Choose between petrol or diesel power

08/09/10

Diesel cars? If you’re shopping for a car and have never driven a diesel before, it could be time for a rethink. Where they were once slow and noisy, the best modern ones are now as smooth and sweet-sounding as top-notch petrol motors. And they’re now even better than they were at delivering superior fuel economy and lower CO2 emissions.

As they’ve developed they’ve grown ever more popular with UK drivers. Now better than four of every 10 new cars is diesel powered even though they’re dearer than similar petrol-powered vehicles. Model for model, Volkswagen Golf-sized diesel cars cost typically £1000 more.

Even so, the fuel economy and taxation benefits are such that a growing number of companies are turning their car fleets over entirely to diesel.

Make no mistake, buyers’ preferences are swinging towards diesel and this is reflected in the high prices second-hand diesel models command compared to their petrol-fuelled cousins.

What you really need, though, is to work out which fuel type makes better sense. Here’s the motors.co.uk take on the issue:

Petrol
Cheaper: cars using this fuel type cost less; and you’ll save pennies at the pumps, too. Unleaded (at time of writing) costs 2.7 per litre less than diesel. At various times over the last two years petrol has cost the same as diesel and has also been as much as 13p per litre cheaper.
Choice. What’s more, there’s a bigger choice of petrol-powered cars, particularly if you’ll be buying second-hand, where two thirds of all the cars you’ll see take unleaded.
Petrol-engined cars can (usually) run further before needing an oil change and service.
You’re far less likely to put the wrong fuel in a petrol car. The nozzle of the diesel pump at your local filling station is wider than the one for unleaded and so shouldn’t fit the filler neck on your vehicle.
Fuel is cleaner and less smelly than diesel. Diesel fuel also becomes difficult to pump at winter temperatures because it thickens.
Cleaner at the exhaust. Diesels emit soot particles: petrols don’t.

Diesel
More economical: expect to travel 10 miles further per gallon than in a similar petrol-powered model.
Better for carbon dioxide emissions. Modern diesels typically have lower CO2 ratings. And most cars that benefit from CO2 ratings of 99k/km or less – low enough to qualify for free road tax – are diesel powered. That means you’ll pay less for road tax and, if your vehicle is company owned, it means you’ll pay less car benefit tax.
Great for towing. If you regularly need to pull a caravan or tow a trailer the strong low-revs urge of a diesel car is best suited to the job.
Longer lasting. Because of the higher pressures that diesel engines generate, they are built tougher. And they run at lower revs, too.
Simpler to service. Unlike petrol engines, diesels have no spark plugs to change.
More expensive to buy. New diesel cars typically cost more than their diesel counterparts. And newish second-hand diesel cars are often significantly dearer.

Which will be cheaper?
If you drive a lot of miles and expect to cover in excess of 20,000 miles a year, a diesel’s superior fuel economy should save you enough so that you’ll make back whatever extra you spent on the car quickly – say, within two years’ ownership. If most of your journeys are short and your annual mileage tots up to, say, 5000 or less, a petrol car will save you overall.

If you drive an average mileage of 10,000 miles annually, you’d need to own most diesels for as long as five years before you’d break even on costs. If you’re the sort that feels they must change up to another new car sooner than that, you’ll not recoup your cash.

So there’s no clear-cut answer. If you’re thinking of switching, work out the saving on your monthly car fuel bill that diesel will brings, add in a reduction in fuel tax (if any) and then calculate how many months it’ll be before you’ll claw back the extra a diesel’ll cost.

Of course, you might buy one just because you prefer how they drive... and, for us, there’s no better reason.