Hi guy's not had my xj for long, went to take the oil filler cap off but for the life of me couldn't work out how it releases. It just turned clicking ( what ever way it was turned ) like your petrol cap would once tightened.

 

Sometimes I have this problem when the engine is cold. Never when the engine is warmed up.

 

Lefty loosen.

If you ever get it off, replace it. Sounds like the plastic teeth inside are worn out.

You could try squirting some PB Blaster in the area where it rests against the valve cover. Let it work for a couple of minutes then try.

 

Had this happen to mine. It's worn out. Try applying some uneven lifting force to it as you turn it. Otherwise just pry it off. It comes out fairly easily.

 

Thanks people, had to prise it off, new on ordered.