank in one selection. To the left tank with ‘right’ selected, or to the right tank with ‘left’ selected - the changover valve fails to switch to the selected tank. Check/ clean or replace changeover valve…
To elaborate; when fuel is drawn from a tank - the fuel pressure regulator bleeds off fuel and return it to the tanks. It must return to the tank it is drawn from, else the ‘unused’ tank will fill up from the ‘used’ tank and overflow. Fuel will in effect be gradually transferred from tank to tank - and one return valve closes of the return to the ‘non-selected’ tank to prevent this.
If the changeover valve fails to switch to the selected tank, fuel is drawn from the ‘wong’ tank - but returned to the selected one by correctly operating return valves. Again transfer of fuel and overflow, as you describe…
There may be other, more subtle faults - but the first step in diagnosis in invariably to listen to tank returns as described…
If switching tanks with the changeover switch eliminates the ‘leak’; it’s perfectly OK to run the car on that selection - while you ponder actions. When that tank gets low; you just switch temporarily to transfer some fuel from the other tank - then switch back…
You don’t need to run the engine for the testing - just the pump.
Frank
xj6 85 Sov Europe (UK/NZ)
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Thank you both very mucho, I will check her out this weekend, and if needed will replace the return Valves, I like this Old Gal, she is a solid form of old school transportation, and she looks Great
Frank,
I’m pretty sure I have the same problem with my ‘87. Gas leaks from my left (driver’s) side after I fill up the tank and drive it a while. It’s a stream of gas rather than just a drip. I can hear gurgling from under the filler cap while it is leaking gas. If I lift the cap, the leak stops. If I run the car from the right tank, there is no leak.
Does the gurgling from under the filler cap or the fact that lifting the cap makes the leak stop provide any more clues?
Your post is helpful and I’ll run the test you suggested to try to troubleshoot the problem.
Danny
A precis answer from me, no. A guide for thinking and exploration, yes.
Your car as mi8ne that is similar has three plumbing lies used for fuel and vapor.
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The supply via the pump and the selector valve to the fuel rail up front.
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The fuel return again directed to the tank selected to fuel the engine.
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The closed vapor collection system. From each tank across the body and forward to a oe way valve and a vapor cannister and thence to the engine for consumption.
I think that opening the lid either relieves pressure or vacuum and that is the force that causes the leak to stop. Which and how not yet clear.
Carl
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It complicates matters, Danny…
The banal problem is a failed return or changeover valve - causing the fuel to return to the ‘wrong’ tank. The point is that fuel must return to the same tank as it is taken from. If not, fuel is taken from one tank and transferred to the other - which will overflow when filled…
The hitch here is that opening the filler lid will make no difference. The overflow will continue as long as the pump is running - or the other tank is selected…
So where does the petrol leak out in your case, with the lid closed?
Carl rightfully mentioned the closed tank ventilation system - which is indeed affected by opening the filler lid. However, while leaking is possible, the symptoms and leak points are different…
So some clarifications seems required. Like; did you stop the engine before opening the lids - or was the engine running? And where were the leaks…?
Frank
xj6 85 Sov Europe (UK/NZ)
**
Hi Frank,
Thank you for helping me diagnose this problem!
The fuel was dripping from just behind the left, rear tire from the corner of the bottom of the fender, pic attached where it was dripping from. You might be able to see in the photo where it is wet. It was leaking both while the engine was running and after I turned ithe engine off and the key was out of the ignition. I noticed the gurgling after the engine was off, the key was removed, and while it was still leaking. I then opened the filler cap and the leak stopped soon afterward. While it was leaking I looked inside the trunk. The spare and everything had been removed so I could see all the fuel lines. There was no sign of leakage anywhere inside the trunk.
Danny
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The plot thickens, Danny…
The shown drip location only tells that the leak is higher up - ‘behind the rear wheel’ may just imply that the petrol runs along the tank before dripping down…
That the drip stops some times after engine shut-down and the lid is opened is likely a blind. It just means that the leak stops when tank level drops below the leak point as pump is stopped and fuel leaks out…
The most salient point is that at no stage should tank level rise with or without the engine running and with or without the lids opened. This is due to the return and changover valve functions; they are constructed to be open only to the tank selected - and closed to the non-selected tank…
Secondly; there are no designated outlets from the tank with the closed tank ventilation system - except the filler lid itself…
I suggest you open the filler lid and run the pump with ‘left’ tank selected. There is no need to run the engine (discouraged with a fuel leak!) - just remove air filter and prop open the AFM flap. The pump should now run whenever the ign key is ‘on’…
Watch at the ‘right’ filler lid how the leak behaves - also verifying that you can hear fuel returning to the selected ‘left’ tank. If the filler tube, ‘right’ tank, overflows with or without the leak appearing at the rear tyre - it confirms that the tank is getting fuel it shouldn’t. Watch specifically if the fuel runs down into the filler lids water drain which may account for the external leak at the rear…
Stop the pump and watch what happens - the overflow should stop and fuel levels drop. Note where the fuel level stops - it will indicate the level of an external leak. The dripping at the rear may stop when fuel is no longer running down the water drain…
It’s almost certainly a failed ‘right’ return valve - unless tests shows otherwise. The ‘right’ return valve may just not close completely, allowing fuel to return to both tanks…
It’s perfectly safe to drive on the ‘right’ tank while you consider options - which actually is, unless otherwise indicated, to replace the ‘right’ return valve.
Drive some time on the ‘right’ tank while monitoring fuel gauge’s levels briefly on the ‘left’ tank. ‘Right’ fuel level should drop as fuel is consumed - the ‘left’ should stay put.
Fuel system is somewhat complicated, hence the testing rigmarole…
Frank
xj6 85 Sov Europe (UK/NZ)
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Well, I feel a little dumb but I discovered today I was mistaken about which tanks were being used. The lights in my fuel selector button are so dim I can’t see which tanks are being used. And my eyes are so bad without reading glasses, I couldn’t read the little ‘R’ in the white band around the fuel selector button. All this time I thought when it was depressed it was using the right tank. But when I filled the tanks today and watched the fuel gauge, I realized I had the tanks reversed. When the button is depressed, it is using the left tank, not the right.
So here is what’s happening. When I’m using the right tank, fuel starts leaking from the left side. If I switch to start using the left tank, the leak stops.
So based on what Frank wrote earlier, I think the changeover valve is the cause and should either be cleaned or replaced. Am I correct?
Frank, regarding the test you wrote above about opening the filler caps and listening to see which tanks were being filled, I tried that but couldn’t hear anything from either tank no matter which position the fuel selector button was in.
Danny
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The logic is the same, Danny - just switch ‘left’ to ‘right’ and vice versa in the text…
To emphasize; the ‘left’ tank still leaks with ‘right’ tank selected - but it does not leak with the filler caps opened…??
Fuel is returned from the pressure regulator to the tanks through their respective return valves. The non-selected tank’s valve is closed - in this case; with ‘right’ selected the 'left return valve wrongly stays more or less open.
When fuel in this situation is taken from one tank, it is returned to both - and the tank not in use will fill up and eventually overflow.
That this does not happen with the tank lids open is highly contradictory - the filler lids’ position is irrelevant for the return valve functions…
The standard return valve test is to run the fuel pump and listen at the filler lid to ensure fuel is only(!) returned to the selected tank. Easy if the tanks are half full - if full, one will overflow if a returned valve has failed…
Mind you, if the ‘wrong’ tank is not full, it may take some time to fill up - but if not full; it should not leak…
Certainly, the ‘left’ (in this case) return valve is the normal suspect - but the symptoms described is bewildering…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Danny:
Yeah as to eyes. It seems I am becoming a “weak eyed” Texan. A term used decades ago, by Bob, a workmate and from my home town. Just cuz I used reading glasses, and he probably needed them but refused to be seen using them!!
As to the selector, I can’t se the marks either. so, I just memorized “right in, left out:”.
Fortunately my car’s fueling works just fine, so I just go back and forth til it’s time to tank up…
Carl
There’s been a number of times in my old ‘S’ where I have forgotten that the other tank is already drained DOH!
Also did it with a P5 Rover 3.5ltr that I used in the UK as a taxi (private hire) they had a reserve in the tank, yep did that a few times as well 
I replaced the left return valve yesterday and the car is no longer leaking!
Thank you, Frank, and everyone for your helpful advice. I greatly appreciate it!!
OMG. For two months I’ve had no fuel leak after replacing the left return valve. I was so happy that was resolved. Until today…
My left tank was half full and my right tank was full. While the car was idling in my driveway using the left tank, it started leaking from the same spot as before on the left side. I opened the left cap and could see fuel was overflowing into the overflow drain and dripping off the rear fender. So I switched to the right tank and the leak on the left stopped. But after several minutes, the right side started leaking! I popped the cap and the tank was over full. Fuel was overflowing the filler, just like when you overfill it at the gas station. It was then going out the overflow drain and dripping down the right rear fender. I looked at the gas gauge, which used to read full, and it actually had moved to beyond full.
Needless to say, to have a fuel leak issue again but now from both tanks has gotten me pretty discouraged. If anyone has some advice, I’d be so grateful.
One possibility would be a sticking changeover valve (in the wheel well next to the fuel pump.) If this sticks so that you are drawing fuel from both tanks, but returning to only one. Then you will see fuel transferring from tank to tank and potentially overflowing.
It sounds like your return valves )in the wheel wells) are working correctly.
You could try cleaning the changeover valve, which may work, or replace it. You’ll need hose clamps too for the feeds hoses from each tank or they will pour gas everywhere the moment you disconnect the hose - an obvious hazard so be prepared. That or drain the tanks completely first.
Regards,
Andy
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It’s not a fuel leak, Danny - fuel is transferred between tanks, causing overflow…
Functioning properly; fuel is taken from the selected tank by the changeover valve. Then returned to the selected tank via the return valves; the selected tank’s valve being open - the other closed.
If fuel is taken from one tank (or both) and returned to the other( or both); it effectively transfer fuel from one tank to the other (less the fuel actually used by the engine, of course).
Normally, with a tank overflowing; switching tanks stops the overflow - allowing car to be driven while remedial actions are considered. So yours is a very unusual case…
Andy outlines one failure mode; the changeover valve draws from both tanks - which is very unusual. Or both return valves has failed ‘open’ - which is equally unusual. Adding that all valves are electrically operated; ‘left’ selected - no power to either valves. ‘Right’ selected, all valves are powered - courtesy of the changeover switch.
The orderly testing is first to check fuel return; opening filler lids and listen - hearing fuel returning only(!) to the selected tank. Any fuel returning to the ‘wrong’ tank means the ‘wrong’ tank’s return valve has failed open - a positive failure test. With correct return; the fault is in the changeover valve…
With ‘left’ tank now half full (‘right’ overflows!) - select ‘left’; fuel should return (listen at the open filler lids) to the ‘left’ but not(!) the ‘right’ tank. When/if the ‘left’ is filled - switch to ‘right’ and repeat the return test; no return to ‘left’ tank. If the fuel return is correct; the culprit is the changeover - if return is incorrect in one of the test; you may have a double fault - mechanical or electric. But an ‘offending’ return valve should be changed before proceeding…
While working on this problem; there is no need to run the engine - only the pump. One way is to jump the fuel relay. The other is to remove the air filter and prop open the AFM flap - the pump will now run with ignition ‘on’…
It’s a most unusual situation - sorry for the inconvenience…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Frank and Andy,
Thank you for your quick replies! If a faulty changeover valve is a possibility, I think I’ll replace that first. I really don’t mind changing old parts since the car is 31 years old and eventually everything will need replacing. I just can’t imagine I have two faulty return valves (or two faulty anything) simultaneously, especially given I just replaced the left return valve just two months ago.
I will order a new changeover valve and will report back. Thank you again! Truly, if I didn’t have these forums and your help, I wouldn’t want to own an older Jaguar. Gentlemen, you both are amazing.
Danny
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It’s essential to first sort out the return, Danny…
…it is either ‘correct’ or ‘incorrect’ - easily tested, and independent of any(!) other fuelling faults. Ie, with ‘wrong’ return; working on any other items may be barking up the wrong tree…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Why not hook up a hose to the return line, at the engine, and a separate container. Even better, blow air into the return line and listen to the escaping air; Should show the source of the leak - return or not? Be careful.