Messrs - Does anyone have an idea of the size of the fuel pick up pipe that’s in the fuel tanks? This is the line that sits right over the drain plug and onto which the in-tank fuel screen is fitted. I’m asking, because I was hoping to fit a different ‘sock’ over this line, one that I can get locally today and just need to know what size opening to get. Also, has anyone by chance, fitted anything other than the prescribed plastic cylinder fuel screen when cleaning out tanks.
Thank you,
Peter
Peter,
You can omit the screen filters altogether and put inline filters between the tanks and the change-over valve.
The size is 1/2", many to choose from and much more accessible for servicing and cleaning.
Aristides
Peter,
The outer diameter of the fuel tank pickup tube is 1/2". This is the same as the inner diameter of the in tank fuel filter, CBC5649, that fits over that tube.
Attached is a picture of one of the two filters that I have on hand to install in my 1984 XJ6 Vanden Plas. The drain plugs are out, the fuel tanks are empty, and I will be installing the filters this week, along with new fuel drain plug seals after cleaning out some minor debris that was at the bottom of both tanks. BTW, the filters cost me a little over $20 US each. In addition to the in tank fuel filters, I also installed two aftermarket in line fuel filters (circled in red in the second attached picture) between the fuel tanks and the changeover valve to protect the changeover valve and fuel pump from in tank debris.
Paul
Paul
Thank you guys, this is exactly what I was looking for. I notice you both have inline filters, and I will do the same. Also, I notice in Aristides’ picture, the fuel hose that is looped around the pump before connecting to the metal line to the filter is eliminated. This makes sense, as the pump outlet just about faces the metal line, but do you know why that extra length is there in the first place? Seeing how it looks without just makes sense all around.
Thank you, again.
I have wondered also… I guess to eliminate vibrations? Or for ease when changing the fuel pump?
Anyhow I had no ill effects with the short hose and looks much neater.
Aristides
Aristides, Paul - let me ask for your take on the following. Considering all the troubles people have mentioned with tanks, fuel screens, switch over valves and solutions that range from replacement to hitting components with hammers to ‘wake them up’ - could one connect the fuel tanks, much as they are now in the back of the trunk with a large diameter hose, but instead of the switch-over valve just have a T-fitting going to the pump. That way (i’m guessing) regardless of which tank the return valves dump the fuel, the level in both tanks will equalize due to the now direct hose connection between them. And with the T-fitting from this very same hose (1/2") also feeding the the fuel pump. And maybe eliminate the switch over valves in the wheel wells entirely and have the fuel either go to both tanks at once, or find its way to either one to be distributed via that hose that feeds the pump. The only issue, perhaps, may be that the fuel pump would utilize the entire volume of that 1/2" line, but any stop lights or letting off the gas would reduce that consumption and allow fuel to drain from the tank that has more fuel to the other one. The tank filler seals might need a small hole to allow air in to equalize, but most are hardly airtight anyway. Just typing out loud, to see how the current set up could be made less convoluted. Thank you guys, again.
Yes. And somewhere in my bits I have such a T in tin.
There is one peril. but a fix is available. if you park on a down slope, one side of the car higher than the other and have a lot of gas aboard, the up dank will drain to the low tank. If there is not enough spade, an overflow will result. Spilling fuel not a good thing.
As long as the changeover valve works, I’d eave it as is. And if it fails, fix it or replace it.
The two tank fill is apart of Jaguar elegance. Even if a bit of a pain at fill uop time, I kida like do8ing the piroutee…
Carl… f .
Peter,
I couldn’t agree with Carl more on this matter. Search the archives and you will find lots of posts from those proposing to fit a T and bypass the changeover and return solenoid valves.
I like to keep my Jaguars working as originally designed and it would be against my nature to make a bodge like this. When I have encountered problems with the fuel delivery system I identified the failed component, replaced it with a proprely functioning one, and returned the system to it’s original working condition. I know that others have chosen different paths.
I did make one modification to the fuel delivery system to add the inline fuel filters between the fuel tanks and the changeover valve. I experienced some random fuel delivery issues which I attribute to fuel tank debris and several years ago I added an aftermarket fuel filter between each fuel tank and the changeover valve (suggested by former list member Bruce Hugo) in my three Series III saloons. Since then I have not experienced any fuel delivery issues with my two XJ6s (I sold my 1987 XJ6 Vanden Plas in August 2018) or V12 Vanden Plas.
Paul
Peter,
I can’t speak to Aristides picture but when I removed and replaced all of the original fuel hoses in the trunk area I replaced each section of old hose with the same length of new modern equivalent low emissions fuel hose.
I believe that in order to control costs Jaguar did not put any parts on their cars unless they were absolutely necessary. Since I am not a fuel system design engineer I am not certain why that additional length of hose was required, but I had plenty of fuel injection hose on hand and it was quick and easy for me to just replace that original hose with a modern fuel injection hose of the same length.
BTW, I suspect that the additional hose length is there to dampen fuel pressure variations to protect the fuel system components, but I have nothing to back up that suspicion.
Paul
Understood and appreciated, Paul. But consider the actual “original” design, as introduced on the Mark X, and continued through the 420G and Series 1 XJ6.
These carbureted saloons had twin tanks, each with its own low pressure SU fuel pump. The pumps were "Y"ed into a single line to the carbs. The changeover switch selected which pump to power, and which fuel level sender to connect to the fuel level gauge. There were no relays, and no changeover valve was needed because each pump contained an internal one-way valve, preventing fuel flow into the tank. Those of who own these model appreciate the redundancy–a failed fuel pump, tank sediment, tank water etc. could be temporarily remedied by switching to the other tank.
This design was first modified when the charcoal canister fuel vapour system was added, and vented tank caps were eliminated. A failure of this system could cause vacuum to appear in both tanks–the car would die on the road, and switching tanks didn’t help.
The next mod was FI. This required circulating fuel, and a high pressure pump. The Bosch pump chosen by Jaguar (already used on Alfas) was of a design that lacked one way valves. Jaguar chose to keep the switchable tank design, so a changeover valve became necessary. And another similar valve had to deal with the recirculation. But for some reason, only a single pump was fitted, so that redundancy was lost at the same time complexity was added.
It’s not clear to me why Jaguar didn’t scrap the switchable tank idea altogether, but there are many similar examples where old designs carry forward. For example, the exact fuel cooler used on carbed cars with AC to protect against vapour lock was retained on FI cars–but its function was to cool petrol returning to the tanks. Odd that the same device could be optimal for both uses. Or did Jaguar just keep kludging along as needed, perhaps because their relatively low production volume didn’t allow “original” designs for each new model year. IMHO.
Indeed, Robert, that might be it.
A friend has a TR5 PI. It seems that fuel injection technology was not as explored in the days as he told me that there was a notorious source of failure as the fuel lines were pretty close to the exhaust. As long as the tank was full and the car was driven hard (high fuel consumption) there was little unused petrol and even though heated up during its return trip it had a chance to be cooled down again in the tank. Once the fuel consumption was lower (e.g. stop-and-go traffic) and the tank got closer to empty the fuel would get hotter on every cycle until the some part in the system wouldn’t tolerate this any more - at least that’s how I remember it. So, maybe Jaguar found it a good idea to cool down the fuel even for its way back to the tank …
Enjoy the weekend - I had my first run in the XJ after like eight weeks, but it started on its own battery!
Jochen
75 XJ6L 4.2 auto (UK spec)
Ja bestimmt, Jochen. Jaguar (and others) recognized that cooling fuel returning to the tank was a good idea in hot weather. They even wired the AC on XJS dropheads so that the compressor was switched on for fuel cooling even if the hood was down and AC not in use.
But I was referring to Jaguar’s continued use of the exact heat exchanger that had been designed for the far lower rate of fuel flow into carbs, as compared to the much higher rate of continuous fuel flow back into the tanks. You would think that the optimal designs for the two uses would differ. But Jaguar retained the old part, and with the same configuration.
Indeed, another example of what I was talking about–Jaguar kludging old designs rather than substituting new ones–is this configuration. Before fuel cooling to carbs was fitted, the AC compressor was on the exhaust side (not great) and the suction line ran directly to it from the evaporator outlet, whose hose fitting passed through the bulkhead right behind the compressor. This was a straight shot, parallel to the engine. But when fuel cooling was introduced, the suction line was passed over the hot engine to the heat exchanger near the carbs, then back over the engine again back to where it came from.
I doubt if this arrangement would have come from a drawing board. If it did, it would have been a good excuse to move the compressor to the intake side, away from exhaust heat. Rather, it’s an example of evolution from an earlier design. BTW, this is claimed also for the similarly circuitous path of a nerve that goes from brain, down near the heart, then back up to the voice box.
Great that your driving your Series 2! Our winter here in Missouri hasn’t permitted that unless I want to add to the rust. 
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A petrol tank must be somewhere, Bob - and with lots of empty space in the wings why not there instead of encroaching on boot space. Which of course meant two tanks - and making it possible to switch between tanks seemed a good idea (and still does)…
On the xj40 a single tank was fitted for safety reasons (ref Nader) - with predictable results…
Frank
xj6 85 Sov Europe (UK/NZ)
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Are we forgetting the earlier big saloons? My MkIX had twin fillers/twin tanks and I believe twin pumps. The MkVII and VIII were presumably the same, which puts the design back to the late forties.
The D had one tank and twin pumps but that wasn’t for redundancy as they both ran full time. Having a fuel take-off at each side of a single tank was to avoid fuel starvation with low fuel level during long sweeping bends.
Sure, Robert,
maybe they found the old system over-engineered and sufficient to cater well for the new one, even while it demanded higher capacity, or it was just “let’s see how far we’ll get”.
Talking in terms of training of workshop staff, but also of spare parts support every argument is pro continuity, even though continuity sometimes may not yield the optimal result. It may be an urban myth, but it is nicely told, so I repeat it - early in the 20th century it was discovered that the QWERTY keyboard was far from optimal for typing English texts, but nevertheless it survived until today, because it was never possible to either change all keyboards (aka as typewriters) or typing staff simulaneously …
What is more - AC was always suspect to European car engineers. Even in the late 1970s Volkswagen engineers found AC definitely nonsensical for the Golf Mk II and designed it only in response to the demand of US consumers. So, even for a luxury sport sedan as the XJ I doubt that the engineers started with the AC system. In fact, the heating and ventilation became the most significant, basically the only, technical change from SI to SII, aside from the different layout of the wiring loom.
Today I had the XJ in the air as it started to leak more oil than I find tolerable. Before that I even found the brake fluid reservoir spilling over - possibly boiling brake fluid caused by a seized caliper. I cleaned up everything (luckily no spillover on the paint), took out some fluid and intentionally operated the brakes on the return trip. Hopefully, the caliper worked loose. At least the car wouldn’t pull sideways, and brake effectiveness is as it should be. Unfortunately, I still have no clue about the oil leak - wiped everything off and am going to take a longer trip next week to find out what happens.
BTW, this morning, on my way to the usual grocery shopping an Alfa 1900 Zagato came my way - weather was fine and no salt left on the roads - twin cams saluting - even though his were 20 years older than mine
Enjoy the week end
Jochen
75 XJ6L 4.2 auto (UK spec)
QWERTY!!! Thanks, Jochen. Never knew that ! I have been aware of it as a quick reference to key lay out. My ancient pocket PC used it. Dell AXIM. Now near useless. Will no longer sync to one of my old Dells on XP!!
Sad, it was far more sophisticated than I. But, I used it a lt anyway…
So, which language fits QWERTY better? Might I guess., German?
Back on point.,
Yuk, that idiot Nader, again!!! Tank location safer from collision, but when it reached, oh boy, closer to the occupants!!! Never mind that the twi8n tank configuration cut the exposed fuel load in 1/2.
I think the Jaguar system was purely evolutionary, as opposed to redesign for each model. Wheel reinvention??
The fuel cooler is interesting. The LT1 in my 83 lives just fine without it. And, I kept the entire Jaguar fuel system. Why change? It works just fine.
As to one exposed pump to replace two submerged ones? Could it be that, ease of service.
And, aye, boot space is not all that much. So, use of the space in the wings seems logical. Plus, a plus in weight distribution of a nose heavy car…
The use of fuel injection hose whether needed or not seems a reasonable thing.
I like the prepump filter idea. But, so far, fuel issues have not arisen in my 83.
As to fuel lines circa exhaust. Oh, me. but, at speed, the air flow probably keeps the lines cool enough so as not to vapor lock.
Carl
Carl,
I wasn’t quite confused - it was the Dvorak keyboard I had in the back of my mind https://en.wikipedia.org/wiki/Dvorak_Simplified_Keyboard. And no, Germans type on QWERTZ keyboards as German language has hardly any "y"s, but plenty of “z”, especially in the “tz” combination. Still the same problem occurs here: standardisation sometimes leads to petrification of less than ideal solutions.
BTW, I haven’t heard of any safety related problems with the twin tank setup as used in series Jags. Stunt car drivers and banger racers loved them over decades, and most likely they wouldn’t have done so if they had been afraid that their cars would blow up any minute. My guess would rather be that the twin tank setup was abandoned in the XJ40, as this car was purposefully designed in a more conventional manner to cut production costs. When the four-spring inboard brakes IRS of our cars was replaced, Jaguar had a hard time to find a cheaper substitute with matching qualities. The hydraulic self-levelling suspension they came up with was pretty much of a failure - at the time it wasn’t mature yet, while today it has become business standard on premium cars. As regards tank setup, 5 series BMWs have used twin fuel tanks for the last 20 years at least (since the E39) with no negative effects I’m aware of.
In the 1960s electric fuel pumps were technologically advanced - my Spitfire still runs on a mechanical pump. The downside was reliability and dual pumps offered additional reliability. Maybe with the advent of FI and high pressure pumps this was considered less of an issue by Jaguar engineers. Maybe it also has to do with advertising speak - you don’t advertise you car with its properties in case of prior failure! Consumers want to be safe from failure in the first place.
Hopefully, you’ll get some better weather soon! We seem to be pretty much under way for spring. 70s have been forecast for next week.
Best wishes
Jochen
75 XJ6L 4.2 auto (UK spec)