Motor oil for your car: what you need to know

Motor oil is basically the lifeblood of your car’s engine. It serves as lubricant for all wearing surfaces, and without it, your engine will seize and be permanently damaged, if not destroyed.

As important as oil is, equally important is the type of oil you use. There are several different types, and you have to use the right type for your car. If you use the wrong one, it won’t work at full effectiveness, it may cause leaks, and it could ultimately shorten the life of your engine.

Your car’s owner’s manual will tell you which type of oil to use; if you don’t have one, you can check with a dealership to make sure you use the right kind.

hand pouring oil into a car engine.

Why are there so many different types of motor oil?

The primary variable in different types of motor oil is viscosity, and it’s one of the main reasons there are so many different varieties. Temperature, application, and conditions all affect the need for more or less viscosity. (Viscosity refers to a fluid’s tendency to maintain its shape, or, basically, how thick it is. The lower the viscosity, the faster a fluid will flow).

What do the numbers and letters on motor oil mean?

When you see a ‘W’ in the motor oil type, that stands for ‘winter’—it refers to how the oil will perform in cold weather operation, and tells you that this oil is suitable for winter use. The number in front of it is the ‘weight’ and refers to how viscous the oil will be at 0 degrees Fahrenheit; the higher the number, the more viscous it will be. 

The second number refers to the viscosity at the higher end of the temperature range. So an oil that is rated SAE 10W-30 will have a viscosity of 10 weight oil when cold, and of a 30 weight oil when hot. 

What does ‘SAE’ mean?

SAE stands for ‘Society of Automotive Engineering’, and it simply refers to the entity that developed the oil measurement rating system. (SAE also sets many other standards for other automotive measures and ratings systems.) In the context of motor oil, the ‘SAE’ designation refers to the viscosity.

Monograde vs Multigrade

Monograde (or single grade) oil has just one viscosity, and it doesn’t change according to temperature. As a result, it has very limited applications. You really don’t want to use it in a car engine because with a car you need an oil that can be less viscous when the engine is very cold, and then thicken up as it heats up. 

That’s why, for a car, you need a multigrade oil, which is designed to flow differently when the engine is cold than when it’s warm. They’re always labeled with a range (like 10W-30) that refers to its lowest and highest viscosity for the range of engine temperatures. This protects the engine much more effectively than an oil that has just one viscosity.

Which oil should I use for my car?

The most important thing is to use the type of oil that’s recommended by your car’s manufacturer—it will be very specific about synthetic, conventional, or blend, as well as rating. You can find that information in your owner’s manual, and often on the car’s oil reservoir cap. If you don’t have access to either of those things, looking it up online or calling your dealer are both good bets.

Once you know what type of oil to use, changing your own oil at home is a relatively simple task. You’ll save money, and can be a rewarding DIY project. Check out our guide on how to change your oil, along with several other bits of maintenance that are easy to perform yourself.

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