Should I buy a diesel car?

Updated: 9 April 2024

Diesel cars have received some bad press in recent years and sales of new diesels have fallen dramatically. You may, therefore, be wondering whether you should buy a new or used diesel car.

For many people, diesel could still be a good option, but it pays to be aware of all the pros and cons before deciding. Here we explain everything you need to know.

The key benefit of diesel cars is that they generally use less fuel than petrol cars and some petrol-electric hybrids. That could save you money on fuel. Here’s some like-for-like examples, looking at official mpg figures: 

Ford Focus 1.0 EcoBoost 125PS – petrol – 55.54mpg

Ford Focus 1.5 EcoBlue 120PS – diesel – 67.3mpg

BMW 520i – petrol – 45.6mpg

BMW 520d – diesel – 58.9mpg

As you can see, the diesels give significantly better fuel economy than their petrol equivalents. And that’s true of every type of diesel car. Some, such as  the Peugeot 208, can give you more than 80mpg.

Better fuel economy means diesels can often go further between fill-ups than petrol cars, which could make them a great option for saving time and money if you do lots of long journeys. Some diesels, including certain models of Volkswagen Passat, can go more than 1,000 miles on a full tank.

Diesel cars generally have lower carbon dioxide (CO2) emissions than petrol cars. That can mean big savings on Vehicle Excise Duty (car tax), if your diesel car was sold new before April 2017. Cars sold before that date are taxed on a sliding scale, based on CO2 emissions, and large numbers of diesels are in the lowest brackets.

Those rules changed for cars sold new from April 2017, and most petrol and diesel models incur the same annual charge.

Diesel cars tend to be better for towing trailers and caravans because they have more torque – that’s the term used to describe an engine’s ‘pulling power’ rather than its outright power.

An engine with high torque is able to generate lots of force at low revs which is why vehicles such as lorries and tractors have engines built for maximum torque rather than maximum power.

Many older diesels emit more noxious pollutants – like nitrogen dioxide (NOx) and particulate matter – than petrol cars. These emissions reduce air quality and have been linked to serious respiratory problems, including asthma. However, the latest diesel cars have a range of features to reduce emissions, which means they are no more polluting than petrol cars.

Diesel models can cost more to buy than petrol cars, because the engines cost more to make. Diesel cars also have specific maintenance requirements. For example, many modern diesel cars use a fluid called AdBlue, which needs to be topped up regularly to keep the engine running properly.

Lots of diesel models also have a diesel particulate filter (DPF), which is part of the exhaust system and helps cleans up the gases expelled from the engine. Doing lots of short journeys can clog the filter to the point where it needs replacing, which can be costly. This means a diesel might not be the best option if you drive mostly in town. 

Diesel fuel also costs more at the pump than petrol, but if you drive long distances, the better mileage can cancel out the higher price.  

Petrol vs diesel cars: which should I buy?

What is AdBlue and does your diesel car need it?

What is a DPF?

Diesel engines often last longer than petrol engines. Like petrol engines, diesels generate power by burning a mixture of fuel and air. However, diesel fuel is less volatile than petrol and needs to be compressed for it to ignite and burn. That means diesel engines must be sturdier, which can help them last for many hundreds of thousands of miles, if properly maintained. 

Diesel sales have fallen dramatically in the UK over the past few years, from a high of 50% of total new car sales in 2010 to just 8% in 2023. Several factors explain the slump, including tax laws that favour low-emissions hybrid and electric cars, and the introduction of clean air zones that penalise cars with higher NOx and particulate emissions. 

More recently, a ban was announced on the sale of new petrol and diesel cars in the UK in 2035. 

There is, however, no suggestion that the sale of diesel fuel will end, so you should still be able to keep driving a diesel if you have one. However, prices for fossil fuels are very likely to increase over time.  

Many companies are developing non-oil-based, less-polluting alternatives to diesel that should be available in the next few years at similar, or even lower, prices. If you opt for a diesel car, you should be able to use it long after 2035.

Most diesel cars are likely to lose value over time but it’s very hard to accurately predict how much any car will depreciate and many used cars actually increased in value during 2021 and 2022.

Although diesel cars aren't as popular as they were it’s possible that prices will strengthen in the year or so before the ban on new ones takes effect in 2035. Why? Well, fewer diesels probably will be available on the used car market by then, so there could be less supply but more demand from buyers who either don’t want an electric car. 

You’ll find lots of used cars for sale at Cazoo, all available to buy through our trusted dealers.

Cazoo makes selling a car just as easy – just enter a few details for an instant online valuation. If you accept the offer our partners will get in touch to arrange payment and collection of your car at a time that suits you.