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10 most expensive car repairs you didn’t see coming

Spanners for car repair

Which car repairs cost the most?

Car parts break and wear out – we all know that – but which fixes are the most expensive? We checked’s Car Repair Estimate Calculator to get repair costs for a regular petrol-powered VW Golf.

Costs for other makes and models will vary of course, but this gives a fair idea of routine mechanical failures that will leave the biggest dent in your wallet, and how much of the cost lies in the parts versus the labour – very useful information for cost-conscious home mechanics.

Catalytic converter cutaway

1 Catalytic converter

Total estimated cost: about £2200 (85% parts, 15% labour)

Catalytic converters are designed to give us a greener planet, but you’re going to turn pretty green yourself if you have to buy a new one. The good news is that they should last the life of the car; the bad news is a physical blow can damage the ‘cat’, as can an engine burning a lot of oil and the wrong kind of fuel additives.

You could save a little money by fitting the replacement part yourself, but most of the cost is in the part, which contains precious metals such as platinum, palladium and rhodium.

2 Clutch replacement

Estimated cost: about £1200 (53% parts, 47% labour)

Clutches wear out and you usually get a good deal of warning. There’s not much you can do to prevent it apart from maybe changing to a gentler driving style and not ‘riding’ the clutch.

There’s no real good news and bad news here – new clutch parts are pretty pricey, and while you can save money by doing the work yourself, the labour is a little under half the total cost.

3 A new ECU

Estimated cost: about £1200 (89% parts, 11% labour)

Another nasty surprise. Hands up everyone who thought the car’s ECU was a just little black box with a couple of transistors and a circuit board? In fact, a new ECU will cost as much as a specced-up laptop, and you’re not going to save a whole heap of cash by fitting it yourself.

This is a solid-state device with no moving parts to wear out and, in the ideal world, the ECU will last forever. The world, of course, is not ideal, so while your ECU shouldn’t fail, you shouldn’t rule it out.

Car alternator

4 Alternator replacement

Estimated cost: about £1140 (83% parts, 17% labour)

The alternator is one of those parts that you just take for granted, but they do wear out – and when the alternator dies, so does your car’s entire electrical system (albeit until you've fitted a new alternator).

Alternator lifespan estimates vary from 50,000 miles to 100,000 miles or more, but they don’t go on forever. They’re expensive little beasts, too, with not much to be saved by doing the fitting work yourself (unless you go for a cheaper used part).

More on how to test and replace an alternator here

5 Fuel injector replacement

Estimated cost: about £1060 (88% parts, 12% labour)

Fuel injectors are fantastic because they replaced carburettors, float bowls, needle valves and vacuum gauges. But fuel injectors stop being quite so fantastic if you have to pay for new ones.

What you might have hoped was nothing more than a glorified syringe turns out to be a little more complicated and a lot more expensive. They might last as long as the car. If not, they might last for as long as you own it. Let’s hope so.

Old head gasket

6 A new head gasket

Estimated cost: about £1030 (15% parts, 85% labour)

Head gaskets fit between the cylinder block and the head, and they keep the combustion chambers, oil and cooling systems separate – until they fail. That’s when you get oil in the cylinders, lots of blue smoke from the exhaust and a marked downturn in your popularity with the neighbours. It’s worse still if water gets into the cylinders because water doesn’t compress.

Annoyingly, the head gasket itself is pretty cheap, but the labour involved in getting the head off and skimming it (don’t skimp on the head skimming) is pretty huge. If you’re lucky, you may not get a head gasket failure for years, but it seems to happen most often with older, infrequently used cars.

7 Timing belt

Estimated cost: about £770 (52% parts, 48% labour)

This is an exceptionally tiresome and expensive bit of routine maintenance that you should never neglect. The timing belt (or chain) is what connects the crankshaft in the base of the engine with the camshaft in the top. If it fails or skips a couple of teeth on the cogs, the valves and the pistons may collide and wreck the engine.

So while it goes against the grain to replace a part that appears to be working perfectly, do it anyway. Your car’s manual or your local garage will tell you when, so make sure you listen.

More on how to check your timing belt here

Coolant leak car

8 Radiator replacement

Estimated cost: about £540 (40% parts, 60% labour)

Radiators can go on for years without problems, but yours can fail if your car gets a front-end knock or if you neglect to use a proper antifreeze mix when you fill it up – these have corrosion inhibitors and will also prevent frozen water expanding and damaging the radiator. 

If your car is losing coolant you shouldn’t immediately assume it’s the radiator, since there are lots of other hoses and couplings that can fail, too, and these are simpler, cheaper repairs. So make sure it’s definitely the radiator that’s faulty before you buy a new one.

More on finding the source of a coolant leak here

9 Starter motor replacement

Estimated cost: about £540 (76% parts, 24% labour)

There are few things worse than that horrible moment when you turn the ignition key and all you get is a feeble whirr, a couple of ticks or clonks from under the bonnet and an extended period of silence.

If you’re lucky, it’s just the battery, which is a relatively cheap and simple fix. If you’re not so lucky, it might be the starter motor. Often, these will go for years without problems, but sometimes they don’t.

10 Water pump replacement

Estimated cost: about £540 (40% parts, 60% labour)

The water pump is a small but vital part of your car’s cooling system that could last 50,000 miles, could last 100,000 and might never fail while you own the car. But if it does fail, the coolant no longer gets pumped through the radiator and around the engine, which quickly becomes rather hot and angry, as will you as you push your car to the nearest repair shop.

Water pump failures can happen on their own, but you can improve the odds by keeping your coolant system well maintained and topped up with proper antifreeze mix.