Hi.

I was letting some air out of my tyres this morning and lost one of the valve stem dust caps.

I had no spare caps and was in a bit of a hurry, so I just drove off, thinking very little of it.

Myself and two friends went on a drive of about 65 miles, and we probably went up to around 60 mph.

When I got back from our trip I found the tyre which had no dust cap on the valve stem was completely flat. For all I know we could have been driving for most of our journey with a flat tyre, none of us noticed anything odd about the tyre during our trip.

 

Is it possible that because I was driving without the dust cap a lot of air leaked out of the tyre?

Edited 8 January, 20224 yr by 2006edr

Hi, more likely that the valve core didn't seat properly after letting some air out.

Surprised that you could not feel the flat tyre, possibly it didn't go flat until almost at end of trip. Are the tyres you have fitted run flats?

Some valve caps do have an O ring fitted and so can form a secondary seal - but their main purpose is to keep dirt out of the valve.

A good quick check for valve stem leakage is to wipe a film of spit over the top of the valve and watching it for a short time before replacing the cap - leakage is indicated if a film will not form.  

Hi.

I don't think the tyre that went flat is a run flat tyre, although I'm not 100% sure.

That's really good advice about testing the valve stem for a leak. I might try that. 

Thanks.

On 08/01/2022 at 22:34, Warrior193 said:

Hi, more likely that the valve core didn't seat properly after letting some air out.

Surprised that you could not feel the flat tyre, possibly it didn't go flat until almost at end of trip. Are the tyres you have fitted run flats?

Some valve caps do have an O ring fitted and so can form a secondary seal - but their main purpose is to keep dirt out of the valve.

A good quick check for valve stem leakage is to wipe a film of spit over the top of the valve and watching it for a short time before replacing the cap - leakage is indicated if a film will not form.  

vote +1

Pump the tyre up and see if air is leaking out of the valve. You can put a bit of soapy water on the end of the valve to check for air bubbles, if you can't hear or feel air coming out of the valve.

 

It's the valve core that is designed to stop the air leaking, not the valve cap. The valve cap's job is to stop dirt getting into the valve core, although the valve cap does provide a secondary seal.

 

Edited 10 January, 20224 yr by Carlston

Thanks for the replies.

I checked my suspect tyre again and the pressure had only dropped by maybe 2% overnight. (As compared with about 15% air loss the night before.)

I did the spit test today and film did form over the valve stem opening.

I'm taking the car to Halfords tomorrow for a free tyre safety test.

23 minutes ago, 2006edr said:

Thanks for the replies.

I checked my suspect tyre again and the pressure had only dropped by maybe 2% overnight. (As compared with about 15% air loss the night before.)

I did the spit test today and film did form over the valve stem opening.

I'm taking the car to Halfords tomorrow for a free tyre safety test.

 

If spit just formed a film, without an air bubble forming...then there's no air escaping...and therefore the valve is working.

 

If air is escaping, then you need to change the valve core.

 

This is the kind of tool that you need to change the valve core.

 

There's no need to overtighten the valve core, so don't use too much force.

 

 

https://www.ebay.co.uk/itm/184589472431?epid=1805249469&hash=item2afa63d2af:i:184589472431

 

10 valve cores (99p including postage)

https://www.ebay.co.uk/itm/160958141509?hash=item2579da5445:g:GRoAAMXQUY1Q~tNd

 

Edited 10 January, 20224 yr by Carlston

Eurocarparts are selling 4 valve cores for £1.09

https://www.eurocarparts.com/p/valve-cores-short-BAR321

 

Halfords are selling 4 valve cores for £5

https://www.halfords.com/tools/garage-equipment/breakdown-essentials/halfords-valve-cores-171862.html

 

A pack of 5 valve cores might be better, as some owners still have a spare wheel and might want to change all 5 valves cores on their car. However, I can't remember ever having to change one, although I always use valve caps (like you're suppose to) which keeps the dirt out of the valves.

 

Edited 10 January, 20224 yr by Carlston

On 08/01/2022 at 22:11, 2006edr said:

For all I know we could have been driving for most of our journey with a flat tyre, none of us noticed anything odd about the tyre during our trip.

If you've driven on a totally flat tyre then the internal structure will be damaged and potentially dangerous. Myself- I'd fit a new tyre (and valve!)

You may be right.

I'm taking it to Halfords today for a free tyre inspection.