Originally Posted by
JDNSW
Diesel is, as you say, generally about 10c/l more expensive than petrol, or in current terms round here about 6% more expensive. However, while it is not possible to be exact, as there is rarely a direct comparison, the fuel economy of diesels is usually more like 30-50% less than the same vehicle with a petrol engine, so on fuel costs, you are way ahead. The difference in initial cost can be quite significant, but this is usually offset by the difference in depreciation (see for example the current difference in second hand prices between petrol and diesel Discoveries), and remember that depreciation is almost always by far the greatest cost of owning/running a vehicle. There are other advantages to diesel over petrol engines apart from fuel costs, these include longer range, usually longer before engine overhaul, usually greater reliability and lower maintenance, and safer fuel handling and more readily available fuel away from towns.
Having said all the above, by far the cheapest fuel is LPG, but this is a unique Australian position due to an unusual excise situation, which may change at any time at the stroke of a pen (well, it may take an act of parliament). This is offset by the cost of conversion (payback is around a year in most circumstances), often the loss of interior or luggage space, loss of range with the added problem of inability to readily carry extra fuel and the rarity of LPG supply points away from the major centres.
From a purely theoretical point of view, it can be expected that diesels will always win out in the fuel consumption stakes as the energy efficiency of the engine is always greater simply because of the higher compression ratio - which will always be much higher than petrol engines. Whether this translates into cheaper running costs depends on a host of variables, as indicated above. The comments made by the Ford VP may apply to Ford passenger cars in the unique situation of Ford as a company, but I would suggest that he look at his sales of light commercials, where costs are taken into account much more than in car sales, and I suspect he will find that there is a majority of diesels sold. His comments may have more to do with the fact that Ford does not have a suitable diesel that would suit the Falcon and cost any where near the current engines to produce. From their point of view LPG would make a lot more sense.
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