Hi everyone,
The previous owner of my 1984 Jaguar Sovereign, 4.2, decided that one fuel tank was enough for his short runs. He was worried about leaving fuel in a tank which would not be used. Okay, I understand (although one could have regularly switched the tanks over during the drives). However, he did not just disconnect the left tank (apparently the right one was in a better condition), he also removed all the change over valves, fuel feed and return. I cannot see the electrical connections, so these may have also been cut back. His advice to me as I discussed it with him, refuel more often is better than trying to reinstate the fuel system. Your thoughts?
2 is wayyyyy better than one. Worth it
Yeah, thatās what my emotion is telling me. But logic says otherwiseā¦
Put up a picture of the wiring around the fuel pump. All you need is a single wire that has power when the right tank is selected. For some reason most previous owners were idiots at some point. One of mine drilled through the valves and the shavings were everywhere.
Driving around with 300km of range and no reserve and a fuel system that is not fully functional is annoying. I have driven on one tank and on both cars itās been a relief to put the second tank back into action.
Of course if the tank is in bad condition then logic says to leave it.
**
No chance he kept the parts, Kit - and is the āleftā tank still in placeā¦?
Two points; apart from the increased range, it is nice to have a reserve tank - and with two operational tanks, you can, as now, drive on one if the other is out of commission.
The changeover operates the petrol gauge, on a separate circuit - and changeover/return valves electrically. The function of the changeover valve is to open respective tanks to the fuel pump - the return valves blocks fuel returning to the non-selected tank - all three are necessary for using two tanks.
Having the parts, rewiring the electric connections are simple enough, but If you can live with one tank so be itā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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Another choice is to use both tanks but tie them together with a āteeā which effectively turns two tanks into one. Itās not an unusual alternative. Over the years a few posters have done so. In fact, I did so myself on a temporary basis.
The worry is that, if the car is on an unlevel surface, fuel from the high side tank will flow into the low side tank, overflowing it.
Cheers
DD
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Hi Doug, interesting idea, I tend towards trying to restore it to how it should be, but that would certainly be a quick way forward.
Hi Frank,
Thanks for the feedback. Unfortunately I do not have any parts, I think that the guy between me and the seller kept anything that wasnāt bolted into the car! But the more I drive around, the more I think that a second tank would be the way forward. I mean, Jaguar didnāt install two tanks for the fun of it!
Kit.
I havenāt opened the tank yet, it certainly seems (from the filler) that it is not as good as the right (passenger side) tank. But a reasonable used tank here would be around 120 Euros, including the sender. So that would not be too bad. I would still need the change over valves of course.
Kit.
Add two one way valves and resolve that side slope issue
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As i recall, it is 12 gallons each. So, at the cars average MPG,
most buyers would not find that acceptable. OTH, at 24 it is a market plus.
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Will also solve the filing up process, because with just a T the tank will slowly drain as you fill it up.
I agree.
Even though itās a complicated system, and gave me a lot of grief until I sorted it out, itās a unique feature of these cars and has itās advantages.
Mind you, the change over valve is not that great design and might cross leak even when new.
If you are going to reinstate the system from scratch there are alternatives.
One is a Pollak fuel valve and you get away with just one valve as it handles also the returns.
Another is a three port motorized valve and you keep the original return valves, or you change them as well with two port valves. Keep in mind that the Right is NO and the Left NC.
I have a new changeover valve and it is absolutely air tight, I have also dismantled the old valve (the one that was full of swarf) and didnāt see any bad design flaws. After two pump failures I went with two pumps and a relay though, which also worked so well that I never got to make it look nice. One way valves into a T only may work or not. Owerflowing on a slope may be a problem but I doubt that situation happens often? Wouldnāt do it either way.
I like the valves and surely someone can get them off a donor car for you.
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This is a very good solution indeed, and you donāt even need the change over valve.
The pumps have built in check valves so no cross leak or overflow on a slope.
And if one pump goes you have a back-up, big plus.
Thanks David, I think that the parts shouldnāt be too expensive, I would prefer (where possible) to use new or refurbished parts for areas like the fuesl and engine control systems. I have seen that there are a few alternatives. And having driven the Jag this weeks to work and back a couple of times, the extra tank is definately going to come in handy!
Kit.
Thanks for the details and a great technical solution - better than the original! 
Sure. Would I do it again, no. Iād use all original parts this time, and that means used if possible.
However my SI has the two pumps (Which gave me the initial idea of using two pumps) and that is all original so Iām happy nowā¦
If going with two pumps the return valves are still required, and one bracket for the extra pump.
**
You still need functioning return valves, Kit - the pressure regulator feeds fuel back through a single line that āTā through to each tank. Without the blocking of the appropriate return; fuel will feed back to both tanks with either pump workingā¦
Ie, the fuel feed and the fuel return are two separate circuitsā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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So a quick status update.
My friend and I gave the fuel system a thorough check last week and found that the previous owner had removed the parts (change over valves and some pipework) but all electrical cables remain in place, neatly stowed away. Some of the fuel hoses and pipes have been removed, but most have simply been blocked of with a metal rod and a clamp to prevent any leaks. After complete testing that power was being switched to the various cables, I placed an order with Limora (a great resource here in Germany) for the parts; including fuel switchover valve, left and right return line cutoffs, the missing fuel hoses and various clamps and metal fuel pipes. All arrived today.
I managed to get a clean second hand tank, with sender for a good price. So, some weekend in the the middle of july, we will replace the tank and fit all the parts. The aim being to restore the complete original, two tank fuel system. I will post the results when we are finished. Thanks for all the advice so far and wish me luck!
Kit.
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Iām surprised!
Happy youāre putting it back correctly. Good luck! Changing a tank is some work but it is worth the effort.
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