The tin of liquid and the little electric pump that many new cars carry instead of a spare can feel mysterious until they are needed. In fact a sealant kit is simple, and so are its limits, which are the most important thing to understand before relying on one.
How it works
A repair kit is a bottle of sealant and a small compressor that runs off the car's 12-volt socket. The usual process is:
- Connect the kit and inject the sealant through the tyre valve
- Inflate the tyre with the compressor to the recommended pressure
- Drive a short distance so the sealant spreads around inside and plugs the hole
- Recheck the pressure and top up if needed
The sealant coats the inside of the tyre and seals a small puncture from within, getting the car moving again without a wheel change.
What it can and cannot fix
This is the part that matters most. A sealant kit handles:
- Small punctures in the tread: a nail or screw hole up to a few millimetres
It cannot deal with:
- Sidewall damage of any kind, as covered in the sidewall damage guide
- Large holes, cuts or splits
- A blowout or a tyre that has come off the rim
In other words, it fixes the same small tread punctures that could be properly repaired anyway, and nothing outside that.
A temporary measure
Sealant is a get-to-a-garage fix, not a permanent one. After using it:
- Keep to the kit's speed limit, usually around 50 mph
- Drive only as far as needed to reach help
- Have the tyre inspected and properly repaired or replaced soon after
Tell the fitter
One practical point: always tell the fitter that sealant has been used. It coats the inside of the tyre and can make a proper repair messier, and some types complicate it. A fitter who knows can clean it out and assess the tyre properly. It is also worth knowing that sealant bottles have an expiry date, the chemicals degrade, so the kit is worth checking occasionally so it actually works when the day comes.
From the workshop: the goo gets a bad name, but for a nail in the tread on a dark wet night, it's brilliant, beats kneeling in a puddle with a jack. Just remember it's temporary, keep it slow, and warn whoever fixes the tyre that you've used it. They'll thank you for the heads-up.
Sources and accuracy. The description and limits here reflect common manufacturer practice at the time of writing and vary by kit; the instructions with the car are definitive. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
How does tyre sealant work?+
The kit injects liquid sealant through the tyre valve and then inflates the tyre with a small compressor. Driving a short distance spreads the sealant inside, where it plugs a small puncture from within. It is a temporary get-you-going fix, not a permanent repair.
What punctures can a sealant kit fix?+
Only small punctures in the tread, a nail or screw hole up to a few millimetres. It cannot fix sidewall damage, large holes, cuts, or a tyre that has come off the rim or blown out. For those, the tyre needs replacing.
How far can you drive after using tyre sealant?+
Only far enough to reach a garage, and at reduced speed, typically around 50 mph. The sealant is a temporary measure, so the tyre should be inspected and properly repaired or replaced as soon as possible afterwards.
Does tyre sealant ruin the tyre?+
Not necessarily, but it can make a later proper repair messier, and some types complicate it. Always tell the fitter that sealant has been used so they can clean it out and assess the tyre properly rather than being caught out by it.