Do Valve Stem Dust Caps Prevent Large Amounts Of Air Escaping While Driving?

2006edr

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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 about 60 mph.

When we 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 the tyre for any reason during our trip.
Is it possible that because we were driving without the dust cap all of the air leaked out of the tyre through the valve stem just in the space of that trip?
 

MikeO

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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 about 60 mph.

When we 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 the tyre for any reason during our trip.
Is it possible that because we were driving without the dust cap all of the air leaked out of the tyre through the valve stem just in the space of that trip?

No - it's just coincidence. I've driven without a dust cap on a tyre for several hundred miles before getting around to replacing it.
Dust caps perform a function - they stop dirt and crap getting to the valve core. It seems you may have been unclucky and picked up a bit of grit or something that interfered with the valve core and let they air out.

Or - more likely - you have a puncture.

How on earth did you manage to drive on a flat and not notice?

If you've run on it flat, the tyre is toast, by the way - it will need to be replaced...
 

The Hood

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If you haven't got a puncture, you can buy replacement valve cores for a couple of pounds; it could be that yours is not sealing properly. They don't cost much and are easy to replace (you will need a removal tool). You can even get dust caps with a removal tool incorporated. A decent motor factor should stock them, or Halfrauds or Amazon. Just make sure you do it somewhere where you can blow the tyre up again from flat.
 

2006edr

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No - it's just coincidence. I've driven without a dust cap on a tyre for several hundred miles before getting around to replacing it.
Dust caps perform a function - they stop dirt and crap getting to the valve core. It seems you may have been unclucky and picked up a bit of grit or something that interfered with the valve core and let they air out.

Or - more likely - you have a puncture.

How on earth did you manage to drive on a flat and not notice?

If you've run on it flat, the tyre is toast, by the way - it will need to be replaced...
Thanks for the reply.
Neither myself or my friends noticed anything odd as we were driving - no strange noise coming from the tyre, no juddering. (It was a rear tyre.)
Someone mentioned it might only have gone flat at the end of our journey, which might go some way as to explain why none of us noticed anything while we were moving.
Checked suspect tyre this morning.
It's not a run flat and has lost about 15% of its air just sitting in the car park overnight.
 
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2006edr

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If you haven't got a puncture, you can buy replacement valve cores for a couple of pounds; it could be that yours is not sealing properly. They don't cost much and are easy to replace (you will need a removal tool). You can even get dust caps with a removal tool incorporated. A decent motor factor should stock them, or Halfrauds or Amazon. Just make sure you do it somewhere where you can blow the tyre up again from flat.
Thanks for replying.

I was thinking of spraying a bit of silicone into the valve stem in the hope it will lubricate the valve core and help it close and seal properly.
Whether this is a good idea I don't know.
 

MikeO

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Thanks for the reply.
Neither myself or my friends noticed anything odd as we were driving - no strange noise coming from the tyre, no juddering. (It was a rear tyre.)
Someone mentioned it might only have gone flat at the end of our journey, which might go some way as to explain why none of us noticed anything while we were moving.
Checked suspect tyre this morning.
It's not a run flat and has lost about 15% of its air just sitting in the car park overnight.
That's likely what has happened. If you take it to a tyre fitter, they'll be able to tell if the sidewall has been roached by being run on. The valve might be the culprit - they'll be able to fit a new one when they put the tyre back on...
 

The Hood

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If it is the valve leaking here are more spares than you will ever use in a lifetime for under a fiver from Amazon. Put some air in the tyre then some water in the top of the valve and watch for bubbles.

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2006edr

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I took my car to Halfords Autocentre today for a free tyre inspection.

Generally, quite a good service.

The technician told me there wasn't a lot wrong with the tyre, it was just more black than normal, I assume due to the rim pressing hard into the tyre for a while.

The report looked worse than his verbal assessment.

He also put on a new valve dust cap for free.

Thanks again for the advice.
 

The Hood

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It sounds like Halfrauds didn't check the valve for a leak. I would be inclined to put a drop of water in the valve and watch for bubbles the dust cap does not make an airtight seal the thread is only plastic. It would cost nothing to do just a minute of your time, running the tyre underinflated again could cause internal damage which would not be visible from the outside and ruin the tyre.
I certainly wouldn't spray silicone into the valve as the solvents and propellants could damage the sealing material.
 

2006edr

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It sounds like Halfrauds didn't check the valve for a leak. I would be inclined to put a drop of water in the valve and watch for bubbles the dust cap does not make an airtight seal the thread is only plastic. It would cost nothing to do just a minute of your time, running the tyre underinflated again could cause internal damage which would not be visible from the outside and ruin the tyre.
Hi.
I checked the tyre valve stem the other day for a leak using the 'spit test.'
It didn't have a leak, however just to be on the safe side I'll probably check it again.
 
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