87 series 3 tank vent pipes

(Roger Coole) #1

The vent pipes that run from inside the trunk/boot to the under side of the car are clogged. I tried running a wire down the left side pipe with no luck. I’m assuming the right side is clogged also.

Might anyone know the best way to replace these?


p.s. I don’t have access to a lift, just a floor jack.

(Frank Andersen) #2

Is that the tank venting or the filler lid, Roger…?

If the former; there is some urgency to remedial actions - if they are indeed clogged; the tanks will implode, unless driving with the filler lids ajar…

However, only the ‘European’ versiond use direct tank venting to the ground. In ‘US’ versions, with closed tank ventilation, the tanks are vented through fuel separators in the C-pillars…

What are the symptoms that made you suspect clogged tank vents…?

xj6 85 Sov Europe (UK/NZ)

(Roger Coole) #3


It’s the tank venting. The pipes from the separator to underneath the car. In the diagram labeled CAC2477 and CAC2478 for right and left respectively.

I discovered this when opening the fuel filler caps. Was a loud ‘woosh’ and I heard the tank(left side) pop back into shape. Was also a lesser woosh from the right tank, but no popping.

I found the pipe from the canister to the right rear wheel well was also clogged and have replaced it. I’m thinking I started at the wrong end. I won’t be surprised if I find pipe CAC2479 clogged also.

I know I could make this all go away by just drilling a tiny hole in the filler lid seal, but really shouldn’t. Maybe I should try the European method instead.


87 XJ6


(Doug Dwyer) #4

Probably not feasible. Not at least, without a high level of dedication.

As I recall (I’m on my first cuppa coffee) the pipe(s) you’re thinking about replacing are situated underneath the large over-axle insulting panel, item #1 in this illustration


To remove the panel in one piece means removing the rear suspension. Even then, ‘one piece’ is a bit of a dream because the panel crumbles apart if you so much as look at it angrily.

You might be able to cut away enough of the panel to expose the pipes and then patch the crumbly remains back together… somehow.

One alternative might be to abandon that section of plumbing entirely and replace it with rubber hose, cleverly re-routed and secured. Should be doable with a bit of mulling and effort.


(Doug Dwyer) #5

Which is oft-mentioned but not documented in any Jaguar literature that I’ve ever seen.

Presumably a hose is attached to the small nipple at the filler neck and is routed downward alongside the front of the gas tanks. Access to this area for re-plumbing might be difficult. A ‘fish line’ technique of pulling the new vent hoses into position might be workable.

You might be to disconnect the existing hoses (C38511 in your diagram) from the vapor condensers in the roof pillars, lengthen them somehow, and divine a way to route them outside the body


(Roger Coole) #6

I was afraid it might be something like that. Sounds like they built the car around the pipes. lol

Hard part would be to run the rubber hose out of the trunk/boot. Something to think about.


(Frank Andersen) #7

The tank popping is certainly a sure sign of excessive vacuum, Roger - and impaired venting. Right call…

It’s very unusual for the vent lines themselves to clog - let alone both of them. Restrictors are placed in the lines near the C-pillar separators - which may simulate clogging?

The usual suspects are the pressure relief valve, and solidified charcoal in the canister may block air venting - have you checked these suspects? Bypassing the relief valve, or disconnecting the relevant vacuum hose on the canister is one way of testing?

The two tanks commute via the fuel separators, equalising tank vacuums. So the first tank to be open ‘whoosh’, the next one not - depending on the interval between openings…

As an aside; the amount of ‘whoosh’ relates to the tank levels - the lower the fuel level the more air must enter the tank. Apart from the vacuum level of course - which, with the system working properly, is around 1,5 psi. So a certain amount of ‘whoosh’ is to be expected after driving…

xj6 85 Soc Europe (UK/NZ)

(David Jauch) #8

how about routing them together with the return flow tubes? If accessible… there is lots of drain tube from the large panel that sits under the board under the windshield.

(Roger Coole) #9


I had disconnected the pipe running from the canister to the rear wheel well at both ends and tried to blow air thru it but couldn’t. I’ve also disconnected the pipe from the left separator that runs under the car but couldn’t get any air thru that pipe either. The other end was still disconnected. I’ll have to see if the separators are clear next and if so, try to run a pipe from them down thru the trunk and out the back. Seems to be the only feasible solution.


(Frank Andersen) #10

I ‘think’, in this most unusual situation, Roger - the separators are more easily accessed for further testing of the venting…

You have checked at the pressure relief valve as well? And, have you tried sucking as an alternative? :slight_smile:

I further ‘think’ that it may be worth while to invest in a vac generator - though in principle the re should not be much resistance in the vent lines. However, the necessary air flow though the vent lines is very small - only replacing the volume of petrol used. Restrictors are placed in the vent lines for this reason - and may test your lung power and perception…?

But the ‘groaning’ tanks imply that the venting is indeed not functioning…

xj6 85 Sov Europe (UK/NZ)

(Aristides Balanos) #11

I had tried to blow through my vent tubes and also thought that they were blocked…
But then I tried with my air compressor and air was passing through.

I didn’t know that Frank, it now makes sense that I could blow onnly with the air compressor.