Petron

Try wearing rubber gloves, slightly damp

They seem to help by giving a better grip so your hand doesn't slip and you can put some muscle behind it

gbduo

I imagine it does tighten up from the differing co-efficient of expansion between the plastic and the aluminium rocker cover. Over time and heat, they will tighten. Its good really...

richmc

Wrap a cloth round it and use mole grips! thats what I do.

unclefester

When you put it back on - do make sure the rubber gasket is present - if it's not there, that may explain why the thing has cooked itself on

U9aXy6Dn

Mine gets fairly tight however i check the oil and undo the cap & then redo it at the same time.

Mole grips with a bit of rag over the jaws to protect the surface is how i'd do it if it got really tight.

Hedropsforglory

And the winner is...rag and molegrips.

Slightly disappointed as I was quite looking forward to the damp rubber gloves

Much appreciated all - back soon for the next thrilling installment of "bloke who hasn't maintained a car himself for 20 years trying to remember all he's forgot", no doubt!

richmc

And remember righty tighty, lefty loosey.

Bramblecat

Don't think this is specific to the original cap either. I have a Spoon aluminium cap and that has become 'locked on' on a couple of occassions. Have had to use hammer and wooden dowl to 'help' it off.