Diesel vs petrol: What’s the difference?

There was a time when few car buyers considered diesel engines, simply because there weren’t many options. But they’re much more common on our roads today, with major brands introducing diesel options for some of their leading models. Head to Europe and you’ll see a significant uptake of diesel cars compared to back in Oz, but we’re a long way on from the days of diesel engines being solely the domain of 4WD enthusiasts.

Diesel engines have traditionally been seen as having three major advantages over petrol engines: 

• They have conventionally had greater range, resulting in more time between topups at the pump.
• They have traditionally boasted more fuel economy, making them cheaper to fill up in the long-run.
• They have always had the edge in terms of torque when compared with petrol engines. Great power from idle and ability to haul heavy loads with that torque positioned diesel engines as the perfect choice for utility vehicles, trucks and 4WDs. 

Things have shifted a little. The differences between diesel and petrol are less defined, as efficiencies across both fuel types have increased.

Which is cheaper to buy?

Diesel cars tend to be more expensive than petrol cars. However, with the integration of high-tech electronic injectors and common-rail systems into diesel engines – as well as the fuel efficiency advantage – a diesel engine may cost you less over the long-term. But costs can vary between individual models and drivers, so it’s hard to say which option is cheaper in the long-run, especially as car manufacturers continue to develop more efficient petrol and diesel engines at the same time.

To help you decide, look at the performance of the model you’re considering and then consider your own driving habits. For instance, if you’ll only drive the car to the shops a couple of times a week, you might choose a petrol engine, as many new diesel cars benefit from more regular driving so their self-cleaning systems can perform at their best. 

Diesel vs petrol performance

Diesel engines still boast that core difference of greater power in terms of torque. This means they’re still a favourite option for those vehicles that are hauling loads, such as utility trucks and 4WDs with caravans strapped to the back.

But beyond this important difference, petrol and diesel engines are becoming increasingly hard to separate in terms of their performance. New technologies, such as automated transmission improvements, self cleaning filters for diesel engines and improved fuel efficiency technologies have brought the diesel and petrol engines closer together. 

Which is cheaper to service?

Diesel engines require diesel-specific oils, filters and coolants, while many new diesels also have particulate filters that require you to drive the vehicle regularly so they can self-clean. This means it’s really important to stay on top of your maintenance for diesel engines. But on the other hand, the increased use of diesel across smaller car models means there’s more availability of parts and wider knowledge of how to service them.

If you’re looking to buy, you could consider ringing up a few mechanics and asking their thoughts on a particular model and asking them how much they tend to charge for regular services vs petrol engines. 

Which is better for the environment?

There is heated debate about the environmental credentials of diesel engines in comparison to petrol.

Diesel engines are often referred to as “lean-burn”. This means they use less fuel and more air to perform at the same level as a petrol engine, with overall CO₂ emissions of a diesel car being lower.

However, using that air means heating it in the engine, which produces toxic nitrogen oxides, nitrogen dioxide (NO₂), greenhouse gas nitrous oxide (N₂O) and nitric oxide (NO). Petrol cars use catalytic converters to clean this up, so they often emit less nitrogen dioxide.

Diesel engine makers today use ‘particulate filters’ to deal with this, which can clog up in urban environments, even if they automatically clean themselves. They often require you to drive for longer to work properly, which is why some new diesel models will have an alert to recommend driving longer to engage that self-cleaning system. 

How long does petrol last vs diesel? 

If stored well, petrol can last at least six months and even up to a year. Diesel has a similar shelf life, depending on storage conditions (such as temperature and humidity), but can cause damage if it begins to spoil and cause issues to your engine. You can purchase dedicated fuel storage cans, and make sure you keep them well away from any possible hazards, such as flames. 

If you head away, such as working overseas for half the year or more, and return to a car with petrol in it, there’s a chance it could be stale. Your car might struggle to start or stall when you accelerate. In this case, you’ll need to have it drained and replaced. 

Find coverage for your new car

Whether it’s petrol or diesel in your car, GIO provides a range of policies to match with your needs. Simply click below to explore the features of each policy and to get a free quote. 

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This advice has been prepared without taking into account your particular objectives, financial situations or needs, so you should consider whether it is appropriate for you before acting on it.