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Home Motoring DIESEL or PETROL – Should you buy a petrol or diesel engined vehicle?
Diesel or Petrol

DIESEL or PETROL – Should you buy a petrol or diesel engined vehicle?

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Motoring Editorial published in the August 2016 edition of The Billboard:

PETROL ENGINES

Most people, as well as the average mechanic, are more familiar with petrol engines than with diesels. The good ones are robust, can tolerate a certain amount of abuse, and do not demand any particular driving style. I would not hesitate to buy a petrol-engined car or bakkie in spite of the fact that they use more fuel than diesels.

The addition of a turbocharger changes this happy picture. The extra complication inevitably increases the importance of regular servicing, but this should not deter you if you crave the extra power.

DIESEL ADVANTAGES

A diesel is more efficient, and therefore uses less fuel under the same driving conditions than a petrol engine would. In low-speed part-throttle conditions you can expect at least a 20 percent reduction in fuel consumption, but if you go faster the difference in consumption diminishes.

A diesel engine cannot rev up to much more than 4 000 revs. This has the advantage that the diesel doesn’t have to be revved to develop any useful torque (i.e. pulling power). Turbocharged diesel engines develop even more low-down torque with result that they’re a lot of fun to drive.  These engines should not be subjected full-throttle acceleration from low speed in a high gear. This is called lugging and tends to promote the kind of crankshaft vibration that causes extra stress to engine and transmission components. It’s better to change to a lower gear before accelerating

The ideal solution is to buy a diesel with an automatic gearbox. You will then always be in the correct gear. In fact, an automatic gearbox is an engine saver, and should always be preferred if somebody else is going to drive your vehicle.

DIESEL DISADVANTAGES

In earlier days, excessive noise and vibration would have been high on the list of undesirable features but modern diesels are extremely quiet due to major advances in controlling the combustion process.

Diesel engines generally need more frequent servicing. The combustion process produces more carbon particles than a petrol engine so that the oil usually gets dirty quicker, and have to be changed more frequently. During combustion fuel particles are surrounded by at least 20 percent excess air. If this percentage is reduced by (for example) a dirty air filter the engine will overheat and this may cause permanent damage.

Diesel engined vehicles are usually, but not always, more expensive to buy with the result that it can easily take you many years to make-up the price difference by means of what you save in fuel cost.

NATURAL ASPIRATION OR TURBOCHARGING?

To me, a naturally aspirated-engine is like a tame workhorse, but a turbocharged engine is more like a pedigreed racehorse. In the past, most diesel engines used to last longer than petrol engines because of the robust construction, but that is no longer true. The addition of a turbocharger has changed this perception, but sensible driving habits and proper servicing will promote a long component life.

Text supplied by Jake Venter

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