8/3/2023 0 Comments Motor oil grades explainedStart by checking your owner’s manual or the car maker’s website. To get to these really low ‘W’ ratings needs the precise chemical formulations of fully synthetic oil. Regular mineral oils can only adapt so far. It’s not uncommon for makers now to specify a 5W 30 motor oil even for a regular family car. Modern engines have much finer tolerances and need much better low-temperature performance. To measure this, a second low-temperature ‘winter’ (W) test is added, so you might get SAE 20W 50 multigrade oil, for example.īasically, the lower the ‘W’ number, the better the cold performance and the higher the second number, the better the oil copes with high temperatures.īut SAE 20W 50 motor oils are old-school, and engine tech has moved on. The solution is ‘multigrade’ oils which use VII additives (Viscosity Index Improvers) to make the oil run more freely at low temperatures. An oil designed for normal engine operating temperatures is much too thick when the engine is cold, which has traditionally been when most engine wear happens. This gives an standardised SAE (Society of Automotive Engineers) rating so, for example, a relatively thick, old-fashioned motor oil might have a viscosity of SAE 50.īut car engines operate across a range of temperatures, particularly when they start up ‘cold’. The technical term is ‘viscosity’ and it’s traditionally been measured at 100 degrees Centigrade. Much modern engine technology has only become possible because oils have been developed to support it.įor oil to offer the right protection and performance it has to ‘flow’ properly through and around the engine components. So it sounds as if mineral oil comes from the ground and synthetic oil comes from a laboratory, but in fact they’re both products of crude oil and it’s just that synthetic oils offer a step-change in sophistication, performance and, alas, expense. ‘Part-synthetic’ oils lies somewhere in the middle, offering much of the performance of fully synthetic oils but at a much lower cost. Synthetic oil can be made more durable, particularly for the ‘shear’ stresses in transmission systems, and allows lower SAE ‘W’ grades for better performance and protection at low temperatures. The difference is that its molecular structure and properties are modified, refined and ‘synthesised’ using complex laboratory processes. Despite the name, though, synthetic oil is still derived from the thick black stuff ejected by oil wells. ‘Synthetic’ motor oil is the pinnacle of engine lubrication for high-performance vehicles. It’s ‘cruder’ than synthetic oil, but also a lot cheaper to manufacturer, and it can still provide perfectly adequate protection for less demanding engines. ‘Mineral’ oil sounds like it should be synthetic too (minerals aren’t organic, after all), but the name comes from the way it’s extracted from the earth like other mineral deposits. So here’s a guide to engine oil types, standards and jargon to help you hack your way through this oily jungle An old car engine might be perfectly happy with a few good glugs of old-fashioned SAE 20W 50 mineral oil, but engine technology has moved on and the demands on engine oils have moved on too. Modern car engines use extremely fine tolerances and subject oils to a series of very different forces, conditions and stresses. But maybe it’s not the cost of the oil that’s putting you off but the difficulty of finding the right one?īuying oil isn’t so simple any more. Oil isn’t cheap, but it’s a lot cheaper than a premature engine replacement. The chemical degradation comes from the accumulation of contaminants from engine combustion processes and leaky gaskets and oil seals (in older cars), and the effects of oxidation. The mechanical stresses and strains are probably easy to picture and lead to steady molecular breakdown. Your engine might be purring like a cat, but inside it the oil is being subjected to constant mechanical and chemical stresses that will slowly degrade its performance. It’s also vital to change the engine oil at the manufacturer’s specified service intervals, because oil wears out. It’s not just about keeping the oil level topped up. That would mean a LOT of expense and trouble – far more than the cost of a litre of oil at the gas station and a dipstick check every weekend. If you don’t maintain your car’s minimum oil level, there’s a good chance key engine components will be starved of oil and either wear prematurely or fail catastrophically. And the older your engine, the more oil it will tend to use (or leak) and the more often you need to check the dipstick to make sure it stays above the minimum level. Even if your car is relatively new and you take it to a dealer for servicing, you still need to check the oil level.
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