Mar 202013

A fuel expansion tank was added during the production run of the Series 2 cars, located in the boot space on the LHS rear wheel arch. The expansion tank is vented to the outside and so it’s internal pressure is always equal to the current atmospheric pressure.

Thermal expansion of the fuel increases the pressure in the fuel tank relative to the pressure in the expansion tank. As a result, fuel passes from the main fuel tank to the expansion tank until the pressures are equalised. As fuel is consumed or when the fuel contracts due to cooling temperatures, the pressure in the fuel tank decreases relative to the expansion tank. Any fuel in the expansion tank is then returned to the fuel tank as the pressures equalise once more.

Note: I have subsequently seen a Jaguar Service bulletin which indicated that fuel passes back from the expansion tank to the fuel tank by gravity, not pressure. Although with such a small bore for the breather pipes, I would have thought it’s probably a combination of gravity and pressure to overcome airlocks.

When the expansion tank was removed, I carefully labelled the various pipes between the two tanks with masking tape. For some reason I wrote the descriptions on the masking tape in pencil, which didn’t stand the test of time and were illegible by the time it was ready to be refitted. A lesson learnt!

A piece of 6mm jute was bonded to the tank as a protective layer between the tank and the wheel arch. However the bond was greater than the strength of the jute and so would need replacing. It’s available from most of the re-trimming firms and was bonded using the same AF178 contact adhesive used for the heat insulation.

I now had to work out how to make the connections between the two tanks as it’s not covered in any of the manuals available. The expansion tank has four outlets and the fuel tank only three. The additional outlet on the expansion tank is for the vent which exits to the outside via the boot drainage pipes. Although I believe the vent is connected to the emission control system for cars supplied to the USA.

The first task was to work out the difference between the four internal pipes in the expansion tank. I used a length of garden wire with the end bent over to form a hook. This enabled the wire to be jiggled so that the hook engaged with the end of the pipe inside the tank and therefore could determine the internal length of the pipe.

Three of the pipes ran from the bottom to the full height of the tank while the fourth terminated as soon as it entered the tank, as depicted in the photo. The short red pipe (A) is at the bottom of the expansion tank and therefore must be for returning fuel to the main fuel tank. So I would expect this to be connected to a pipe which terminates fairly high up at the top of the fuel tank.

The other two blue pipes (B and C) terminate at the top of the expansion tank and so would be for the pipes passing fuel from the main tank to the expansion tank, when the main tank is full to the brim. The fuel entering the expansion tank via B & C would then fall to the bottom, to be returned via pipe A when the pressure in fuel tank reduced.

I would therefore expect B & C to be connected to pipes which would normally only be submerged in fuel when the tank is full, ie terminating at the very top of the fuel tank. It was now time to get the USB borescope out to investigate the fuel tank as ends of the pipes are hidden due to the internal baffles.

In fact the corresponding red pipe A in the fuel tank was easy to determine as the end of the pipe end can be felt via the large oval opening. The borescope did confirm that the other two pipes terminated at the top of the tank. The end of pipe A turns downwards for about an inch. I assumed two pipes are needed to pass fuel to the expansion tank due to the baffles. It shouldn’t matter how the B & C outlets are connected, ie B to B or B to C, as they are both performing the same role.

Anyway, assuming my logic is correct, I think I’ve worked out the correct connections!!

 Posted by at 10:35 am