Running on diesel – is it really all that efficient?

Petrol poised for a comeback as drivers question the cost savings of diesel cars

A driver fills his tank up with diesel. Diesel engines need to be driven at high migeage and not just on the school run, say experts. Photograph: Getty Images

A driver fills his tank up with diesel. Diesel engines need to be driven at high migeage and not just on the school run, say experts. Photograph: Getty Images


The price of some diesel cars will increase next year as a result of new emissions legislation being introduced, according to industry analysts. The EU 6 legislation is being brought in to reduce the levels of nitrogen oxide produced by diesel engines – seen by many as being even more harmful to health than CO2 emissions.

Peugeot Ireland expects an increase in prices because of the complexity of the work needed on diesel engines to reduce these emissions by more than half their current levels.

“There are a lot more issues with diesel engines in terms of reducing the levels than there are reducing emissions in petrol engines. There is a lot more work that has to be done,” says Peugeot’s sales manager, Colin Sheridan.

Other companies are not ruling out price increases because of the development of the new technology, but those with a bigger share of the market may be more likely to absorb any price increase in order to maintain their market share.

“I think the biggest problem here is for the smaller manufacturers that have not kept pace with the bigger ones, and they are struggling with the new technology,” said one analyst. “They will certainly be facing price increases. They have no choice but to comply and they don’t have the same capacity to absorb costs.”

Manufacturers and distributors also believe that as emissions drop further from next September, tax rates may well increase at the same time.

“As we go further down towards zero emissions, the tax rates may well follow,” says Sheridan.

There are no firm figures on the likely price rise, but most estimate it will be a few hundred euros. Any price increase – given the premium attached to diesel as distinct from petrol engines – will also add to the debate as to whether diesel is an economic alternative to petrol for many people. The improvements made to petrol engines recently have meant the gap has narrowed significantly.

Designed for high mileage
Many in the industry already concede that diesel cars simply don’t make sense for many drivers. Diesel engines are designed for high mileage but because of emissions-linked taxation they have become the preferred choice for the majority of Irish drivers.

Last year there were a higher percentage of diesel sales in Ireland than in France. One Ford executive has calculated that the minimum mileage for a diesel engine per annum is around 25,000 kms per annum – double the average mileage of many drivers. Diesel engines need prolonged heat to clear emissions efficiently, and the absence of higher-mileage driving is causing problems with diesel particulate filters (DPFs). The problem has become acute for many city drivers. Garages report that clogged DPFs are becoming increasingly common and are expensive to clear. In some cases they have to be replaced, costing several hundred euros.

“There are lots of people driving around thinking they are driving efficient cars, but diesel engines don’t even begin to clean emissions unless they are driven for longer periods,” said one Dublin mechanic. “Diesel cars on the school run are among the most polluting vehicles around. DPFs clogging are a major problem now and most people are very surprised to discover they have an expensive job on their hands. Not to mention the unexpected inconvenience.”

Some diesel engines burn harmful emissions at higher temperatures than others and this is adding to the problem. While some are capable of burning them at up to 1,000 degrees, others are not capable of burning them at more than 500 or 600 degrees. These engines are more susceptible to DPF clogging and damage.

Petrol popularity increasing
As petrol engines increase in both efficiency and performance, their popularity is increasing. Three years ago, for example, Peugeot 208 sales were almost 100 per cent diesel. Now the balance has shifted to 60/40 diesel to petrol. Skoda has also reported some shift towards petrol.

“I think we are definitely moving towards a more balanced market,” says Peugeot Ireland’s managing director, Des Cannon. Industry analysts point to engines like Ford’s 1.0-litre Ecoboost and Volkswagen’s TSi units as examples of how petrol technology has developed. BMW is also moving to smaller petrol engines and Opel will introduce a 1-litre turbo engine next year.

The motor industry has “brainwashed” customers into thinking of diesel as the only option since emissions- linked taxation was introduced, according to one observer. Given the fact that many diesel engines are being driven at urban speeds for limited journeys, the benefit of lower annual road tax can be outweighed very quickly because cruising speeds over longer distances are what deliver efficiency.

More and more buyers are now looking at the total cost of buying and owning a car now, says Colin Sheridan. “There is a huge focus on that now and people are realising that better small petrol engines are delivering power, economy and performance, and the tax differential has now narrowed significantly,” he says.