Originally Posted by Lordofthewings
Valve cap - tiny component, big problem !

I had new tyres fitted a couple of weeks ago. After a few days, the rear offside tyre had gone completely flat. I had a chat to a couple of people independently and they suggested I examine the inside of the valve-cap.

When I bought the car it was fitted with four of the Morgan-logo ones, I found the original box and there was a spare one, which I fitted. Evidently it wasn't seating properly due to a flattened and crumbly tiny O-ring (much worse than the one shown front-right in the photo), which was depressing the centre of the valve, and resulting in a slowish and inaudible leak. Something I've never encountered before.

I swapped them around, and the same happened when I put it on the front. I have since tried three other types, and the problem has not recurred. So I have fitted new caps all round, and all the tyres are now holding 24psi. Can't say as I've ever looked inside a valve cap before, but in future I will !




If you tire is deflating this is caused by the the valve. You can change them separately, and it‘s worth to do this.
The valvecaps are only an extra safety. Sometimes you can get a set of o-rings at ALDI & Co, Halfords or Motorcycle shops.

Greets René

2018 plus4 (sports green)
with a homemade really shiny red tinted dash…