Petrol or diesel, it's a personal matter: Car Choices Part 3
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The car buying process is littered with choices that aren’t always obvious. As we walk through the steps of choosing, buying and owning a car we looked at new, used or ‘nused’ in Car Choices Part 1, how to finance it in Car Choices Part 2, and now with those aspects covered off, we can deal one of the final questions before making a decision, and one which has evolved over the years: which fuel, petrol, diesel or hybrid?
It’s fair to say that diesel has fallen out of favour for passenger cars over recent years, partly thanks to negative publicity surrounding the “dieselgate” emissions scandal and partly thanks to huge progress made in the performance characteristics and fuel efficiency of petrol powerplants.
But diesel is still very much out there and a viable option, especially for larger vehicles and/or those covering greater-than-average annual mileage. So what should you consider when making a powertrain choice?
Diesel fuel contains more energy than petrol and so it burns more efficiently – you will generally go further (often much further) on a litre of diesel than you will on a litre of petrol.
Turbo diesel engines also generally produce more torque than equivalent petrol powerplants, so they can feel more relaxed to drive: lots of pulling power very low down in the rev range.
If you do a lot of open-road driving and/or cover long distances, and regularly tow heavy loads, diesel power is ideal.
Diesel is also significantly cheaper at the pump, so with the added range, there’s also the psychological perception of cheaper fills each week.
Petrol is still the default choice for passenger vehicles, so there’s much more model choice out there. Unless you’re buying a ute, which are mostly diesel.
If buying a new or near-new car or SUV, many modern turbo-petrol engines have really narrowed the gap to diesel in terms of torque and fuel economy.
Petrol engines also have a much greater rev range than diesels and produce peak power at higher speed, so they’re arguably more intuitive/rewarding to drive: with a petrol you simply rev it more to go faster which makes sense to most people, whereas with a diesel you might have to think more about using the mid-range of the engine to get the best out of it.
All Government taxes are also paid at the pump when you fill up with petrol, which is nice and simple. With diesel, you have to pay the Road User Charge (RUC) separately, which is an extra admin and cost hassle.
Petrol cars are cheaper than diesel to purchase, but they also burn more fuel per kilometre. Diesel fuel is cheaper at the pump, but then you have the extra cost of RUC. Comparing like-for-like is a bit of a head-scratcher, but NZ Transport has an online petrol vs diesel calculator to work out which is best for each specific case based on yearly km, fuel economy and fuel price.
But let’s do it by lining up the Hyundai Tucson Series II 1.6T Limited petrol with its diesel equivalent, the 2.0R CRDi Limited, like our 2020 long-termer; pretty much the same car, just a different engine in each case.
So yes, we’ve chosen a high-end petrol model, but that gives us the closest match in performance (130kW/265Nm petrol vs 136kW/400Nm diesel) and the 1.6T is still $4000 cheaper than the CRDi at $59,990.
The 1.6T averages 7.7l/100km compared with 6.4l for the CRDi. With a sample 95-octane petrol price of $2.23 at the time of writing, that means it will cost about $172 to drive the 1.6T 1000km.
At $1.35 per litre for diesel, the same distance in the CRDi will cost just $86 in fuel, but you have to add $76 per 100km for RUC. Grand total: $162. So you’re only saving $10 per 1000km (or less if the petrol car is running regular fuel), which means a lot of driving to make it work price-wise.
There’s a school of thought that says diesel SUVs have higher residual values than petrol, so that price difference might be irrelevant anyway. You can also factor in the convenience of going so much further on a tank with diesel and many people prefer the driving characteristics of diesel, especially on a journey.
Diesel service intervals are sometimes longer, but then the cost of those services can be higher. It all depends on the vehicle in question.
That flat-fee RUC of $76 is the reason diesel small cars don’t make sense in New Zealand. Because you’re paying by distance rather than fuel consumed, it’s costing proportionally more in RUC for a really thrifty vehicle than a thirstier one. In economic terms, we’d argue it’s really only worth considering diesel in a medium-sized car or SUV (like the Tucson) or larger.
The rise of hybrid power is one further complication in the argument. There’s not a huge amount of choice in this genre, but if we compare a Toyota RAV4 Hybrid with the Tucson, the case for petrol looks very strong: at 4.8l/100km, it would cost just $107 to drive the Toyota 1000km.
Which is really cleaner?
Diesel gets a bad rap for being more of a health and environmental hazard than petrol. That’s somewhat justified with older vehicles, but not so much with newer models.
Diesels produce less greenhouse gas per-kilometre than petrol cars. But diesels also produce higher levels of fine particulates, which present a health risk as they can enter the lungs. However, modern diesels with particulate filters eliminate most of this matter.
Petrol engines produce more smog-forming Nitrous Oxide (NOx) over time and higher HydroCarbon (HC) emissions, which are highly carcinogenic.
The point is, it’s not as simple as petrol being clean and diesel being dirty.
Broadly speaking, as there are some many variables, smaller cars are better with petrol, larger ones better with diesel, with that middle ground populated by options to suit each buyer’s specific needs and preferences.