Fuel smell in boot and rest of car on hot days

[SimonR]

Hello all,

I've been trying to trace this problem for a little while and it's got me a bit dumbfounded.

I should start by saying that when the car was in for its recent extensive bodywork job, the fuel tank was removed and I gave it a thorough check over as I was expecting to find rust and perforation which would explain this problem, however, the tank was in perfect shape and categorically not leaking. My previous car had a leaking tank, which turned out to be a crack in a spot weld, where a baffle was attached to the floor of the tank - it also had suspicious rusty areas on a couple of the seams so I used a POR 15 kit from Frosts which solved the problem once and for all.

The issue is that there is often a smell of fuel, particularly while the car is in motion. I took it to a car show this weekend and on the way there (the weather was relatively cool) there was no discernible issue, however, on the way back, after it had been standing in the afternoon heat after about 10 minutes of driving, it smelt like there was fuel gushing out somewhere - really strong. I stopped and checked the visible pipework in the boot (removed the spare wheel and also checked the fuel filter) but didn't find anything leaking. We opened the windows to try and let the vapours escape, but this seemed to make the problem significantly worse - I guess the air flow was sucking the vapour out of the boot. When we arrived home, everything that we had stored in the boot smelt of fuel.

I've just had a free hour so took the boot area apart, removed the battery tray, reconnected the battery and ran the car - nothing seemed to be leaking, but I've tightened all jubilee clips for good measure.



One thing that I noticed when taking the battery tray off is that my car is fitted with a fuel tank vent valve, which is wired into the fuel pump electrical feed (and thus energised when the pump is running). You can see it on the far right of the photo above, bolted onto the panel above the wheel arch. The pipe that comes out of this valve was previously coiled up under the battery tray and thus venting into the boot and not out of the car - could this be the culprit?

Any other ideas are most welcome - it's an infuriating issue as the car is pretty much undrivable in the hot weather - and obviously I don't want fuel vapour escaping into the cabin, or anywhere near a source of ignition.

Many thanks

[SimonR]

I think I may have found the solution on the Jag-Lover's forum, so I'll cross-post it here in case it helps anyone.

What I'd not realised when I posted my initial message above was that the smell became really strong just after I had to make a right-hand turn onto the A14. I cleared the first carriageway to the central reservation and then when a big enough gap appeared, accelerated briskly to 70 mph from a standing start, and also turned slightly right as I took off.

Searching on the Jag Lover's forum revealed other people who found a strong fuel smell whilst performing a sharp right hand turn and also taking off suddenly. It appears that fuel sloshes up the filler neck and ends up either coming past the fuel filler cap (if you've got an aged seal, as I have on my car) or worse, gets past the rubber O-ring that seals the filler tube to the tank spout.

I'll put the battery tray and bits back together on my car asap and investigate the fuel filler neck as my next job.

I shall report back with more news when there is some.

[andypryce]

Interesting. Does seem odd though that a vent pipe would not vent to the outside of the car?

[SimonR]

Hi Andy,

It's strange that there isn't more information about the fuel system online, however, I think the issue is that most of the XJ-S chat on Jag-lovers is from US owners and the US cars have different fuel systems.

From a bit of reading online I think that that vent valve actually allows air into the tank to equalise the pressure as fuel is burnt so actually it doesn't matter that the pipe is open in the boot. Certainly the end of the pipe didn't smell of fuel.

I'll report back when I've got the car back together and been able to investigate the situation with the fuel filler.

[SimonR]

I had time to put the battery tray back together this afternoon and have a bit of a look at the fuel filler area, from both outside and inside the car. Hopefully I've fixed the problem.

Somehow, fuel was getting out of the fuel filler, past the cap and into the boot. Investigation revealed that the cap itself wasn't making a particularly good seal, so the first thing I did was to remove the metal plate from the inner part of the cap and bend the lugs backwards a bit to increase clamping pressure when it is turned on to close the tank.



The gaiter that connects the outer filler tube to the filler neck on the tank itself was in good condition and fuel-tight, but I cinched the Jubilee clips up slightly just to make sure. I also checked that the drain pipe that carries spilt fuel from the filler pocket vents to the floor and doesn't leak into the boot anywhere. Therefore, the only other place where fuel could be getting into the boot was the rubber seal that pushes over the outer filler and is clamped onto the car's bodywork by a metal ring which, in turn, is held in place by three screws.

The one on my car was intact, but there was a gap between it and the filler neck and it's entirely possible that fuel could get get past it and drip into the corner of the boot. I'll buy a replacement one if I need to, however, I'm hoping a pair of cable ties will close any gaps, should fuel be able to get past the cap.



I've trimmed off the ends of the cable ties - let's see if this solves the problem!

[andypryce]

I am guessing that if that was the cause it would be worse when tank is full and the fuel is able to escape by that route?

[SimonR]

You are probably right - but at the moment I daren't fill the tank in case fuel prices drop suddenly, so I can't test that!!

The car is being used sparingly this summer and at the end of it I'll empty the tank, so I can replace all the fuel pipes and also refurbish the IRS.

I live in hope that Esso Synergy E5 will be less than £2.10 a litre soon - who knew that the 3.6 AJ6 can easily achieve 34mpg if driven carefully

[SimonR]

Hurrah - I'm pleased to report that this issue appears to be solved. I've taken the car out a couple of times since, stuck a load more fuel into it and driven it in a spirited manner, not a hint of fuel smell.

The cabin smells different now as well, the solvent smell that I thought was left over from the waxoyling that I had done has diminished considerably and seems better every time I get in the car. I guess the smell of spilled fuel in the boot will take a while to disappear completely, but the hot weather will definitely help.

[andypryce]

Good result and worth a write up for the magazine I think.

[davidr]

Good result and worth a write up for the magazine I think.

I agree! Yes please!

[SimonR]

I just emailed you a word doc and some photos, David

[PJAB]

I think that I am about to start a similar journey - I remember reading the great article in the JEC magazine not so long ago about this - so it will help me look at some obvious candidates to see if they are the culprit - but I might start at the fuel filler cap rather than digging into the boot area any more.

I’ll keep you posted if I may - given my inexperience at car mechanical work and low level of knowledge - I find it really helpful to share the problems that I am trying to solve along with what I am up to so that I can benefit from some peer group review time!

Peter