What Is the Difference Between 5-30 & 20-50 Motor Oil?

by Devette McDowell
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Using the proper oil for your vehicle is an important part of good maintenance. Motor oil is used to lubricate an engine’s moving parts while keeping them cool, clean and inhibiting corrosion. The owner’s manual typically states which oil is best for a vehicle under normal weather and driving conditions. You should also consider such variables as climate and the age of the vehicle when choosing the right motor oil. Motor oil grades 5W-30 and 20W-50 are very different. Understanding their differences can help you determine what motor oil is best for your vehicle.

Motor Oil Viscosity

Motor oil is issued an index rating by SAE (Society of Automotive Engineers). This rating consists of two numbers based on the oil's viscosity when at a cold and warm temperature, respectively. Generally, the higher the number, the more resistant the oil is to flow. Common ratings range from 5W to 60. The first viscosity number appears before the "W” (which stands for Winter). It represents the oil's rating in a cold climate. For example, 20W is thicker than 5W before the engine is started. The second number indicates the viscosity rating of the oil when the engine reaches operating temperature. This means that the 20W-50 is more viscous than the 5W-30 motor oil once the engine reaches the proper temperature for driving. The more resistant the motor oil is to thinning as it heats up, the higher its second number. Thicker oil generally lubricates engine parts better than thinner oil.

Viscosity and Temperature

Low-viscosity motor oils are preferable in cold climates because they are thinner and flow easier in extremely cold temperatures. A vehicle using high-viscosity oil may have trouble starting up in extremely cold weather. Conversely, high-viscosity oils are preferable in warmer climates. The density protects the engine’s parts and improves a vehicle’s overall performance.

5W-30 Motor Oil

5W-30 oil is best for vehicles that are regularly driven in colder climates where temperatures can fall below 0 degrees Fahrenheit. It is a light oil that will circulate through an engine faster than a more dense grade. 5W-30 is designed for use in colder climates where cold engine starts are common. It is generally recommended for new and high-mileage vehicles under all weather conditions.

20W-50 Motor Oil

Due to its high-viscosity, 20W-50 is suitable for hotter climates. It is highly recommended for older vehicles. The oil's density helps protect aging engine parts and helps prevent leaks that are common with older cars. It is important to note that 20W-50 oil may be too thick for many newer passenger cars and can cause serious engine damage. Check with an automotive professional before switching motor oils.

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