29. "Whooshing" Fuel Tanks in Series III XJ6 Jaguars

The Series III XJ6 Jaguar has a fuel vapor recovery system, which captures excess fuel vapors inside the charcoal canister located in the front right fender. Sometimes this system gets clogged or a pressure valve malfunctions, leading to a substantial vacuum in the fuel tank. The most noticeable symptom is a whooshing sound when you open the fuel tank filler caps. This whooshing sound is bad news. The vacuum builds up in the tank until the sides of the tank suck in a little. Then, when the filler caps are opened, the fuel tank expands back out. You can sometimes hear the tank popping back into shape. Do this a lot and the tank will crack from the flexing and start to leak. The usual suspect is a little valve right next to the charcoal canister, inline with a rubber hose leading to the canister. When that valve fails, the vacuum builds up. The only fix for this is to replace the valve. Fortunately, this "pressure valve", part number CAC3101 is pretty inexpensive at around $30. Ok, for a cheap little plastic part that's pretty darn expensive, but it's certainly cheaper than $470 for a new tank!

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