When should you change your cambelt?

A cambelt is the only part of your car that can destroy the engine without ever giving you a warning, a dashboard light or a bad MOT result. It sits behind a plastic cover where nobody looks, it does not wear out in a way you can see, and on most cars it will do its job perfectly right up until the morning it does not.

That is why the question is not does my cambelt look worn. It is how old is it, and how far has it gone. This guide sets out both numbers, why the second one catches out far more drivers than the first, and why neither the MOT nor your last service is evidence that the belt is fine.

When should you change your cambelt?

Most cars need a new cambelt somewhere between 40,000 and 100,000 miles, or every 4 to 10 years, whichever comes first. The RAC puts the range at every 50,000 to 100,000 miles or every 5 to 10 years. The AA quotes 40,000 to 100,000 miles or 4 or more years.

Those ranges are so wide that they are almost useless as a target, and that is the honest starting point. The only figure that means anything is the one printed for your exact engine in the handbook or the manufacturer service schedule. What the two sources agree on is the part most people get wrong: the interval is two limits, and you act on whichever one you reach first.

Two numbers, and the years one catches people out

Almost everybody thinks about a cambelt in miles. It is the number on the dashboard, it is the number in the advert when you buy the car, and it is the number a garage asks you for. The trouble is that the mileage limit is the one most drivers never get near.

A cambelt is rubber with fibre cords running through it. It hardens, loses its grip on the teeth and cracks with age whether the car is driven or not, and that ageing runs on the calendar, not the odometer. The RAC makes the point plainly: a belt that is ten years old with under 50,000 miles on it can be just as likely to fail as a belt that covered 100,000 miles in five years.

So the classic victim is not the high-mileage motorway car. It is the careful low-mileage one. A car first registered in 2017 doing 4,000 miles a year has covered around 36,000 miles by now, which sounds like nothing. On a 5 year or 6 year belt it is comfortably into its second interval and years overdue. The owner is thinking in miles and is nowhere near. The belt is thinking in years and is long past.

If you take one thing from this guide, take that. Check the date before you check the mileage.

Nobody is going to remind you

Two beliefs do more damage here than anything else: it passed its MOT so it must be fine, and the garage would have told me. Neither is true, and it is worth being precise about why.

The MOT does not check the cambelt at all. The DVSA MOT inspection manual for private passenger and light commercial vehicles is organised into eleven numbered sections, covering brakes, steering, visibility, lamps and electrical equipment, axles, wheels, tyres and suspension, body and structure, other equipment, nuisance, supplementary bus tests and seat belt installation. There is no section for the timing belt, because the MOT tests whether a car is roadworthy on the day, not the condition of parts sealed inside the engine. A car can pass its MOT without a single advisory the week before the belt lets go.

A service is better, but not by as much as people assume. On a lot of modern engines the belt sits behind a cover that is not removed during a routine service, so the garage is going on the age and mileage in front of them, exactly as you can. Where a belt is visible, a technician can spot cracking, fraying or a loose run, and that is worth having. What they cannot do is look at a healthy-looking belt and tell you it has another two years in it.

This is the difference between a cambelt and nearly everything else on the car. Brake pads get measured. Tyres get a tread depth. An MOT advisory gives you fair warning. The cambelt gets none of that, which is exactly why it is replaced to a schedule rather than on inspection.

Why the published intervals disagree so much

Put the well-known UK sources side by side and the spread is striking.

The ranges are wide because they are describing every engine sold in Britain at once. Manufacturers set the interval for a specific belt, in a specific engine, running at a specific temperature, and those decisions genuinely differ. Some engines are on 60,000 miles. Others go to 100,000 and more. Some are five years, some ten.

There is a second reason worth knowing. Manufacturers occasionally revise an interval downwards after a model is on the road, when real-world failures show the original figure was optimistic. If your car is older, the figure in a ten-year-old handbook may not be the figure the manufacturer would give you today, which is a good reason to ask a garage that works on your make rather than relying on the book alone.

What actually wears a cambelt out

Two cars on the same mileage can be in very different shape, because a few things age a belt faster than ordinary driving does.

• Heat. The belt runs in the hottest part of the engine bay. Repeated heat cycling is what hardens the rubber and eventually cracks it.
• Oil and coolant. A leak from a cam seal or the water pump soaks the belt and attacks the rubber. If you have a known oil leak near the front of the engine, treat the belt as a priority rather than a someday job.
• Standing still. A car laid up for months is not resting the belt. It is holding it bent around the same pulleys, which encourages flat spots and cracking.
• Short journeys. A lot of cold starts and short runs means more heat cycles for every mile covered.
• A failing tensioner or idler. These are replaced with the belt as a kit for a reason. A tired tensioner lets the belt slap and can throw a perfectly good belt off its teeth.

None of this changes the rule. It just means that if several of these apply to your car, the early end of the interval is the sensible end to work to.

Why a snapped cambelt is so expensive

Most modern engines are what mechanics call an interference design. The valves and the pistons pass through the same space at different moments, and the only thing keeping them apart is correct timing. Take the belt away and that timing disappears instantly while the engine is still turning at speed.

The AA describes the outcome directly: the engine could seize, causing the steering and brakes to fail, and the pistons can hit the valves and damage the engine. A non-interference or free-wheeling engine gets off far more lightly, because the pistons and valves never share the same space, but these are now the minority.

The repair is not one part. It is bent valves, often damaged guides and seats, sometimes pistons and the cylinder head itself, and all of it behind many hours of labour to strip and rebuild the top of the engine. On an older car the bill regularly exceeds what the car is worth, which is how a belt that was overdue turns into a write-off.

Set against that, the planned job is modest and predictable. This is the clearest example in car maintenance of a cheap job that exists solely to prevent an expensive one.

The warning signs, and why waiting for one is the wrong plan

The RAC does list symptoms that can point to a belt problem, and they are worth knowing:

• A ticking or slapping sound from the engine
• The engine stalling repeatedly
• The car refusing to start
• Shaking, bouncing or wobbling when idling
• Visible cracking or fraying, or a belt that is loose or out of line

Now the important caveat. Many belts give no warning whatsoever, and several of those symptoms mean the belt has already slipped a tooth, which is damage in progress rather than a heads-up. A new noise from the front of the engine is a reason to stop driving and book in, not a reason to finish the week. But an absence of noise is not evidence of anything at all.

That is the whole logic of an interval. You replace it before it can tell you anything, because by the time it can, you are usually paying for the engine as well. If a noise has appeared, read our guide on what an engine management light means too, since a slipped belt often sets a timing correlation fault.

Belt or chain: how to tell which you have

Before you budget for any of this, confirm your engine actually has a belt. Some use a timing chain instead, which runs in the engine oil and is generally designed to last the life of the engine rather than being replaced on a schedule.

A chain is not maintenance-free. Neglecting oil changes wears a chain early, and when a chain does need doing it is usually the bigger bill of the two. If it turns out you have one, what a timing chain replacement costs explains why those quotes vary so widely.

Doing the water pump at the same time

On many engines the water pump is driven by the cambelt and sits directly behind it. The AA notes that on some cars the timing belt has to come off to reach the water pump at all.

That matters because almost all of the cost here is labour to strip the front of the engine. With everything already apart, a new pump adds mostly parts. If the old pump fails a year later, you pay for that same strip-down twice, and a pump that seizes or leaks onto a new belt can take the belt with it. Fitting both together is the default recommendation for good reason, and the tensioner and idlers normally come in the same kit.

Buying a used car with no cambelt history

This is where real money gets lost. A seller saying the belt was probably done, or that the car is too low mileage to need it, is not history. Only a receipt or a stamped record naming the job is.

Assume the worst and price it in. A belt and pump on an unknown car is a few hundred pounds. Guessing wrong costs you an engine. When you view the car, ask for the invoice, check it names the belt and ideally the water pump, and check the date as well as the mileage on it. Our guide to what a full service history should contain covers what good paperwork looks like.

If there is no proof, budget to have it done straight away. It is far cheaper to fit a belt that had a year left than to gamble on one that was already three years over.

What a cambelt change costs

The RAC puts the average cambelt replacement at around £430 including parts and labour, with manufacturer averages running from about £409 on a Fiat to £783 on a MINI. The AA quotes a broader £250 to over £500, rising past £1,000 on some luxury cars. Adding the water pump typically lifts the total by a modest amount rather than doubling it, because the labour is shared.

For the full breakdown, including what a fair quote should itemise and how to compare garages properly on this job, see how much a cambelt replacement costs. It also helps to see the figure next to ordinary car servicing costs, since a cambelt is an occasional big-ticket job rather than a yearly one.

What to do this week

Three steps, and the first two are free.

1. Find out whether you have a belt or a chain. The handbook will say, or any garage can tell you from your registration.
2. If it is a belt, write down both limits, the years and the miles, and the date and mileage of the last change. No record means treat it as due.
3. Book it if either limit has passed, or is close. Ask for the belt, tensioner, idlers and water pump as a kit, and keep the invoice with the service history.

If you need someone to do it, you can compare local garages on YourCarGarage and book with an independent near you. Many will quote for a belt and water pump kit over the phone if you give them the registration, and it is well worth getting two or three quotes on a job of this size. Keeping to your wider service schedule makes the belt far easier to keep track of.