The price of driving: Diesel vs. Petrol

Whenever the global price of oil fluctuates, so the debate about choice of fuel rises to the surface like a hardy perennial. It’s a question that vexes all who are in the market for a new car and the answer will always depend on the perceived use of the vehicle. essentially, the choice comes down to the distance to be travelled over the course of a year. It is generally thought that if annual mileage exceeds 10,000 then a diesel will be the more cost-effective choice. Below that and buyers will be directed towards frugal petrol engines. Fuel economy is a major consideration when buying a car. To complicate the issue, however, the correct choice is also dependent on the owner’s specific circumstances and driving style. Furthermore, especially if driving is seen as something to be enjoyed
rather than just a chore, the characteristics of petrol or diesel engines comes into play. In short, what are they like to drive? I have had the opportunity to road-test a pair of Q3s, one a 2.0-litre TDI, the other a 1.4-litre TFSI. Despite the similarities of specification, including the excellent DSG automatic ‘box, the cars were almost identical to look at, yet very different in character. The 150 PS 1.4 TFSI engine is a unit tried and tested across the global vW brands. ‘Turbo fuel stratified injection’ combines petrol direct-injection with turbocharging. This system potentially delivers the same performance from a four-cylinder unit as would be expected from, say, a normallyaspirated v6 while using 10 to 15 per cent less fuel. On our test vehicle this was augmented by the relatively new, and optional,
‘cylinder-on-demand’ technology which, at low and medium loads, temporarily deactivates two of the four cylinders by closing their valves, thus saving a soupcon of the precious fluid. As soon as the driver accelerates, all cylinders cut in. It’s seamless and the only way you know that it is happening at all is because the dashboard tells you. The turbocharged direct-injection, TDI, or common-rail diesel engine is the latest in diesel fuel technology that offers extremely smooth and efficient combustion, along with reduced emissions thanks to particulate filters. It isn’t necessary to work this punchy engine hard to get good performance.

To aid economy, both cars came with Stop/Start. They look alike, their list of options is pretty much equal but, as ever, the diesel carries a purchase price penalty that is standard across the industry. Short of sitting at the roadside for hours with a calculator and a hotline to Stephen hawking, I can’t give you specifics on consumption and power, but I can confirm that, in terms of acceleration, both cars are similar in achieving the 0-62 mph sprint in under 10 seconds. Choose the more powerful 172 PS petrol variant and they will be neck-and-neck at the finishing post. We all drive differently, so the figures that work for me are likely to be better or worse depending upon how the car is driven. The diesel wins on consumption and is one group less in the tax bands, but there’s not a lot in it. The more miles you motor, the more the diesel makes sense, as you would expect, with over 50 mpg on the cards from an abstemiously deployed throttle. Out on the road is where you truly notice the difference. Sticking with the racehorse analogy, the 1.4 TFSI feels light and engaging, like a six furlong sprinter. To get the most from it, it pays to keep the revs up beyond 3000 when the mood comes on and the speed limit allows, giving the engine a rorty, sporty note under load. equally, the car is happy to potter about town making the most of that two-cylinder technology. The diesel, on the other hand, feels sturdy and heavier like a classy point-to-pointer, which, if you think about it, is exactly what you want when long distances need to be covered. rather than sprinting, the TDI eats the road with a powerful pull of torque. You can feel the extra weight through the steering. Both cars can engage the now ubiquitous ‘sport’ mode and can be driven using the gear-change paddles behind the steering wheel spokes. Depending on the model chosen, even emissions are close, with the petrol variants just taking the prize.

The Q3 has been with us for three years now and is proving to be a popular choice for empty-nesters and fledgling families. The vehicle strikes a good balance with carlike handling mixed with the versatility of the SUv. The boot is generous and there’s the usual legion of optional extras in terms of comfort, navigation, safety and high-tech electronics. These are the considerations that need to be thought through when buying any new car.
Crucially, then, buyers need to consider the petrol versus diesel argument very carefully. It is a lot of money to invest and making the wrong choice at showroom time means disappointment in the longer term. This is why buyers should road-test both versions thoroughly and consider the very different driving characteristics, bearing in mind the diesel/distance equation if economy is important. Conversely, there’s the current debatable backlash against the TDI engine within our major cities where the city-hall burgers have been convinced that diesel is the fuel of Satan. Whenever I am asked which is the best fuel to choose I always answer firmly and definitively, ‘it depends’. This takes us back to the beginning of this article. It really isn’t as simple as that. The petrol Q3 is fun, feisty and a pleasure to drive whereas the TDI felt solid, long-legged and capable of going the distance. Drive them both for some time, and don’t be sold on a quick turn around the block. Consider the pros and cons and look at your lifestyle and what is important to you. Get it right and the Q3 won’t let you down.