Diesels less reliable than petrols and pricier to fix, report claims

Diesels less reliable

As if diesel didn’t have enough on its plate, now experts are saying that cars powered by the fuel are less reliable than petrol motors. The majority of complaints around diesel have been down to its environmental credentials. However, a new report shows that diesel cars could be three times more likely to break down than their petrol equivalent and up to 20 per cent more expensive to fix.

How unreliable are diesel cars?

Car maintenance firm MotorEasy, which specialises in aftermarket warranties, studied 30,000 cars between the ages of three and eight years old. It found that diesel models were less reliable than petrol cars for seven out of 10 car makers (71 per cent).

Which diesel cars are worst?

According to MotorEasy, Alfa Romeo has the worst reputation for reliability with a failure rate of 47 per cent among its diesel models. That makes them four times more likely to fail than one of the Italian firm’s petrol cars. It’s followed by Land Rover on 41 per cent and Mitsubishi on 36 per cent. Saab and Mazda, both on 33 per cent, complete the bottom five. Kia and Mercedes are next with a 29 and 27 per cent failure rate. Vauxhall, MINI and Audi make up the remainder of the top 10, all on 26 per cent.

Diesels less reliable

Diesel Alfa Romeos such as the Giulietta are said to be 47 per cent more likely to break down than a petrol equivalent (Picture © Alfa Romeo)

Which diesel cars are the best?

Ironically Volkswagen, the brand that helped put diesel in the emissions spotlight, is one of the better manufacturers. And its Czech brand Skoda, which uses VW technology, was the best in the study. Just nine per cent of its diesel cars fail.

Why are they less reliable?

Petrol relies on spark plugs to cause the explosion in the cylinder that turns the cranks to eventually power the wheels. Diesel can’t do this because it is less flammable. As a result, diesel cars use what’s known as compression ignition. This prompts the explosion by putting the fuel under enormous pressure. It’s these high pressures throughout the engine that cause failures in components such as seals.

Why are diesel cars more expensive to fix?

The report says fixing a duff diesel could cost 20 per cent more than the equivalent repair to a petrol car. The average diesel car costs £517 to fix while for petrols the prices is £433. Diesels are more expensive because they operate under such high pressure. This requires fine tolerances and sturdier parts.

How to protect against a diesel failure?

The overarching advice to any car owner from Green Flag’s technical expert Nick Reid is to always stick to a car’s service schedule. This will ensure that many potential problems are nipped in the bud before they become catastrophically expensive. He said: “As an engine requires a lot of parts to move in perfect synchronicity, if you have a problem with one perhaps relatively cheap component, it can quickly escalate and become a very expensive failure.”

The advice from MotorEasy is to consider mileage if you’re looking at used diesels. Matthew Tumbridge, MotorEasy COO said: “To be clear: avoid diesel cars with over 100,000 miles on the clock. They will cost you money, time and hassle. Of course there are exceptions to every rule. But it isn’t worth taking a chance with these vehicles. If you must buy a high-mileage car, buy the petrol model with the largest engine.”

Drivers who cover low mileages around town should also avoid diesels as the Diesel Particulate Filter (DPF) is prone to clogging. Read more about this here.

2 comments on “Diesels less reliable than petrols and pricier to fix, report claims

  1. MATTHEW February 12, 2018 1:33 pm

    What a load of rubbish a 100,000 mile diesel engine is virtually just run in!

  2. terry harris February 16, 2018 9:45 pm

    a rubbish remark diesels are mote reliable, ive had them both, prefer diesel anytime,

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