Squirting WD40 on expansion bottle lid?!

[northernchappy]

a mechanic, said the lid on my fiesta zetec was tight, he took it off and squirted lots of WD40 on the inside of the lid, before screwing it back on. I drove it 3 miles home, then rubbed it all off. I looked into the coolant fluid but couldn't tell if any dripped into the coolant. The wd40 left a white thickish deposit on the inside of the lid

Will the coolant be ok? Was it ok to do what he did?

 

[Burnerman]

Nothing to worry about there, any coolant contamination would be minimal and can be ignored.
Sometimes these caps are ridiculously tight to remove and I've known two that broke up on removal so I guess he was just trying to prevent this.
More frequent removal helps but years can go by without the need to remove them!
John

 

[northernchappy]

Thanks, im a auspicious bugger lol

Much appreciated

 

[Vicario]

I broke the cap (Chevvy Aveo). I got a new one and the bloke in the spares department advised me to smear the thread with a bit of vaseline every year or two.

 

[Gasguru]

A bit of silicon grease should do the job...get the same issues on all the plastic heating filters.