Driver Knowledge Tests

Petrol vs diesel

If you are choosing a new car, should you go petrol or diesel? Diesel cars usually carry a price premium over petrol cars, but does the extra initial purchase price and servicing cost make it worthwhile?

Let’s assume you do enough kilometers to go through a tank of petrol each week – around 65 litres for most cars – and let’s assume the price of ULP is 120c and diesel is 140c, which is fairly indicative of recent prices.

Your petrol cost will be 65 litres x 52 weeks x 120c = $4056 (3380 litres)

Fuel economy

Diesel vehicles can be up to a third more fuel efficient than the equivalent model with a petrol engine, but the average is 20% according to a survey conducted by NRMA. However, diesel is more expensive than ULP – around 20c per litre. Based on our figures above you’ll use 2253 litres.

2704 * 140c = $3785

Difference in fuel cost: $271 per year.

Time savings plus less impulse purchases

Because you will fill up less at the service station you will save some time – the amount of time saved depending on how many times you need to fill up. If each fill takes you 10 minutes and you’d usually fill up every week, you will spend 520 minutes or 8h 40m per year. If you have to fill up one 20% less then you’ll save yourself 10 x 10m = just under 2 hours, which seems hardly worth it. However, if you tend to buy a $5 coffee every time you go, then the 10 times you’ll not have to go will save you $50. Again, not a great deal of savings.

Overall saving: $50 per year, plus a couple of hours of time.

Car costs

Diesel versions of a car can cost more than $2000 extra than the petrol version, but once they are 4 years old are only worth a couple of hundred dollars more.

If you spend $2000 more than you will have at least 7 years of fuel savings before you break even.

However, if you buy a car second hand then your fuel savings will pay for the difference in a year.

This doesn’t take into account servicing costs.


Older diesels usually require servicing more frequently than petrol cars. However, newer diesels often have similar service intervals and there’s not such a marked difference – perhaps only $50-100 per service.

Type of car

Diesel benefits larger vehicles like SUVs more than smaller vehicles. Generally, if the engine size is 1.6 litres or less, a twin charge (turbocharger + supercharger) can be almost as economical as an equivalent diesel.

Petrol models of large SUVs tend to depreciate faster than diesel models because those vehicles do use much more fuel and tend to be used for towing more.


Older diesel engines (and some cheaper new ones) can be much noisier than their petrol equivalents. Modern expensive diesels are exceptionally quiet, though.

Environmental impact

Diesels produce less carbon dioxide, carbon monoxide and hydrocarbons, but produce more diesel soot (suspended particulate matter).

Other ways to save money

You can save as much as 35% of your fuel bill by changing your driving habits. Check out this article for 10 tips to improve your fuel consumption. That will make up far more difference than getting stuck over whether to buy a petrol or diesel car.

In general, if you are buying a large SUV or you are travelling a lot, diesel will work out better. If you are driving a small car and not driving as far, petrol usually works out better.

Benefits of diesel

  • Better fuel economy
  • Less visits to the service station
  • Less opportunity for impulse purchases

Benefits of petrol

  • Cheaper purchase price on a similar car
  • Cheaper servicing costs
  • Less noisy

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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