XJ Fuel Tank Management Replacement Kits

Hi all - first post in this XJ section of the forum.

I normally live in the Etype section as I have a Series 3 Etype.

I am in the process of acquiring a 76 XJ12C and one of my concerns is the tank management system. I know how it it works and how well it works but can play up occasionally. What is feeding my concern is that I bought a burnt XJC 30 years ago and it was burnt because the fuel system in the boot played up, caught fire and burnt out the car.

The other problem is that our fuel hoses at most service stations in Australia are now too short to stretch across the boot to fill the outside tank.

So a question for a newby - are there any kits or known modifications that allow both tanks to be filled from one filler and the engine can run from the tanks without the risk of the return overfilling a tank in case of a valve failure.

Thanks

Garry

I can only imagine that if you want to eliminate the problem of drawing from one tank, while returning fuel to the the other tank, you will end up also eliminating the reason both tanks were originally managed the way they were. The alleged original design was to keep fuel from overflow spillage from the ‘downhill’ tank if the car was parked or run on significantly angled terrain. You can easily change the system by eliminating the main fuel tank solenoid valve in bottom of the boot. Just put a ‘T’ in place, and you will then be drawing from both tanks all the time, and it won’t matter which tank gets selected for the return feed, as it is going to self level the fuel in both tanks through the ‘T’. There really isn’t a solution to being able to quickly fill BOTH tanks from only one filler port, as the filling station pump will fill the tank(s) faster than the fuel can passively run through the ‘T’ to the other tank.

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First order of business would be to change ALL hoses with Gates Barricade Low Permutation, or equivalent marine grade fuel hoses.
Also check the condition of the tanks, remove the in-tank filters and add High Flow filters before the pump, easily serviceable.
Tons of info in the archives.

Hey, welcome! I fill both mine at the one bowser in multiple Sydney stations. I use an old hoodie under the delivery hose to keep it off the paint. The new spool type bowsers, admittedly, are not so easy.

It strikes me as very poor design if a fuel pump designer has made the fuel hose just too short to fill on the other side of the car, otherwise fuel station capacity (and turnover) is substantially reduced! The XJ after all has one of the shorter hose reaches required. In my brief career encounter with forecourt design this was always a key design criteria. Find a fuel station with longer hoses!

Though as I type I recall a pic of a Mk X parked smack in the middle of 2 pumps, with one nozzle in from each side, filing both tanks at same time.

In general terms the XJ design with tanks / hoses / pumps in the trunk (and connections doubled up because there are 2 tanks) is more vulnerable to issues. But hose replacement and careful maintenance should crack it.

Having said that I did get a call from my Jag specialist a few years back who broke it to me that there had been ‘a small explosion and fire in the boot of your car sir’. Mechanic had been working on fuel system with enough free fuel and vapour that when he accidentally earthed a live wire the spark set off a vapour explosion, rapidly extinguished. They replaced the melted boot carpet and the mechanic had to regrow his apparently singed beard.

So disconnect battery while working in there!

No. At least none that overcome that over-filling one tank issue.

I’m in the process of installing FI in a lumped Series 2 and I noted with interest the original set-up of a simple ‘T’ with the tank cut-offs done via the poppet valve pumps. Not a solenoid in sight.

I recommend looking at the Pollak 6 port electric valve. I am in the process of installing the Pollak and will certainly report back but the guys here who have used it are all very happy with it.

If returns are already in place with old Jag solenoids like in a V12 the change over should be pretty straight forward using the original wiring. It will even switch tanks using the original dash switch.

Thanks for the replies and the observations - much appreciated. If I was in the process of rebuilding a vehicle I could certainly rig up something that would be safe and do what I want.

However I certainly not going to be dismantling things that are currently working OK - but the point is taken about checking all the wiring and plumbing in the boot.

From the responses it would seem that there is no “standard” kit or mod which is what I was most interested in. I think I will just add an item to the service schedule to check condition of plumbing in the boot.

I have another vehicle with fuel fillers on both sides and have to advise the service station attendant that I will have to move the vehicle to fill the other side so they will not get concerned I am doing a drive off.

Here is a pic of the burnt XJC I bought 30 years ago but the body was just too far gone - still got the engine down the backyard.

Thanks

Garry

My Xj12 has a mod to simplify the system- one fuel pump, T ‘s in the fuel pump feed. Works fine

I have had zero problem with accessing both tanks with petrol pumps in Vic and Tas. The transfer is not fast enough for any meaningful amount to move to the other tank in the time it takes to change sides

No over-flows. no issues

I didn’t like not having the twin tank system, and initially planned to change back, but now am happy with the p.o’s work

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Russell, is your car carb or fuel injection? Does it use a fuel return to the tanks? Is the return T’d also?

Mine is carb, there is a return, it has a tee also i reckon

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When I started my delivery trip home all I really knew was drive one tank to new empty and hit the switch to change to the other tank and keep driving and look for a fuel stop. Didn’t quite go to plan as the electrics on a 48yo car can play up and often the gauge did not switch but soon learned that a few hits of the switch would eventual move the gauge to the right tank.

Next issue for me was there was no indication on the switch which tank I was in but soon leant that switch in was left tank and switch out is right tank.

Getting home Ok I read the workshop manual

Says “indication of which tank is being used in daylight is via a white band around the switch when the right tank is selected” - this does not show on my car.

Says “at night, illuminated arrows top and bottom of the switch show which tank is selected” - again does not show on my car.

So do I have a little electrical gremlin with my switch that prevents me from seeing an indication of which tank is being used or does this function outlined in the handbook not actually apply.

In the same general area of the car, the 12v socket, the master central locking and the master electric window switch do not work indicating a fault - hopefully just fuses.

Thanks

Garry

The switch needs repair or replacement.

There are two arrows at face of the switch. If the illumination of the switch does not work they will not show.

[quote=“AussieEtype, post:11, topic:432581, full:true”]
…Didn’t quite go to plan as the electrics on a 48yo car can play up and often the gauge did not switch but soon learned that a few hits of the switch would eventual move the gauge to the right tank.
[[/quote]

The changover switch has two separate functions, Gary - one; it switches the gauge’s connection, ground’ to the respective tank. ‘In’ for ‘left’ and ‘out’ for right - be aware that the gauge is rather sluggish in reacting…

The second function; it connects power, switch ‘out’, to the return and changeover valves - setting them up to the ‘right’ tank. With the switch ‘in’ there is no power through the switch - sort of ‘off’ position.

The white band is of course only visible with the switch ‘out’ - however it’s easier to see/feel if the switch is ‘in’ or ‘out’, than to look for the white band (and works at night, but a light is then better)…:slight_smile:

The most common fault with the switch is that it fails to latch in the ‘in’ position - this can be ‘fixed’ temporarily by jamming it with a thin strip of cardboard. However, as Aristides say, a switch fault require replacing the switch - and/or attending to the lighting.

The two functions are electrically separate and may fail individually - one is detectable by observing the gauge (if fuel levels are different). The other detectable by listening to fuel return at the tanks…

The 12V cigar lighter is fused with some other items - it may blows if the lighter is ‘mishandled’…

Non-working switching is usually with the switches themselves. The windows are fused with thermal fuse - which initially connects - then ‘break’ power with overload, then resets. Central locking may be similarly fused - but also, if you have the solenoid set-up; two relays are involved. So what are the exact symptoms…?

Frank
xj6 85 Sov Europe (UK/NZ)

Thanks for those comments - supports my thoughts on old electrics but I not being familiar with the car I thought I would ask. I have spare switches to check things against.

The symptom with the central locking system is that the switch in the centre console does not work. Maybe electrics again but the car does have a alarm system that does provide alarming, immobilisation and central locking so that may have played up with the wiring to the switch or bypassed it.

Thanks

Garry

My reason for asking was that the early versions of central locking only used the consol switch for lock/unlock, Garry - on later versions the lock/unlock was also operated by the driver’s door key.

One diagnostic technique is to manually lock and unlock the door and then try the switch. There is a possibility that either the lock or unlock function is disabled by other faults than the switch…

As an aside; it’s relatively easy to install remote central locking…

The usual malfunction of switches is burnt/dirty contacts - which may be cleaned. This is pertinent for all switches - though more exotic faults may sit deeper, of course.

Frank
xj6 85 Sov Europe (UK/NZ)

Thanks Frank - currently has remote central locking that works well - just wondering about the central switch.

I think I have a few of those burnt/dirty switch contacts and over time I will get to them.

Cheers and thanks for your input.

Garry

Garry,

as for the fuel selector switch: the white band around the button body often deteriorates over time, as in the course of every in/out or out/in movement the button body grinds along the switch surrounding and the white color gets scraped off.

At night and with the (parking or main) lights on the switches are illuminated either showing the top green or the low red triangle pointing at the respective tank. As a matter of grounds problems of the switches the illumination often gets lost. In this case pry out the clock at the center, then push out the twin switch block (fuel select + heated rear light) from behind, undo all the contacts, clean and grease. Typically, the illumination will be restored. If not, check the bulb at the center of the switch cluster.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

Thanks Jochen - good information and advice - thanks. I will before too long start pulling dash components and following down these little defects.

Garry

As remote is an aftermarket fit, Garry - a PO may deliberately have disabled the central switch…?

Frank
xj6 85 Sov Europe (UK/NZ)

Yes he may have, however the key in the door still activates the central locking.