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The letters SAE on a bottle of motor oil stand for Society of Automotive Engineers. (iStockphoto)
The letters SAE on a bottle of motor oil stand for Society of Automotive Engineers. (iStockphoto)

You & Your Car

Oil, by the numbers (and letters) Add to ...

When I took my car in for service the other day, I happened to notice the plastic container for the oil they were changing. What the heck are all those letters and numbers? – Brad

There is a wealth of information on that little plastic bottle.

The most prominent one is likely SAE, which stands for the Society of Automotive Engineers, an internationally recognized body that sets the standards for a great many things related to the automobile. You will also see API, which stands for the American Petroleum Institute, which is composed of most major U.S. oil companies. There are other national and international ones but you probably won’t see them here. The API sets the standards for motor oil in North America and that label or doughnut as it is often referred to contains the most significant information.

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The first part is a letter: S for gasoline engine use and C for diesel.

The second letter refers to quality: the higher the better. SH, SG and SF are old standards, now considered obsolescent. They were followed by SJ for 2001 and older engines, SL (2004 and older) and until a couple of months ago, SM. The very latest generation of oils have the SN rating, which promise better wear and fuel efficiency as well as longer change intervals – up to 16,000 km for some Ford vehicles. They may also be designated GF-5 or Dexos 1 (a GM proprietary rating).

The rest of those numbers and letters advise you of the viscosity or thickness of the oil. These ratings are established by the SAE.

Old engines and small ones like those used in lawn mowers and the like often use single viscosity oils. But the complexity of engines used in motor vehicles led to the development of multi-grade oils; for example, SAE 5W-30, which has the resistance to flow or viscosity of a lighter or thinner “5W” weight oil – W stands for winter – in cold conditions and 30-weight oil when the engine heats up.

Finally, at the bottom of that API label, you may find a phrase indicating the oil is “Energy Conserving,” meaning it has additional additives to reduce friction.

Diesel choices

Why don’t we get all those really neat diesel engines Mercedes, Audi and BMW sell in Europe. Are they afraid to bring them here? Don’t they make any money off them? – Bruce

I wish it were that simple. I suspect the companies would love to bring diesels here and help lower their corporate average fuel economy (CAFE) ratings. They are being pushed hard by these standards and could sure use the diesel numbers.

But there are two big hurdles: Americans don’t buy diesels and we still have dirty fuel.

The American market is huge in relation to ours – there are four or five states where they buy more passenger vehicles than in all of Canada – that manufacturers try to amortize manufacturing and distribution costs by bringing similar cars to the two markets. There are some exceptions. But rarely when it comes to vehicles that require separate emission or crash testing and the related massive additional costs.

The American resistance to diesels might well date back to that terrible period when General Motors tried to convert a gas engine into a diesel in Oldsmobiles with awful results. Or it could be the noise, smell and smoke of old diesels. Whatever the case, diesel sales have languished. Volkswagen and Mercedes have had some success with the new generation of clean diesels and BMW has joined the party very recently – but the numbers are small.

The biggest hurdle though is the quality of diesel fuel and the fact it remains heavily taxed and does not have the price advantage it enjoys elsewhere in the world. Even the most recent “clean” diesel available across North America contains a lot more harmful sulphur than the most recent generation of ultra-clean diesels available in Europe.

That extra sulphur in our diesel fuel will foul and destroy much of the intricate and expensive sensors and systems used in the latest-generation diesels offered in Europe.

Do you have car maintenance or repair questions? Send them to Globe Drive.

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