With the huge fluctuations in fuel prices recently, one of the big questions, when buying a car, is whether to opt for petrol or diesel.
So which is best?
There’s no easy right or wrong answer. This decision can’t be based solely on which fuel is cheaper at the pump as there are many factors to consider:
- How many kilometres per year the vehicle will travel
- The size and type of vehicle
- The vehicle’s fuel economy
- Purchase price
- Depreciation
- Fuel price
- Road User Charge (RUC)
- Registration costs
- Service and maintenance costs
- Convenience
- Noise and performance
- Environmental impact
Size and type of vehicle
Large cars and 4WDs with high fuel consumption will benefit from being diesel powered. Smaller cars with petrol engines of around a 1.6 litre capacity will generally be very economical. However in general smaller cars will also travel shorter distances, therefore a number of qualifying factors come into play.
Fuel economy
During the AA Energywise rally 2008 we discovered diesel cars usually travel up to 30% further on one tank of fuel. However fuel economy should be considered in conjunction with other factors such as registration costs, Road User Charges (RUC), purchase price, servicing and depreciation.
Purchase price
Diesel cars used to be considerably more expensive than petrol. These days the price difference may not be as extreme, but it’s still worth checking.
Depreciation
Depreciation is a major factor when considering which fuel type to use. In particular, petrol models of large 4WD’s tend to depreciate more quickly than their diesel equivalents.
Fuel price
Although fuel prices fluctuate, diesel has remained cheaper at the pump. However, RUC and greater registration fees must be factored in to the overall running costs of diesel vehicles.
Road User Charge (RUC)
RUC costs apply to all vehicles over 3.5 tonnes and cars using fuel that isn’t taxed at source, such as diesel. For vehicles with a Mass Gross Weight of up to 2 tonnes, RUC costs $36.07 per 1000 km, so this needs to be considered as a direct additional cost of diesel.
Registration Costs
The annual registration fee is a cost that is fixed regardless of distance travelled. This is where higher mileage vehicles have an advantage over low mileage vehicles. The annual registration fee for a private car is currently $211.84 for petrol and $336.69 for diesel, a difference of $124.85.
Service and maintenance costs
Diesel vehicles have traditionally been more expensive to service. However, many modern diesels now have much longer service intervals – up to 40,000km or 2 years in some instances. Fuel filters are usually a recommended service item so this is a cost to be considered. However, service intervals depend on the manufacturer’s recommendation, so different makes and models will vary.
Convenience
Historically, diesel pumps were tucked away in the corner of the service station. This is usually no longer the case although may still be evident in remote areas. Ensuring the RUC is up to date is another potential inconvenience of operating a diesel vehicle. However, the biggest convenience of operating a diesel vehicle is it requires re-fuelling less often.
Noise and performance
Older diesel engines tend to be very noisy; however modern technology has greatly improved noise levels. Performance used to be poor for diesel vehicles, modern direct injection, turbo intercooled diesel engines means this is no longer an issue.
Environmental impact
Neither petrol nor diesel engines are good for the environment. However, minimising environmental damage should be of concern to all motorists.
- CO2 (Carbon dioxide) is one of the major greenhouse gases that has been linked to discussions on climate change. Generally, diesel engines emit a lower level of CO2 per kilometre travelled so could be considered better for the environment.
- CO (Carbon monoxide) is a lethal gas produced by petrol engines. While CO emissions have been combated with the use of catalytic convertors, they only work effectively once they have reached operating temperature, so CO is still a by-product of petrol engines during the warm-up phase.
- NOx (Nitrous Oxide) combines with low level ozone to form smog. While NOx can be higher in a new diesel than a new petrol engine, petrol engines produce more NOx over time.
- HC (Hydrocarbon) in fuels contains harmful chemicals including benzene. Benzene has been proved to be highly carcinogenic. HC emissions are much higher in petrol engines than diesel.
- SPM (Suspended Particulate Matter) refers to particles suspended in the air, such as soot, emitted from the exhaust of a diesel engine. While modern diesels are fitted with particulate filters, SPM emissions are still high in older diesel engines.
To summarise the environmental impact of petrol vs diesel engines: Diesel comes out on top with regards to CO2, CO and HC. Both are around the same when it comes to NOx and diesel is worse for SPM.
Generally speaking, a large 4WD vehicle doing high mileage would be better off diesel powered and a small hatchback, doing a low mileage may be better being petrol powered.
However, there are many factors to consider, and each factor needs to be considered in conjunction with the others. Ultimately, it comes down to the individual motorist’s decision as to which fuel best serves their purpose.
