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What Should I Consider When Buying Motor Oil?

Mary McMahon
By
Updated May 23, 2024
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Motor oil is a crucial component in engine care. The oil lubricates the moving parts of the engine, prolonging the life of the engine and making the car run more smoothly. However, as oil is used, it will start to degrade and collect grime. Therefore, it needs to be changed frequently: most automobile mechanics recommend that oil be changed every 3,000 miles (4,828 kilometers). When the oil is changed, the oil pan is completely drained and the oil filter is replaced before fresh motor oil is poured in.

Between oil changes, the motor oil may need to be refreshed occasionally. It is important to buy the same kind of motor oil that the mechanic used when the oil was changed: for example, if the mechanic put in 10W-40 oil, you should also use 10W-40 oil when you top off your oil. Therefore, you should think about what kind of motor oil you need when you are changing your motor oil, not picking up a quart to top off with. There are a number of things that you should consider when changing your motor oil, to ensure that your car will perform at a high standard for you for years to come.

The first thing to think about when buying motor oil is what type of oil you want to use. There are two bases of oil available: one uses petroleum, and the other is a synthetic. Petroleum based motor oil is cheaper, but also gives out faster and leaves more particulates in the engine. Synthetics are designed for high performance, and generally believed to be superior. They are also more expensive: if you do not engage in heavy driving, especially prolonged freeway driving, synthetics may not be necessary. Most mechanics also agree that motorists should avoid petroleum oils with additives in them, because the additives do not impact performance enough for the potential engine clogs to be worth it.

The second issue is the viscosity of the motor oil. Thin motor oil will tend to burn and break down at the high temperatures of an actively running engine. Therefore, a higher viscosity is needed so that the oil can stand up to high temperature use. However, high viscosity oil is too sluggish when a car is being started, and will not flow through the engine. Therefore, motor oil is manufactured in combined viscosities which behave differently at different temperatures. The viscosity level of oil is tested and determined by the Society of Automotive Engineers (SAE), and the SAE ratings are listed on bottles of motor oil in multiples of 10, and more rarely, five.

In hot weather, you will need oil motor oil of a higher viscosity, because the heat will interplay with the engine to have an impact on the oil. People living in hot areas or changing their oil before the summer should think about oils in the 10W-50 range: the “W” means that the oil is suitable for winter use as well. In cold weather, low viscosity oil is needed, because the cold will make the oil sluggish—10W-30 or 40 is more appropriate. For people in temperate climates, 10W-40 oil is ideal.

Several others things on the label of a bottle of motor oil will provide information about its quality: the flash point, percentage of sulfated ash, and percentage of zinc. The flash point refers to the point at which vapors rising from the oil will ignite: the higher the flash point, the better the oil quality. The percentage of sulfated ash refers to the detritus left behind as the oil is used: the lower this number, the better the oil. Finally, zinc protects the parts of your engine where there is metal to metal contact, but too much zinc can clog the engine: for most automobiles, the zinc percentage should hover around 0.1%.

WikiMotors is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WikiMotors researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
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