Auto Talk: All about oil

Do you change your own oil? These days, most people take their vehicle to a technician for routine oil changes. We trust service providers to use the right oil — because, let’s face it, many of us can’t tell the difference between 10W-30 and Cheez Whiz. Here’s a quick guide to what all those numbers mean.

API codes

The first thing to look for on an oil bottle is whether it’s for a gasoline or diesel engine, or okay for both. There will be some wording starting with “API.” This is the American Petroleum Institute rating. A code starting with S means the oil is for gasoline engines; C means diesel.

The second letter in each code indicates the level of protection. Each time the automotive industry upgrades its specifications for oil additives, the latest oil type is designated as the next letter of the alphabet. So, for example, SB is an older version than SC. You don’t have to choose an older version for an older car — “API SJ” means that the oil can be used in gasoline engines with any rating requirement from A through J.

SAE rating numbers

10W-50, 5W-30 … these are the numbers most people notice on an oil bottle. They indicate the oil’s viscosity (how thick it is). The lower the number, the thinner the oil. Oil with a rating of 10 is thinner and flows more easily than one with a rating of 30.

Oil gets thicker in cold weather and thinner when it’s hot. Picture the difference between solid and liquid honey, and the amount of effort it takes to spread each. If the oil is too thick, the engine might not work. If it’s too thin, it may not provide enough protection.

Oils with two different numbers in their rating are called multigrade oils. These show the different viscosity of the oil under hot and cold conditions. The W means winter, or cold weather. So, SAE 10W-30 means this oil is a 10 when it’s cold and a 30 when it’s hot. The SAE just stands for Society of Automotive Engineers.

Detergent oils

If you see a bottle of oil touting its detergent content, there’s no reason to choose it over another brand. The truth is that all multigrade oils are detergent oils. Some brands use this as a selling point, but it’s similar to bottled water promoting the fact that it’s non-fat. And it’s a myth that detergent oils cannot be used in older vehicles. They can and should be used in any vehicle that has an oil filter.

Synthetic or standard

Synthetic oils are thinner than standard oils. This means they provide better lubrication, but also leak or burn a little easier. If your engine is old and worn with existing leaks, you may want to choose a standard oil instead, but in general you can use standard or synthetic interchangeably in most vehicles.

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