Car care: understanding engine oils

[Article copyright by Ewe Paik Leong]

Every time a mechanic asks a motorist to select engine oil, he often chooses on the basis of price alone. Many motorists, after years of owning a vehicle, don’t understand the technical ratings used to describe different oils.

Take two examples: 10W 40API SM/CF and API SM/CF SAE 20W50. The API rating of an oil is the translation of the technical jargon of the American Society of Automotive Engineers (SAE) and the American Society of Testing & Materials. The SAE rating indicates the viscosity of the oil at different temperatures. (The term viscosity refers to how well the oil will flow.) A 10W-40 oil protects like a 10 weight oil when cold; like a 40 weight oil when hot. Straight 20W (or 40W) oil, however, is designed to have constant viscosity. This means the oil is designed to flow and protect like a 20W when hot or cold.

The alphabet of the S in SM means that the oil is meant for a petrol engine. The M refers to the level of the rating. Oils with SA, SB, SC, SD are obsolete. Currently, oils are rated SG, SH, SJ, SL and SM, with SG being the lowest rating and SM the highest. Sometimes the SM rating is followed by a slash (or sometimes a dash) then by a CD, CE, CF, CG, CG4, CH or CI4 – these are all diesel engine ratings.
The highest rating is CI4, and CA, CB and CC have gone to the days of the dinosaur.

Engine oils are of three types: petroleum-based (refined from crude oil), synthetic (manufactured in the laboratory) and semi-synthetic. The biggest disadvantage of petroleum-based engine oil is that it breaks down during high temperatures and forms sludge. The drawback of synthetic oil is its higher price compared to petroleum-based engine oil. To derive the maximum benefit of using engine oil, you should change it and its filter according to manufacturer’s schedule. This may be as often as 5,000 kilometres or every three months.

Let’s look at the functions performed by engine oil. First, oil lubricates the moving parts of the engine to reduce wear and tear. As 90% of all engine wear takes place within the first ten seconds of a cold engine start-up, the importance of using quality engine oil cannot be over-stressed. Second, the oil acts as a protective film between the pistons, rings and cylinders. Third, oil also cools the engine and buffers against the noise of moving parts. Finally, it also flushes metal particles from the bearings of the engine.

So, the choice is yours: sewing machine oil or quality engine oil. Having said that, beware of marketing gimmicks. I recall writing brochures for a client in Kepong which exports its engine oil to China, and they asked to jazz up their products with all kinds of unsubstantiated claims.

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