A litre of motor oil has a lot more than oil in it

Wheels contributor Gerry Malloy spells out what's in a litre of motor oil - and it's not all oil.

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It may be thicker or thinner, its odour may vary a little, and there might be some slight difference in colour. But for the most part, for most of us, oil is just that. Oil.

That’s not the case when it comes to the stuff we put in our engines, however. Today’s engine oils are hugely complex chemical blends, specifically designed to perform a multitude of functions says Mark Ferner, an engineer at Shell’s research laboratories in Houston, Tex.

Ferner made a presentation on the subject to jurors for AJAC’s Best New Technology Awards and other interested members at last week’s annual Canadian Car of the Year TestFest in Niagara-on-the-Lake.

More: Here's how to get $3,000 just by changing your oil

When we buy a litre of oil, only about 75 per cent of what’s in the bottle is actually oil, he told us. And that’s a good thing.

The other 25 per cent is typically a mix of additive packages that help the oil perform a laundry list of functions. Without them, the best of today’s oils would be wholly inadequate for the demands that modern engines place upon them.

Oil’s primary role is to lubricate, of course, allowing moving surfaces to slide smoothly past each other and preventing or minimizing wear.

But it also acts as a coolant — much of an engine’s waste heat is transferred into the oil — and as a sealant, ensuring that the piston rings do their job of keeping compression and combustion pressures within the combustion chamber.

Even the basic role of lubrication takes two forms, depending on where it is in the engine. In some cases, such as simple journal bearings, it forms a film between the surfaces on which each slides, preventing them from touching and sticking.

In other cases, it forms a chemical bond with the surface, creating a sacrificial coating that ultimately wears away, thus protecting the surface itself.

One of the biggest challenges oil has to overcome is temperature, or rather the dramatic range of temperatures over which it must function. It must both lubricate and flow during cold start-ups at –40oC (–40oF) or below and continue to do its job at hot spots within the engine that reach as high as 425oC (800oF), as well as every point in between.

Many of the additives within the oil are designed to help cope with those extremes. Plus, they perform such unheralded functions as preventing foaming of the oil, reducing or cleaning up carbon deposits and sludge formation, carrying wear particles in suspension until they can be filtered out and inhibiting rust formation on engine parts.

The only way you can determine how well an oil performs those functions is to look at what the industry calls the “Service Symbol Donut” label on its container.

It’s shaped like a donut, hence the moniker, and contains two important pieces of information: the API Service Classification (at the top) and the SAE Viscosity Grade (in the centre). Viscosity Grade is a subject unto itself, which we’ll discuss at another time.

The API (American Petroleum Institute) Service Classification is a two-letter code starting with either an “S” for gasoline engines or a “C” for diesel engines. The second letter speaks to the model years the engine oil was formulated to serve.

The first API service classification was “SA,” which designates oils designed to meet the requirements of cars built prior to 1930. As the test standards became more stringent, the designations changed progressively so the best oils currently available are labeled API SM.

You can determine the minimum quality recommendation for your vehicle by checking your owner’s manual.

Any oil with that or a later designation (a later letter in the alphabet) will be suitable. For example, if your owner’s manual recommends an oil designated SJ, then any oil designated SJ, SL or SM may be used.

You may also find an ILSAC requirement in your owner’s manual. ILSAC (International Lubricants Standardization and Approval Committee) is a body formed by several automakers in the 1990s, who wanted to add additional qualifications to engine oil specifications, beyond API.

Chief among them was a fuel-economy factor. As Ferner explained to us, improving certain oil characteristics can reduce fuel consumption by 1-to-2 per cent.

Oils that meet ILSAC’s fuel economy requirements typically have the term “Energy Conserving” at the bottom of the donut label. They may also display a separate label marked GF-3, GF-4 or GF-5 — the latter specified for 2011 and later models.

Bottom line: check your manual before changing oil to make sure it’s right for your vehicle.

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