My current gas cap on the '59 Mark 1 doesn't make a tight fit and the rubber gasket under the cap is, shall we say, a little past it's prime.. It is a non-vented cap. The part number according to the parts catalogue is C 9024. I have found this part number at SNG Barrett; the picture of that cap clearly shows it is not vented. My research indicates that Jaguar went to a non-vented cap in about '62 on the Mark 2 as they devised a vented gas tank. I am assuming that my '59 Mark 1 did not have such a vented tank, thus I should use a vented cap. However, if the non-vented cap is the only one to be purchased nowadays, can I simply drill a small hole in the top of it and thus have a "vented" cap ? As always, thanks for your thoughts and assistance !
Schmitty

 

If the fuel tank has been replaced, not unlikely in 60+ years, it's likely that the tank is ventilated. The vent is a pinhole in the filler pipe. The pin hole breathes from a small tube, which, if it's still present, has some drain hose attached. I don't know if you can see the vent with the tank on the car (mine is dismantled).

​​​​If your tank isn't vented a small hole in the cap or a small groove cut in the sealing washer should be sufficient to allow air to flow in adequately. Of course, if you are not worried about originality, there may well be a variety of vented caps available. There's a lot be said for using one with a lock!

 

My information from bulletins shows that in July 1960 on Mk2, two changes were made to counter complaints about petrol smells in the car: A breather pipe was fitted to the filler neck, together with a non-vented filler cap. Mk1's never had this mod done. The Barratts site shows the Mk1 locking cap as vented. The stainless cap they show is claimed to be uprated. i.e. meant for use with a vented tank. The original Mk2 cap is clearly shown as vented.

The corollary of this is that non vented tanks had vented caps & that tanks with breathers had non-vented caps.

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if your current cap, "doesn't make a tight fit" then it's already vented. and unless you're filling it up to the tip-top it shouldn't present a problem. if it does, i think i would consider a new "groovy" cork gasket.

 

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Just make sure you know what tank is fitted to the car.
Basically, the MK1 and MK2 tanks are the same except for the venting.
Many years ago, I had a MK1 with a serious rust issue with holes on the top of the tank where mud and moisture can lurk between the tank and the boot floor.
I chased around for a replacement tank and finally ended up with a MK2 tank which I fitted to theMK1.
The only "hassle" is that the standard fuel gauge transmitter in a MK2 tank works on a different principle to the MK1 and consequently a MK1 transmitter must be used.