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The pros and cons of buying a diesel

Which should I buy – petrol or diesel?

Lots of car buyers struggle with this simple decision – which is best, petrol or diesel?

The truth is that there’s no one right answer. It depends on your priorities and the type of driving you do.

Con. Diesels cost more up front

It’s usually $2500-$5000 more for the diesel. The engine is more sophisticated, and needs to be more robust, and is produced in lower volumes – hence the additional up-front cost. But this is not all bad news because…

Pro. You get some of that additional cost back

When you sell the car, some of the premium you paid up front (new) is reflected in the value of the asset (used). In other words a used diesel Car A is worth more than a used petrol Car A … all other variables being equal.

Con. Diesel costs slightly more at the bowser

Different factors affect the price of diesel and the price of petrol at the pump. Diesel is more closely linked to the state of the world economy. (When things are booming, demand for diesel increases, and so does the price.) But because diesel engines drink 30 per cent less fuel than petrols, you’re not really comparing apples and apples.

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Pro. It’s more fuel efficient

Diesels deliver roughly 30 per cent better economy than equivalent petrol engines. They have more compression, so the expansion part of the cycle occurs over a greater range, delivering better economy.

Con. Diesels can need regular long trips

Diesels have particle filters in the exhaust to trap microscopic particles harmful to human health. Some highway running (say, every two weeks) is required for the filter to heat up sufficiently to burn off these injurious particles. (They call it ‘regeneration’.) If you don’t do that, the filter could clog and you’ll need a trip to the dealer to sort it out. So, if you do only short trips in the city, diesel might not be for you.

Pro. Diesel beats petrol at low revs

Diesels make three or four times the torque of a petrol engine at about 2000rpm. Because these are the revs you normally drive at, diesels feel unstoppable on hills, are ideal for towing and just generally pull without complaint. Petrols need to rev higher and even then usually can’t match the peak torque of the diesel.

Con. The diesel pump is less convenient

Diesel pumps out-number petrol pumps about eight to one – so, at an unfamiliar service station the diesel pump is always harder to find. It’s also dirtier, too, because diesel doesn’t evaporate like petrol does. You’ll smell like diesel after re-fuelling.

Pro. There are more available in 2016

The simple fact is that more vehicles today are offering diesel drivetrains. More choice means more sales.

2015 Volkswagen Jetta
2015 Volkswagen Jetta

Conclusion

If you intend to drive a lot of miles, it’s worth paying more upfront and going for a diesel. But if you don’t use your car that much, you’ll probably be better off paying a bit more for your fuel but much less for the car itself.