1987 Sovereign 3.6 Fuel Tank

(Kevin Thiele) #1

When cleaning out the fuel tank prior to coating with POR-15 sealer, I used an air gun to dry it out but the air gun moved when I was absent and burnt a small 2mm dia hole in the top of a blue plastic tank(??) within the main metal tank. The outlet and return hoses are connected to this blue plastic thing but I can’t see whether it’s actually a tank or just a baffle.

The tank does not have an internal fuel pump, that was on later models. I haven’t been able to find anything on the internet and local Jaguar dealers have been unable to assist. Only the complete tank is shown in the parts catalog with no internals.

Can someone tell me if this is actually a tank and is it pressurized, or is it just merely a baffle?


(Brett) #2

Do you have any pics? I did some work on the tank in my '89 when I rebuilt everything, but I’m not sure if its the same as what your '87 would have.

(Kevin Thiele) #3

Hello Brett

here’s some photos

(Kevin Thiele) #4

The plastic is blue originally, I’ve just applied silver POR-15 sealer.

(Brett) #5

As it was explained to me by the shop I took mine to for cleaning, that is a tank that holds a small amount of fuel as an emergency reserve. Basically, when the gauge says you are completely empty, you still have a small amount of fuel to get you to the nearest station. The shop said there is something similar in a lot of motorcycle tanks. I’m doubtful a hole in it would affect anything unless you ran the tank empty, but I could be wrong.

(Kevin Thiele) #6

Thanks Brett,

It sounds logical so I’ll go with that and reinstall it. But just to be on the safe side because the POR15 coating may not adhere to the plastic, I’ll put an inline filter before the pump that can be easily replaced from the boot (trunk in US).


(Robin O'Connor) #7

Not quite correct, if its the ‘tank’ I’m thinking of the fuel pump sits in there? If so it holds the fuel returned from the injector rail and ensures that the pump does not run ‘dry’ when the level is getting low.

(Kevin Thiele) #8

Hello Robin

The early XJ40’s had an external fuel pump like mine which is attached to the chassis rail. It was internal from about 1990 onwards after they had a bit of makeover.


(Brett) #9

As Ruggers said, these cars definitely have an external fuel pump.

Your explanation of what it does may be accurate though. Again, this is just how it was explained to me, but I have no doubt that its not the easiest thing to explain to someone unless you have to do it all the time.

(Robin O'Connor) #10

Yep should have picked up on that :slight_smile: I had an ‘88 4.0 with the same set up.

(phillip keeter) #11

I would be worried that this burned up plastic, inside of your tank, is going to cause some debris problems in the fuel. This may occur in spite of the sealer application. You may want to fill the tank and drain through a strainer to check it out prior to installation.

(Kevin Thiele) #12

Thanks Phillip

Already done it. But just to be on the safe side, I am putting an inline filter between the tank and fuel pump where it’s easily accessible.

(phillip keeter) #13

Excellent! No better place for one.

(MURRAY ) #14

Unused fuel from the engine returns to this blue tank and is used first to supply back to the engine, when you run out of fuel, this tank is empty as well and you must fill your car with adequate fuel before it will fill this tank and be pumped up to the engine, when cornering hard, this tank allows a constant fuel supply.
Make sure both hoses are connected at the bottom,
Hope this helps.

(John Quilter) #15

And I believe this is why some of these cars can experience a vapor lock and fuel pump cavitation in extremely hot ambient temperatures. The returned fuel from the engine compartment, which is already heated from the lines and fuel rail, then runs in lines near to the hot exhaust system components under the car gaining additional heat. It then dumps into the swirl chamber which then supplies the external fuel pump that cavitates due to the concentration of hot fuel causing the fuel pressure to drop and the engine to stall. Adding some additional cooler fuel to the tank brings down the temperature of the fuel and the car will restart. There is a Jaguar bulletin to address this issue but the modification is complex and parts are no longer supplied. My solution was to insulate all the accessible underfloor exhaust components and add a fuel cooler in the return line. Currently awaiting some really hot (over 95F) weather to verify resolution of this issue.

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(Kevin Thiele) #16

Thanks Murray and John_Quilter. I will install some heatproofing on the fuel lines before I reinstall. I was also told by a mechanic who has restored a couple of the older XJ’s to give the return line a very good cleaning too as it gums up over time without use.

Hopefully I’ll finish the job this weekend and fire it up for the first time in 15-16 years.

Thanks all for your contributions.