[xj] Equalizing gas tanks: the saga continues

I have been experiencing the dreaded XJ equalizing fuel tanks for some time
now, and so far have had no success in repairing it. The fuel switchover
valve and the fuel return valves appear to be functioning normally, and my
mechanic has made an expensive hobby out of explorative surgery. I have
also dumped much techron in the tanks in the hope that it will dislodge any
sticking valves. So far, no change.

My question is this: does it matter that the damn tanks are equalizing? I
don’t really care about the equalizing problem per se, but am just concerned
because if one ignores minor problems with these Cats, some other system in
the car usually takes revenge later.**********************************************************************
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(V1.5)

Hi Jonathan, I happened to see your post. Lately I’ve been deleting most of
them because most lately seem to have nothing to do with keeping our Jags
running in top condition. Anyway, if your tanks are equalizing, and fuel is
returning to the proper tank, the problem is the changeover valve in the
boot. I really don’t think any amount of Techron or anything else you can
pour in there will help. As a matter of fact, after pouring a fuel system
cleaner in mine, my changeover valve in the boot and my non-return valve both
failed while that was in the tanks, resulting in the cars inability to hold
fuel pressure when shut down and equalizing of the tanks. Maybe it was
related and maybe not. The changeover valve is not that hard to replace.
The main thing is to devise a means to clamp off the lines coming from the
tanks during replacement (or drain them first) or they will empty into the
boot when you take them loose. Also you might want to put as many towel or
rags as you can under there as some fuel spillage is inevitable. I hope this
helps.

Steve R
85XJ6

easy fix…install a T fitting out of the fuel pump in the trunk. both tanks
will equalize as if u had 1 big tank (law of physics) no more probs. a fix
at 8$

By the way, anyone know why Jag created the switchable (as opposed to
equalized) tanks in the 1st place?

Alex
79xj6

DPritch901@aol.com wrote:>

easy fix…install a T fitting out of the fuel pump in the trunk. both tanks
will equalize as if u had 1 big tank (law of physics) no more probs. a fix
at 8$

At 10:54 AM 9/27/99 EDT, you wrote:

easy fix…install a T fitting out of the fuel pump in the trunk. both
tanks
will equalize as if u had 1 big tank (law of physics) no more probs. a
fix
at 8$

Do you mean on input to the fuel pump? I have a boat with two tanks which
feed to a tee just before the filter and pump. The law of physics says
liquids will seek their own level. They do. I have not seriously
investigated the fuel switching system on the XJ6, as mine works properly
(for now), but it seems that the same setup (a tee properly placed) would
work. No matter where the fuel returns, both tanks would be at the same
level, Have you (or anybody) done this? It seems it would eliminate the
switch and a lot of solenoids(and problems). only one gauge is needed (my
boat has a gauge only in one tank since they are equal). Any problems with
this theory? What is the purpose of this whole switching system anyway?

Mike
87 VDP>

I suspect that they put the switching system in to compensate for leaky
gas tanks. I mean, if you have a tank that’s leaking, wouldn’t you like
to run it dry as soon as possible, then block it off from the rest of the
system?

I’ve wondered about this too. My SWAGs are

  1. They wanted to get as close as possible to a 50/50 weight ratio as
    possible. This would align with the performance oriented nature of the
    Series 1 (i.e. IRS design, etc). To compensate for the weight of XK engine
    they moved the weight of the fuel as far behind the rear axle as possible.
  2. They wanted to keep the trunk volume acceptable. This is a
    challenge given the beautiful sloping of the rear area.

Assuming that these were two design objectives, the current layout makes
sense. The saddle tanks move the weight behind the rear axle, the spare
tire helps out here as well and the free area immediately behind the rear
seat available for trunk space.

The best explanation I’ve heard for the switch over system between the tanks
is that if the tanks are full and the car is parked laterally on a steep
grade then the fuel from the “upper” tank will drain out of the filler neck
of the “lower” tank. If you’ve ever seen the parking in parts of San
Francisco, you’ll know this is a real concern.

This guess at rationalizing the design is worth exactly what you paid for
it. :slight_smile:

cheers,
Rick-----Original Message-----
From: Commander Spectre [mailto:spectre@fok.com]
Sent: Monday, September 27, 1999 11:24 AM
To: DPritch901@aol.com; JJEngler@hhlaw.com; XJ List
Subject: Re: [xj] Equalizing gas tanks: the saga continues

I suspect that they put the switching system in to compensate for leaky
gas tanks. I mean, if you have a tank that’s leaking, wouldn’t you like
to run it dry as soon as possible, then block it off from the rest of the
system?

Perhaps the idea was to keep the fuel from shifting during cornering. In a
boat, the tilt of the boat keeps the forces on the fuel pretty much
perpendicular to the lay of the line between the tanks, but in a car, the
centrifugal force would tend to make the fuel shift to the tank on the
outside of the turn.

I would think the amount that shifted would be small given the diameter of
the tube, but on one of those 270� freeway ramps, at a good speed, you might
transfer half a gallon of fuel. Would it affect handling? I guess if you
were driving the car right on the edge, it would.

The only other advantage, besides the suggestion that you could bypass a
leak on one tank or side of the system, would be that you could compensate
for certain variables in operation. For example, because usually the driver
(U.S.) is heavier than the passenger, if there even is a passenger, I draw
from the left tank first, which balances the car. Then I draw from the
right. Does that affect handling? Darned if I know – I’ve never pushed the
car that hard, and I think you’d be skating right on the edge if whatever a
tank of fuel weighs throws you over!

“Mark 1” Mark Stephenson
1958 3.4 Litre Saloon
1984 XJ6 4.2L
1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) Concours, Oct. 9
Web site: www.cableone.net/jcca/con99/con99.htm----- Original Message -----
From: Cannara cannara@ibm.net
Cc: xj@jag-lovers.org
Sent: Monday, September 27, 1999 10:00 AM
Subject: Re: [xj] Equalizing gas tanks: the saga continues

By the way, anyone know why Jag created the switchable (as opposed to
equalized) tanks in the 1st place?

Alex
79xj6

DPritch901@aol.com wrote:

easy fix…install a T fitting out of the fuel pump in the trunk. both
tanks

will equalize as if u had 1 big tank (law of physics) no more probs.
a fix

at 8$

no problems,i did it 3 days ago working fine…wanted over 300$ ro
replace all 3 valves said i had rust in the fuel tanks and clogged up all 3
valves, maybe soooo don cleveland ohio

I really like having two independent gas tanks on the Jag. When they
are working properly, I run on the first tank down to one quarter full,
then switch to the second tank and see how many miles I can squeeze out
of it. When the second tank runs dry, I switch back to the first tank
and start looking for a gas station. Cheap thrills.
Regards, Billy
86XJ6 S3 Daily Driver

u run it dry??? suck up rust and water in to the system???