Older diesel cars are three times more likely to breakdown than petrol models, a study shows.
And there is an extra blow for motorists as diesel cars can cost 20% more to fix when something goes wrong.
An analysis of 30,000 faults on cars three to eight years old found that the average engine repair bill for a diesel model is £517 compared with £433 for a petrol vehicle.
The study – over 12 months – by car maintenance firm Motoreasy also found that engine faults are far more prevalent in diesel than petrol models with the biggest repair bill amounting to an eye-watering £4,030.
The bad news comes as diesel drivers face a new blow with higher taxes for new models from April unless they meet stringent new emissions standards.
Diesel cars are less reliable than petrol for more than seven in 10 manufacturers (71%) with Alfa Romeo experiencing faults four times more than often than petrol models.
The most reliable diesel cars are made by Skoda with a failure rate of just 9%. The higher rate of diesel engine failures is mostly down to the fact that they 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.
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 alot 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.”
Meanwhile, new cars are safer than ever before with 1.8m now fitted with collision warning systems, according to the Society of Motor Manufacturers and Traders (SMMT).
New data shows that systems to lessen driver errors and prevent accidents are now available on almost seven in 10 cars on the market.
And the safety features have helped to reduce road accidents by 10% over the last five years.
The number of cars fitted with collision warning systems is up 20% on last year and drivers can pick from a raft of technologies available in car showrooms.
They include; utonomous emergency braking (AEB), parking assistance, adaptive cruise control and overtaking (or blind spot) sensors.
A system called 2 AEB, which automatically applies the brakes to avoid or reduce the effects of an impact, is available on more than half (53.1%) of new cars, with a quarter featuring the technology as standard.
Meanwhile, overtaking sensors are available to 42.1% of buyers and Adaptive Cruise Control, which allows the car to slow down and speed up automatically to keep safe pace with the vehicle in front, to 36.2%.
Mike Hawes, SMMT Chief Executive, said, “Safety is the number one priority for vehicle manufacturers and the pace of technological change is faster than ever before, with driver assistance technologies now available on the majority of vehicles cars.
“Fully autonomous cars may still be some way off but millions of consumers are already enjoying the benefits of new technology which can only help make our roads safer.”
“Thanks to these innovations and more, road accidents in the UK have fallen by nearly 10% over the past five years, and are set to fall further as manufacturers continually strive to develop ever more sophisticated technology to improve safety and the driver experience.”
Least reliable diesel cars