Jaguar XJ-S Coupe
Fuel Tank Leaks due to Steenkin' Rivet
Fuel tank leaks are, in turn, sometimes caused by stress cracks or separated joints due to excessive pressures and vacuums being applied by a defective vent system. Sometimes they are caused by the bottom of the tank rusting from the outside, often because the rear windshield seal is leaking and allowing water to soak into the foam the tank sits on. And sometimes the tank leaks are caused by a steenkin' rivet that someone at Jaguar thought would be a good idea to install in the bodywork underneath the tank.
There is a tube that goes along the bottom of the car and over the IRS. This tube is held in place by little plastic clips that are pop-riveted to the car. One of these pop rivets comes through the panel the fuel tank sits on. The panel has a 1/4" layer of foam on top, and the tank sits on that; the popped side of that pop rivet is a little shorter than the foam is thick, so it doesn't touch the bottom surface of the tank. The foam, however, compresses with age and the weight of a full fuel tank sitting on it, so eventually the tank is hard against the tip of the pop rivet. Then, after some more miles and more vibration, the rivet wears a little hole in the tank. The tank then leaks and fills the surrounding foam with fuel.
There is no way to either prevent or fix this problem without removing the tank. When the tank is out, prevention is easy: grind the end of that rivet off so it cannot possibly touch the tank. You can easily leave enough of the rivet in place so that it still holds the clip and the tube underneath. You can also opt to add more foam or replace the OEM foam with something thicker, lifting the tank a little higher above the rivet.
To help owners find the rivet, here's a pic:
This is Kirby Palm's '83; that is apparently a very clean car, no rust to speak of and no visible signs of ever having had a rear windshield seal leak.
Of course, you can't actually see the 1/8" rivet in the pic. The grey spot in the location indicated is actually where Palm cut a 1" circle out of the foam pad, after which he ground the rivet down where it couldn't possibly cause any trouble.
If the rivet has already made a hole in the tank, this is an easy leak to fix. Auto parts stores sell a two-part epoxy especially designed for sealing fuel tanks. If they don't have it, just get some J B Weld; it'll work too. Or, braze the hole shut.
While the tank is out, there are several other things that definitely
should be done. Top priority is to clean the outside bottom of the
tank and apply rustproofing. Other good ideas include replacing all
of the hoses if they're more than ten years old or so, upgrading
the fuel filler, and coating the inside of the fuel tank, surge tank,
and vapor separator with Bill
Hirsch Fuel Tank Sealer.
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