Anybody willing to teach me in plain English, how to use the dual fuel tank system on my '82 XJ6? I understand the obvious, there is a switch on my dash. I read of some talking about a transfer pump. Does it exist and how does it work? If it does exist, isn't a switch for right or left tank rather obsolete? Am i grossly misunderstanding?

 

This first couple paragraphs here might help----

Fuel Tank Switchover Checklist, Series III XJ6

---- if not, post back


Cheers
DD

 

Very helpful, thank you. So, what's this about transfer pump (not from that article, but from another discussion)? Is there such a thing?

 

No transfer pump on your model.

Jaguar used dual tanks on many models in the 60s-70s-80s. Perhaps some of the older cars had a transfer pump...but it doesn't ring any bells with me.

Someone more familiar with the oldies might chime in on that.

Cheers
DD

 

So far my switch seems to work well from left tank to right. My gauge doesn't work though. The guy I bought it from, told me it needed a sending unit. The fact that the gauge doesn't work on either tank leads me to believe it is not likely BOTH sending units.

 

Welllll....maybe not.

The sending units don't have the best reputation. Over the course of 30 years it isn't too far fetched that both have failed....possibly several years apart.

Easy test.....

Remove tailights to gain access to the sending unit wires
Unplug the light green wire
With the key "on" touch the light green wire to ground. The needle should move to "Full".

If the needle swings to full, the gauge/wiring/changeover switch is OK.... and the sending unit is faulty.

If the needle doesn't swing to "Full" then the problem is related to the gauge, wiring, or chageover switch

Cheers
DD

 

AFAIK Jaguars with twin tanks in the rear wings never used a transfer pump. Twin tanks were fitted on the 60s S-Type, the 420, and the XK saloons Series 1, 2 & 3. The Mark VII, VIII, and IX may have had twin tanks, but these are before my time. Cars with carburettors may have had one pump per tank, but no fuel return system as it's not necessary.

 

Any real advantage to having the two tanks isolated and switchable? Why not let them equalize?

 

Some guys DO abandon all the changeover equipment and let the tanks equalize via a common connection---generally a "Y" fitting to replace the chanegover valve.

That's all fine and well if you always park on a absolutley level surface. Think about what happens when one tank is lower than the other. If the tanks are only half full or so, no problem. But if the tanks are nearly full...well...your gas caps better seal perfectly :-)

Cheers
DD

 

good point

 

ok, touched light green wire to ground and my gauge read full so I believe both my sending units are toast

 

New ones here: -

Jaguar Wholesale Parts Dealer | Jaguar Auto Parts

 

I have diagnosed and replaced dozens of fuel tank sender related issues. The most common is not the sender but the plastic floats that fill with fuel and SINK to the bottom.

The plastic floats crack where the retaining ring of metal wire holds them.
I used to replace them with brass floats from some other model car but that was back in the 80s and 90s when I worked on alot of them. I can't remember where I got the replacements from.

The floats are NSS from Jaguar so you will have to replace the sender or find a suitable replacement for the float if it is full of fuel.

bob gauff

 

Very useful post from Bob Gauf. I had forgotten about float leaks. Leaks were once also found with carburetor floats. SU had brass ones soldered together, and it was commonplace to resolder them where a leak was found. Later they went over to plastic which were supposed to be less prone to leaks, but not repairable, of course.

 

Does replacing the fuel sender require dropping the tanks?

 

nope...just requires removing the tail light. BTW, I removed the sending unit to clean my tank and found it was seized with rust. After freeing it up and cleaning a bit, IT WORKS!! HAHA

 

Nope.

Just remove the tail light asemblies and you can reach right in and change the senders. "A walk in the park"

Cheers
DD

 

This particular park is a No Smoking area. Do be careful when removing and replacing these things. Disconnect the battery first so there is no possibility of a stray spark.