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The Twin Fuel Tanks

The Twin Fuel Tanks

Jan Wikstrom, Jacques Watson, David Litchfield, Anders Backlund

Yelena wrote:

Could anybody enlighten me on the reason for the twin fuel tanks on the XJ6?

*probably* simply that the car is so low and sleek that once you've put the spare wheel under the boot (it won't fit in a wing), there's no room for a decent long-range fuel tank under there -- and the space in the wings is going begging.

Why are the tanks separate and switched? Well, it's handy to have a spare, and refilling communicating tanks would be a real problem -- it takes for ever to fill from one hole, and if you move across to the other hole, you'll find that the first tank is less than full after you're finished with the second.

Most important from the Jag-lovers' viewpoint is the fact that it adds to the mystique -- "it's different, therefore better"... :3+)

If one fuel pump fails you have another one to switch to (in the SII that is). This has saved me many a time. Those darned fuel pumps are very temperamental. The one on my left tank needed to be serviced twice in the last 30 000 km and the right one is stil fine.

Of course, there is another nifty use for the two fuel tanks: You can run the one dry, about 50 miles from the nearest town. Scares the shit out of your passengers.

Two brothers I know share a SIII XJS. Each has their own personal fuel tank so there are no arguments about who last filled the tank etc.

Just a thought regarding the twin tanks...

My sister, who is a steermate (is that the correct word?, 2nd of captain anyway) in the Swedish mercant fleet told me that it was very common on ships to have high/deep but narrow tanks. This was a way to reduce the open surface of the fluid. According to her moveable surface of the fluid is a main problem in acheiving stability ob ships, e.g. tankers but also ro-ro's.

She then forced me to take a flat plate, poured water on it and made me hold it... try that one out! Now consider if you make a flat 24 gallon tank - - even if you would be able to fit it in you XJ - what a large open area.

Some of you might wonder if ca 75 kg's of fuel really could influence the stability of a 1800 kg car. I don't know, but when fluid starts to move strange things do happen. Obviously some 20.000 kg of fluid can influence a 60.000.000 kg ship. So, maybe the peculiar arrangement and geometry of the tanks is a fortunate combination of space available and possibility to reduce fluid movement and hence also avoiding instability. This would also explain why it isn't really necessary from a stability point-of-view to draw fuel from both tanks at the same time.

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