Motoring: Facts on oil
IT'S ONE OF THE stranger facts about motoring in Irelland that many dealers don't stock the type of oil reecommended by their own manufacturers. This means that your car, which may run best on (say) Castrol GTX 20W-50, could receive instead a transfusion of Shell Super at its regular service. Now, Shell Super is an excellent oil but it may not be right for your car.
An example: Peugeot's handbooks for their 104 and 304 models explicitly reecommend a particular oil in the following terms: "Only Esso lubricants should be used for the lubrication of your Peugeot. These lubriccants have been subjected to numerous tests and are perrfectly suitable for your car and will not cause corrosive action on the alloys used in the manufacture of Peugeot cars. "
In spite of this unequiivocal advice only one of five Peugeot garages contacted by Magill even stocks Esso! One recommended Castrol GTX, another Shell multiigrade which was, we were told, "equivalent to Esso", and the last three also stockked Shell because of dealerrship obligations. "Anyway", one mechanic said, "Shell's just the same. You can use anything you like."
If this were so, car-owners wouldn't need to worry what kind of oil is used to lubricate the engine. In fact, the variious brands contain different additives, and therefore different properties. Some are more suitable for your engine than others. (Although Peugeot was taken as an entirely random example, the story is similar with other makes.)
Duckhams Oil Company has undertaken chemical tests on thirteen different engine oils and found that no fewer than eight of them failed to meet British Leyland's reequirements for lowature viscosity (the "anti-flow" property of an oil); one fell below the standards set by the Ford Motor Company; still another conntained no zinc, which is essential to prevent engine wear.
Why is the type of oil your garage uses important? The answer is that the engine's life expectancy hinges to a large extent on satisfactory lubrication, which implies the use of a high-quality oil. It's widely believed that an oil merely reduces friction and hence wear and tear. In fact, it achieves a great deal more. Oil helps seal the tiny gap between piston and cylinder which prevents leakage of high-pressure gases after commbustion, helps remove exxcessive heat, the development of "hot" areas, reduces corrosion and absorbs some of the potentially damaging waste products of combusttion.
An oil, therefore, has to be developed to satisfy exacting . requirements. In the last few years oil technology has made giant strides. For instance, before the introduction of multigrade (which can be used over a wide range of outside temperatures) it was usual to use two different grades in a year's driving - one for summer, the other for winter. This was because oils are affected by temperature changes, tending to thin out when hot and thicken when cold.
In the old days before the advent of multigrade mixxtures a thick summer oil was like tar before it heated up. An additive (known as viscous, long-chain polymers) turns multigrade into a yearrround oil by reducing its tendency to thin out when hot and thicken when cold. Thus the designation SAE 20-50 means the oil combines the viscosity qualities of an SAE 20 (winter) oil and SAE 50 (summer) oil.
The latest development is the so-called synthetic oil (as compared to conventional mineral oils) which is more expensive but, according to independent research, more efficient. The new wonder oil, if you can believe the manufacturers, is supposed to shield the engine's moving parts with a film of ideal thickness regardless of temmperature, provide easier startting (hence less battery wear) because even very low temmperatures hardly affect the synthetic oil's viscosity, reeduce oil consumption by about 40 per cent, and maintain high oil pressure whether at low or high rpm.
Is synthetic oil worth about four times the (bulk) cost of conventional oil? Yes, provided you can get it since it's on sale only in very few outlets in Ireland. The cost of oil is low relative to the total cost of driving and car maintenance, whereas the percentage effects of a top-quality oil are SUbstantially higher, as we've explained.
FOOTNOTE: Magill has discovered a perfectly legitiimate way of substantially reducing your car's service costs: Bring your own oil. Here's why. Almost all garages charge the retail rate of about 50p a pint when they change your engine's oil. Now, if you buy your, own oil in a bulk five-litre can, the saving works out at roughly 40 per cent, with the added advantage that you can choose the oil that goes into your engine. Doesn't matter if the garage is a "Shell station" or whatever; mechhanics are obliged to use the oil you provide. Take Maxol 20W-50 as an example. Price per pint is 50p, which would cost £3.52p for a fairly standard four-litre oil change. But bring-your-own oil costs just £2.11 - that's a saving of £1.41.
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Oil Language: What does SAE mean?
SAE stands for the initials of the Society of Automobile Engineers in America which developed an oil's viscosity classification.
What is viscosity? It's a property of fluids by which they resist flow. A thin freeeflowing oil has a low viscosity and a thick, slow-flowing oil has a high viscosity. Thereefore, the friction created in a moving part depends to an extend on the oil's viscosity.
What are additives? They are properties added to the base oil to improve its perrformance. Among other things, they reduce the rate at which undesirable changes take place in the oil during its service life. For example, "ashless dispersants" are used to keep the engine clean under hot conditions and to prevent the formation of cold sludge in winter; "corrrosion inhibitors" do just that - prevent rust; "deterrgents" (not the household variety) are used to neutrallise harmful by-products of combustion.