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I seem to recall that older diesel engines worked well when being used constantly, and not so well if used only occasionally.

If I am correct in my recollection, do modern diesel engines behave in the same way?


From the "Ask Jack" archives - 20 October 2009


I believe you could use that theory for both petrol and diesel engines. The best economy and least amount of wear takes place when an engine is at its optimum operating temperature. Oil circulation for example is vital to an engines life, and on a cold engine oil does not flow as quickly to lubricate key moving parts especially those furthest away from the oil pump such as camshafts on modern engines.

I understand where you are coming from however, the older diesels were used in a lot of commercial business operations because of their economy and high work rate. Because they are not high revving engines they would happily idle away all day and go for ever.

The huge reduction of sulphur in our fuel in recent years has seen the rapid introduction of the modern common rail diesel engine which is ideally suited for the traditional fleet from the 4WD's to the large, mid size and small cars. These engines, like petrol, have the ability to warm up very quickly and can be operated in a variety of environments without any undue affects. While they still have huge low down torque, the modern diesel is now capable of impressive performance across a much bigger vehicle speed and engine rev range.

In many cases the diesel service intervals are identical to the petrol variants also depending on the conditions they are being driven in. Particulate filters have also reduced the amount of soot produced from at the tail pipe and because they are more economical, the CO2 emissions are lower than petrol.

Are they cost effective in comparison to petrol is another question? Servicing is sometimes more expensive, you pay a higher annual registration fee as well as Road User Charges (Approx $36 per 1000km plus an administration charge of around $10). Add to that the cost to purchase some diesel vehicles is often several thousand dollars dearer than a petrol. For some motorists who travel less than say 20,000km per year a fuel efficient petrol vehicle is still a better option.

Certainly if towing a heavy load on a regular is a high priority then a modern diesel is very hard to beat.

Mnay of the older diesels are getting past their used by date and you would not want to purchase one and have to spend money on a engine overhaul. The cost is often three times that of a petrol engine.