Over the past few years, diesel’s reputation has been torn to shreds, resulting in a big drop in the sales of new diesel-engined cars. Some of this drop is because of the headlines and much of it is because of uncertainty about what will happen in the near future. So should you buy a new diesel-engined car? Predictably, there are lots of things to take into account.

The UK government introduced higher first-year tax rates for diesels registered after 1 April 2018, there have been scare stories of used values collapsing and you don’t have to look far to see headlines of 40,000 people dying prematurely because of diesel-powered vehicles. Get taken in by the hype and you’d never consider buying a new diesel, but the truth doesn’t match up to the headlines.

For most people there are three key reasons to buy diesel: lower running costs, a better environment (really??) and because of the driving experience. (taxation is one – is that included in running costs?) Some of these things are starting to become reasons to avoid diesel (or so the headlines would have you believe), and in this regard another factor is likely to come into play: restrictions on diesel car use. Here’s the reality.

Running costs

The thing with running costs is that they go far beyond just the cost of the fuel, which is all that many buyers consider. But you must also take into account the higher initial purchase cost of the vehicle (compared with petrol), the slightly higher price of the fuel, the servicing costs (which may or may not be higher than a petrol-powered equivalent) and the cost of any repairs, because diesel engines are generally more complicated than petrol units, so potentially less reliable and therefore can be more expensive to maintain.

There’s also road tax to consider, although most people pay a flat rate of £140 per year; cars priced over £40,000 attract a £320 extra charge whether they have a petrol engine or a diesel. There’s also the first year ‘showroom tax’ to pay, with diesels paying a penalty by moving up one road tax band. This can be as little as £15 per year or as much as £520, but for most cars that first year penalty is just £20-£40. It’s all spelled out at https://www.gov.uk/vehicle-tax-rate-tables.

To put things into context, a 148bhp Ford Focus 2.0-litre diesel is rated at 114g/km, which means a first-year charge of £210. But a Focus with the 148bhp 1.5-litre petrol engine is rated at 133g/km, which means it also is subject to a first-year charge of £210. Meanwhile, a 194bhp Mercedes E220d estate comes with a 2.0-litre diesel engine and is rated at 129g/km of CO2, which means a first-year rate of £210. The alternative petrol model is the 184bhp E200d estate (which also has a 2.0-litre engine); with CO2 emissions of 161g/km it attracts a first-year charge of £530. So even with diesels paying a penalty, the cost is usually no higher than for an equivalent petrol-engined model.

For many, better fuel economy is the key reason for buying diesel, and is it any wonder when a 3.0-litre diesel engine will offer as much muscle as a 5.0-litre petrol, but in an SUV the former will typically deliver 30-35mpg compared with the typically 20mpg of the latter? As petrol-electric hybrid cars become increasingly mainstream, the on-paper fuel economy might seem enticing and the first-year road tax will probably be lower because of the lower CO2 rating. But the real-world fuel costs are still likely to be higher than for an equivalent diesel, unless you do a lot of stop-start driving.

Air quality

We were encouraged to go diesel because of the lower CO2 emissions, but there’s far more to an engine’s emissions than merely carbon dioxide. A cocktail of poisonous chemicals including nitrogen oxides and particulates also spew out of a car’s exhaust, and it’s these that have given the diesel engine such a terrible reputation.

Every few years the limits for exhaust emissions are tightened up. The current set is known as Euro 6, and all cars sold since September 2015 have had to comply. While older diesels were pretty dirty, the latest models have to be just about as clean as their petrol counterparts.

And that figure of 40,000 premature deaths because of poor air quality? Firstly, that’s for air quality as a whole, and the blame for that can’t be entirely aimed at diesel-engined cars. Most importantly though, it’s a worst-case scenario estimate of the number of already ill people whose deaths may or may not have been brought forward by an unknown amount. There’s a more complete explanation here, but the bottom line is that the figure needs to be taken with a large pinch of salt.

The driving experience

Petrol engines don’t have as much torque, or pulling power, as diesels. As a result you have to rev a petrol engine more, and if you drive a large vehicle such as an SUV you’ll find this takes its toll on fuel economy, especially if you tow a caravan. This is why buses and lorries don’t have petrol engines; they need the muscle of a diesel because they’re so big and heavy.

Also, because diesel engines have more muscle the gearing can be raised, which means that on a motorway journey the engine is turning more slowly so it’s using less fuel and the cruising is more relaxed. Diesel engines don’t rev as high as petrol units and they don’t sound as nice (not sure that is still the case – diesel engines as quiet as petrol now), but for anybody whose car is merely transport (and that’s most of us), a diesel will fit the bill quite nicely.

Restrictions

This is why many people are shying away from diesel; they don’t know what restrictions might be imposed on them in the future. As local authorities queue up to charge car owners more to park or to enter cities, the fear is that by opting for a diesel car the costs might spiral. However, the focus of these restrictions so far seems to be pre-Euro 4 petrol cars and pre-Euro 6 diesels, so any new car should remain unaffected by restrictions. But there are no guarantees…

Verdict

So – should you buy a new diesel car? From a running costs point of view you should still be quids in and from an environmental point of view it’s the same. The unknown is the restrictions that might be brought in. However, pre-Euro 6 cars are the ones most likely to be targeted, so when it comes to buying a new car, in many cases opting for diesel can still make a lot of sense.

Richard Dredge

July 2019