Why go for diesel cars

Is Forking Out The Extra For A Diesel Engine Always Worth It? James Stewart Finds Out

The Case Against:

Imagine you're in the market for a SUPERMINI car, something along the lines of a SEAT Ibiza, a Ford Fiesta or Renault's vogueish Modus. It's mainly going to be used for the school run and shopping, with the odd longer motorway jaunt. You sit down and estimate your annual mileage and it doesn't tot up to much more than 7,500 miles per year.

Now let's imagine you're going to own the vehicle for three years before you trade it in for something newer... We'll take the Modus as an example.

THE TECHNICAL BIT

Buy the £10,200 1.2-litre 16v Expression petrol model and over those three years you'll pour approximately £1,790 worth of unleaded fuel down it's neck. Opt for the similarly equipped £11,200 1.5dCi 80bhp Expression model and you'll pay £1,374 in fuel bills for the privilege of 22,500 miles of motoring. Therefore you have saved £416 on fuel bills, but in order to do so, you'll have forked out another £1,000 on your Modus.

The two per cent difference in residual values in favour of the diesel car shouldn't disguise the fact that it has depreciated by £5,751 over that period, whereas the petrol-engined model has had a mere £5,308 wiped off its value. Lower insurance quotes and servicing costs for the petrol car seal the deal. The sums don't work for diesel. Most buyers of superminis are better off opting for a petrol car.

The Case For:

Let's have some fun here. Taking the above figures and transposing them onto BMW's 330Ci Coupe Sport and its Coupe sibling, the diesel-engined 330Cd Sport, is highly illuminating:

THE TECHNICAL BIT

Given that these cars will cover higher mileages - say 12,000 miles per year at a conservative estimate - things are turned on their head. The £32,520 330Ci M Sport will drink £4,340 of petrol and depreciates by £13,860. The £32,950 330Cd, by comparison, consumes just £3,103 of diesel and sheds just £13,099 of its net worth. If you're a business user, the case is even more clear cut, with a 21 per cent tax liability for the 330Cd and a 29 per cent nobbling if you buy the 330i. The hefty 302lb/ft of torque from the diesel engine also puts the 221lb/ft figure the petrol engine generates firmly in the shade. Verdict

More often than not, the bigger the car you buy, the more favourable the diesel sums work out. The balance point seems to come in the family hatch sector where it usually comes down to personal choice. Many drivers now prefer the sinewy feel of a good turbo diesel engine over the more linear power delivery of a petrol powerplant. If you're looking for an executive car, an MPV or a 4x4, there's really no argument. It has to be diesel every time.

Published: February 2nd 2006