Diesel Vs Petrol Engine: Which one is right for you? | Auto Expert John Cadogan

Diesel versus petrol. Which fuel is right for you? Don’t get this horribly wrong, because that’s going to cost you thousands.
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Diesel has so much going for it - it’s become incredibly popular. In the past 10 years, here in Australia, diesel sales have gone ballistic. Diesel SUVs - a four-fold sales increase in a decade. Diesel utes and light commercials - up more than double. Businesses, governments and private punters are equally enamoured of diesel.
For the record, I’m neither for nor against diesel. I’m certainly not some diesel evangelist, but nor do I hate it. Diesel is simply the right choice for some car buyers and it’s wrong for others.
There’s overlap in the middle, too. Meaning there’s a group of car buyers - of which you might be one - who could swing either way, happily. Let’s take the plunge.
Carmakers really don’t want you to dwell on what’s happening ‘down there’ under the hood. Just buy the damn car, would you? They’re really not in the ‘advice’ business. But diesel really is different down there.
Here’s what you need to know:
Diesel powertrains cost more up front - around $2500 more for, just for the engine, in mainstream vehicles. And it delivers better fuel economy. If we do a typical apples-for-apples comparison here, you can buy a Hyundai Tucson Active in petrol or diesel. They’re both 2.0-litre engines. The petrol drinks 23 per cent more fuel during the combined cycle lab test. That’s pretty typical.
The extra cost of the diesel is absolutely justified - the diesel engine is turbocharged, it has an extremely high-pressure fuel rail and a bunch of other hi-tech hardware - compared with the parts list for the typical alternative lo-tech petrol alternative - which is an atmo, multi-point injected dunger designed about 12 years ago. There are many exceptions. Like the Mazda CX-9 2.5 turbocharged direct injection engine - that’s an outstanding hi-tech petrol engine.
The diesel engine makes more torque - and therefore requires a beefier driveline in order to cope. Sometimes the petrol comes in 2WD, while the diesel is exclusively AWD - which also ramps up the cost.
Diesel is more fuel efficient - generally - for a few reasons. Mainly because the combustion process is more efficient. Reason being: diesel tolerates greater compression inside the engine. That allows it to expand over a greater range, and that gives you more efficiency. And, although the energy density of the fuels - per kilo - is about the same, diesel is a little denser than gasoline, so there’s a bit more energy in every litre of diesel.
The upshot is that if you can drive around 800 kilometres on a tank of petrol you’ll achieve more like 1000 kilometres on a tank of diesel - ballpark estimate. And that means, A) incremental savings over time, B) fewer overall refuelling stops, and C) you’ll enjoy more cruising range if you visit remote areas.
In those situations, when it’s a long way between refuelling stations, diesel can be a real plus.