Diesel cars are more than three times as likely to break down as their petrol counterparts and are more expensive to fix when they do, according to data from car ownership and maintenance firm, MotorEasy.

Based on analysis of 30,000 faults on 3-8 year old cars across a 12-month period, MotorEasy found that the average engine repair bill for a diesel was £517, compared with £433 for a petrol model, a difference of 20%.

While the MotorEasy study looked only at used cars of three years old and above, with the majority likely to use older, Euro 5-compliant engines, it’s another blow for diesel vehicles; last November, the Government’s Budget announced that, from April, all new diesels will face higher taxation unless they adhere to a standard called Real Driving Emissions, Step 2 – a certification that will not exist until 2020.

With engine faults in particular being far more prevalent in diesels than petrol cars, the biggest repair cost found by MotorEasy amounted to an eye-watering £4,030.80.

Diesel cars are less reliable than petrol for more than seven in 10 manufacturers (71%), with Alfa Romeo oil-burners faring the worst against their petrol counterparts and experiencing a fault almost four times as often. The most reliable diesel cars are made by Skoda, with a failure rate of just 9%.

Diesel Unreliability 300x184 - Used Diesel vs Petrol, Motor Easy proves diesel three times more likely break down

Alfa Romeo, Land Rover, Kia and Mazda diesels have the highest average diesel engine repair cost versus petrol counterparts.

The higher rate of diesel engine failures is mostly down to the fact that diesel engines are under more pressure than petrol counterparts. Diesel units rely on self-compression, meaning that fuel is compressed to a much greater extent, putting more pressure on internal engine parts.

Only seven of 25 car makers analysed showed fewer breakdowns for diesel models – petrol-powered BMWs experienced faults 60% more often, while Audi, Skoda, MINI and Peugeot also bucked the trend.

Duncan McClure Fisher, founder of MotorEasy, said: “Diesels experience many more small problems than petrol cars. They are less reliable and, when a big item goes wrong, it costs a lot more to put right.

“If you’re still considering a used diesel car, our advice is to avoid high-mileage examples, particularly if you are only driving low mileage or doing city driving.”

For more information and top tips on buying used diesel cars, visit: https://www.motoreasy.com/Diesel-Car-Buying-Tips