/ Motoring

Would you still buy a diesel?

Amid headlines of manufacturers cheating emission tests and the harmful effects of NOx on our health, is there any room left for a defence of diesel?

Diesels are distinctly out of fashion. With consumer confidence in them shot after various emissions scandals, higher UK road taxes, new MOT rules and some cities around the world banning them outright, driving a diesel seems to be becoming taboo.

Add to this growing public awareness of the effects of NOx emissions and the subsequent plummeting sales, and it seems it may be curtains for diesels.

Decline and fall

Since VW’s ‘Dieselgate’ rocked the world in 2015, sales of diesel cars have plummeted in the UK, falling from 50.1% of overall new car sales in 2014 to just 31.9% as of July, according to data published by the SMMT (Society of Motoring Manufacturers and Traders).

And it’s not without reason. Public awareness about NOx (oxides of nitrogen) emissions from diesels – linked to tens of thousands of premature deaths around the world – has grown massively.

Air pollution from vehicle emissions is a very real problem. In 2017, for example, it took just five days for Brixton Road in London to break its NO2 (nitrogen dioxide) limit for the entire year.

And the results from our new research paints a fairly dirty picture for diesel: on average, the 61 diesel cars we tested produced 0.27g/km of NOx – nearly three and a half times the official Euro 6 limit (0.08g/km).

Diesel defence

But does it have to be this way? Diesels generally produce less carbon dioxide (CO2) and carbon monoxide (CO) than equivalent petrol cars.

And they don’t inherently have to be NOx-spewing monsters. Some manufacturers are starting to produce some squeaky clean diesel cars.

Currently they are the exception rather than the rule, but we’ve found two Mercedes and one BMW diesel car that produce less or the same NOx emissions as your average petrol.

AdBlue & SCR make a difference

More and more diesel cars are using Selective Catalytic Reduction (SCR). It’s an active emissions system that injects urea, most commonly AdBlue, into the exhaust system to cancel out harmful emissions.

And it makes difference. We found that diesel cars with an SCR system, on average, produced about a third of the NOx than cars without one.

So fitting these systems on all diesels could make a huge difference to NOx emissions.

But it’s really a question of whether manufacturers think it’s worth the cost to add these sophisticated systems to their entire range of diesel cars – something that will no doubt be influenced by the tough new on-road emission tests that will be in force for all new cars by September 2019, known as RDE step 1, and will require better real-life emission control than before.

Room for reform?

Some manufacturers clearly do think there’s public appetite for cleaner diesels, a Mercedes spokesperson telling us previously:

‘Our new engines are both highly efficient and produce low levels of NOx. It’s a fact that it’s worth improving the modern diesel instead of banning it.’

That’s one opinion, but it is true that relatively ‘clean’ diesel cars are possible – and available, if you’re willing to pay for them.

The problem is these ‘clean’ examples really are the exception and, it seems, time may already have been called on diesel generally.

But what do you think? Do you agree that diesel has a future if it can be improved? Is the public snubbing of diesel going too far?

What about if someone presented you with a clean diesel car – it produces less NOx, CO2 and CO, and costs the same as an equivalent petrol car – would you buy it or not?

Robert Tomlinson says:
6 September 2018

Transport for London says, in connection with the proposed ULEZs, that retro fitting emissions reduction technology is unlikely to become available for cars and small vans, because it would too expensive to develop. Is this pessimistic view generally accepted? Will Which be monitoring how the situation might evolve?
Robert T


They have a site about filters, but this seems only to include commercial vehicles:
Petrol cars since 2005 are OK, but diesels sold before Sept 2015 may not be Euro 6. I guess converting them will be uneconomic so best to sell before the rush and buy a compliant car. however, seems to be some moves in Germany to reduce NOx emiisions in older cars http://europe.autonews.com/article/20170802/ANE/170809901/automakers-offer-to-upgrade-5-million-diesel-cars-in-germany
This site shows a retrofit filter designed for bigger vehicles http://www.wandhgroup.co.uk/index.php/ulez


From what I have read, there simply is not room for these modifications in most modern cars, where the engine is crammed into such a small space that even a routine maintenance job such as changing the timing belt is a difficult and expensive job. On commercial vehicles, more space is available to fit diesel particulate filters and reservoirs for urea solution, both of which are bulky.

mark hancock says:
8 September 2018

Air Quality is the biggest health emergency bar none (wars, obesity) worldwide and where I live in Southampton. I cannot see any discussion on particulates which are known to be hazardous, especially the very fine PM2.5’s, known to cross membranes even into the brain and affect babies in the womb. Bad, we just don’t know how bad. Diesels I believe produce very much more particulate as well in general as NOx than Petrol. Electric cars produce the same tyre but less brake dust (due to regenerative braking) but the health cost are very much less at only £13 a year. Averages for diesel cars is £258 per year, petrot £37 a year. We love our electric car (a Nissan Leaf) which we bought second hand (for £8000) and does nearly everything we need – but for that which it, train, e-bicycle or bicycle do not, we very occasionally hire a car for short periods. It works out so much cheaper. Hybrids are an unsatisfactory halfway house for us – more complex and expensive, and all that polluting fossil fuel gubbins has be dragged around with you all the time. The main hurdle is whether you can charge (cheaply) at home. Houses without their own parking place and flats need investment & regulation from Government via councils.

Roger Scammell says:
2 October 2018

Those health costs look impressive, but where do they come from and what else should be in the equation? Until the government can sort out a transport policy that makes the train a more viable option, then electric cars only work for very short journeys and commutes, so car hire remains the alternative. It is still much less convenient to collect a car from some place miles away than to walk to one outside your house. At present convenience wins over the cost argument!

Nigel Reese says:
1 January 2019

Modern diesels are hard to beat, the hysteria whipped up around the VAG cheating software and the obvious problems with old diesels has skewed the debate. The high levels of NOX exist as a by product of highly efficient high temperature combustion, they occur in less efficient lean burn petrol engine emissions too. We are in danger of throwing out the baby with the bath water. Battery power will have significant impact on our environment, not least our ability to supply the power to recharge them:10,000 miles driven is approx equivalent to the total power used in a 4 bed house per year. We need to invest in a variety of solutions, and efficient clean diesels are part of the solution.