Petrol or Diesel – The Debate of the Century

Until a few short years ago, there was compelling argument to rather opt for a diesel car than a petrol one because diesel had the consumption advantage by a country mile (and the fuel was cheaper than petrol). This is no longer the case, necessarily. Additionally, the argument that diesel engines were often noisy and smoky also does not hold much water anymore, as modern diesels are very refined machines.

Diesels used to feel much more powerful underfoot because of the vast amounts of torque available at low engine speeds (that is the Nm figure in the engine output rating – for instance, a new Toyota Hilux 2.8 GD manual has a specified output of 130kW and 420Nm of torque).

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The higher the number, the better the performance. In a diesel, the torque figure is often quite high as most of these engines are boosted by a turbo – this is that fact that makes it so enjoyable to drive!

Because of increased environmental pressure from governments on the automotive industry as a soft target for pollution taxes (an easy & convenient cow to milk), automakers are forced to make every new engine series as efficient as possible on the power versus consumption table. While in the past petrol engines were mostly normally aspirated (no turbo), this has changed virtually overnight. Better engine efficiency was achieved by downsizing capacity and adding a turbo (or sometimes two).

With this came more torque lower down the engine speed range, making a modern turbo-blown petrol engine as much fun to drive as a blown diesel and providing much the same or even more power. By way of example, the Ford three-cylinder blown 1.0 EcoBoost engine as found in the Fiesta replaced the normally aspirated 1.6 that preceded it. Many examples from other manufacturers exist, and it may prompt you to ask the question: when last did you see a car’s engine size advertised on the back? Even in cases where you do see numbers on the boot, it does not always reflect what’s under the bonnet – a Mercedes C300 is powered by a blown 2.0-littre petrol engine and Merc CLA200 by a 1.6-litre.

One result of the downsizing of petrol engines was that emissions were lowered by a huge margin, making petrol versions today somewhat cleaner than diesels, which has not yet undergone the same revolutionary redesign.

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Because South Africa has comparatively dirty diesel when measured against European benchmarks (most diesel engines run on diesel fuel with a 500ppm rating, though many manufacturers specify 50ppm because of the sensitivity of the pollution-controlling catalytic converters; these scrub the most harmful emissions from the exhaust system), service intervals are set closer than on cars with petrol engines – typically 10 000km for a diesel, while petrol cars can often go 15-30 000km between servicing, depending on the lubricants used. This makes servicing of a diesel car typically more expensive than a petrol one over a distance of, say, 100 000km.

In the past, diesel fuel per litre was vastly less expensive than petrol, though pricing fluctuates from month to month and the advantage has largely been eroded.

New diesel cars are typically priced higher than the equivalent petrol model in a range, and this also reflects in second-hand values. One reason is that diesel engines, because they run at lower engines speeds and are considered to take less stress, are deemed to be more reliable and enduring in the long run than a petrol (one often hears stories of diesel cars with unusually high mileage and still going strong).

When juggling between a petrol or diesel choice of the same model car, consider the following:

  • The mileage you intend to cover in this car (i.e how long do you intend to keep it?)
  • What are the official fuel consumption figures for both?
  • Come resale, which will have the better value?
  • How much servicing will the car require, and at what intervals?
  • Phone a dealer and ask what a typical service for that model would cost.
  • Compare insurance costs – you may be surprised how much it could differ.
  • Take a drive. Petrol and diesel often require vastly different driving style in terms of gear changes etc. Be honest at which one gives you the most driving pleasure, and go with the one that weighs in the most positive balance of the factors noted above.


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