QuestionQUESTION: Hi Howard I have a 1980 series 3 Daimler sovereign 4.2 litre I have a problem with the fuel tanks right hand side is a new tank when I fill the tanks there is a strong petrol smell in the boot this smell goes away when both tanks are near empty. If I only fill one up I still get the smell. Also if the old tank is 3/4 full or more and it is a warm day if I am running of the new tank and park the old tank starts pouring petrol out of the filler cap. to me it seems that the new tank is filling up the old tank in you know what I mean. can you advise me
Les
ANSWER: Hi Les,
I don't know the Daimler but I am guessing it is about the same as a XJ-6 Jag which I do know.
The two tank system operates like this. A switching valve in the bottom of the trunk (boot) is selected for the right or left tank by a switch on the dash.
When the switching valve is powered when the right tank is selected and when the switch turns off the switching valve, the valve is spring loaded to select the left tank. Most of the fuel that is pumped forward is returned to the tank that is selected by use of return switching valves, one for each tank and they are located under a panel in each lower rear wheel well. The right switching valve is normally closed and only opens when current is applied to the fuel switching valve in the trunk. With current applied to both, the fuel is drawn from the right tank and returned to the right tank.
The left return valve is normally open and is only closed when current is applied, like when the right tank is selected.
When the left tank is selected, no current is applied to any valve, thus the right return valve is closed and the switching valve is in the left tank position and the left return valve is in it's open position. This was designed to be a fail-safe system so if you have any electrical failure, you can always operate on the left tank. (unless a valve sticks)
It is easy to test the "Return valve system" by starting the engine and just selecting the right tank and open both filler caps and with a flash light look into the filler necks and you should see fuel returning to the tank selected and not the other. Then switch tanks and look at both again and again you should see fuel returning to the tank selected and not the other. The trunk switching valve is more difficult to test. You can test the wire in the right position for power and see no power in the left position and put your hand on the valve while someone switches the valve back and forth to see if you can feel it "Click"
The smell of fuel may or may not be related to the switching system. I have over the years found several things that can cause that. One is the method they used to connect the filler neck and the tanks. It is a thin "O" ring and if the tank mounts are not adjusted correctly the neck is not sealed and each time you brake the fuel is forced up to the neck and fuel will run down the front of the tank and may even drip from the rear of each rear fender well.
Another problem is the vent system which runs plastic vent hoses forward all the way to just behind the right front head light bucket where there is a charcoal canister and a pressure valve that applies up to 3 PSI on the fuel tanks. This too can be easily tested by driving the car for a distance and then open the filler caps. This should cause a large rush of air from the tank when you open the cap. I believe that 3 PSI is too high and causes a lot of problems so on one car that was a constant problem I removed the spring from a 3 lb valve and adjusted the spring so it only had 1.5 PSI which solved that car.
Another problem is the routing of the vent hoses was inside the car under the parcel tray in the rear window then forward.
I don't know how much difference there is between our US version Jags and your Daimler but that is the best I can tell you.
Howard
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QUESTION: Thank you Howard for your advise I will take your advice on this weekend. For your information the Jaguar and Daimler are exactly the same car just different badges they come out of the same factory. I believe they where first called Daimlers and it has carried on as a sort of British snobbery I don't believe they are exported any longer. But what the hell I'm an Aussie and I just love driving them. I'll send you a photo for your web Site
AnswerI love them too even when I know most of their design flaws and short comings. I have two ser. III Jags that I drive. I have been asked why I have two and I have to tell them that when you own a series III Jag you need a back-up car for when it breaks. The trouble is that when your back-up car is also a series III you really need a third. ha!
It is good to hear that you have a Series III in Australia to keep the earth in balance. It would probably wobble if we were the only ones with them. ha! I just met a few Aussies at the Bonneville Salt Flats last month. A News crew, but I didn't get what station or city they were from and a couple of racers from Melbourne.
Send me that photo and I will put it on my site.
Howard
