locking petrol cap causes non-start

Paulxmski · Post by **Paulxmski** » 02 Oct 2005, 06:56

Hi,
Thought it was a good idea to buy a locking petrol cap for my XMV6si.
First off noticed fuel guage needle reading high. Then later car wouldn't start. Removed locking cap put on old cap and it started first time. Didn't quite believe this was happening so tried again somewhile later, and again after a bit car would not start. I noticed that inside the non-locking camp there is a big O ring which is absent in the locking version which incidentally is not a piece of Cit kit. I think it maybe that the non-locking version creates pressure over the fuel by sealing the tank [?] Any ideas[?] [?] [:)]

citronut · Post by **citronut** » 02 Oct 2005, 13:52

usualy caps are vented,if it is ment to be and your new one is not it will cause a vaccum,i had this problem on my daughters 2CV,after we fitted an after market locking cap we purchased from GSF,suposed to be for the dersh,after it had been on for a while we started having running probs and fuel guage not working properly,then we noticed the tanke had sucked its self up in almost completly,and if you remove the filler cap there was a hiss of air inhaling,where the tank had gone up inside its self it had bent the sendor unit
regards malcolm

Mosser · Post by **Mosser** » 02 Oct 2005, 14:37

I would say it was more likely to be the little device that stops you overfilling your tank, there is a small button somewhere round the threads where your original fuel cap screws onto and presses the button in when you screw it on the last few threads, this releases some trapped air and i believe it also starts the fuel flow to the engine,
If your replacement locking petrol car doesnt have this deep flange around the threaded portion of the cap, then it wont press in the button, and the fuel flow is stopped and you wont get far
There is a litle trick you can do if you going to drive a long journey straight after filling up that allows you to fit in an extra 5-10 litres of fuel, all you do is to hold the little button in whilst your filling up and it releases the air before your tank if full and is replaced by fuel instead, expect a £100+ fillup bull with this method though !!