Motor oil is essential to the overall health and functionality of your car. This makes picking the right oil extremely important. Let’s go over how engine oils are classified, the difference between conventional and synthetic oils, and whether it’s safe to mix oils.
Conventional vs. Synthetic Oil Change
Oil Viscosity Ratings
The most important thing to consider when picking a motor oil is viscosity. Viscosity determines how easily an oil pours at a specific temperature.
Two numbers are used to classify oil viscosity. Here’s an example: 5W-30. “W” stands for “winter.” The first number refers to how the oil flows when cold (e.g., when you first start your engine.) The second number refers to how the oil flows at normal engine operating temperatures (measured at 100°C.)
The lower the number, the thinner / less viscous the oil, and the easier it’ll flow. For example, let’s compare a 5W-30 oil and a 10W-20 oil. The 5W-30 oil will flow faster at engine start-up, but slower than the 10W-20 oil once the engine reaches operating temperature.
The most common engine oil ratings are 5W-30, 5W-40, 10W-30, and 10W-40. If you live somewhere with extremely low temperatures, go for a 0W-20, 0W-30, or 0W-40 oil.
Viscosity index (VI) is another crucial part of choosing the right oil for your car. Oil VI determines how much the viscosity of an oil changes when the temperature changes. If an oil’s viscosity doesn’t change much between 40°C and 100°C, it’ll have a higher VI.
Most conventional oils will have a VI between 95-100. Highly refined oils typically receive a score of 120 and synthetic oils can go up to 140. The higher the number, the higher the VI, and the less change in viscosity.
Conventional Oil
Conventional, or regular, oil is usually thinner than synthetic oil and is best for cars made before 1990. It’s cheaper than synthetic oil and can offer you improved fuel efficiency and reduced emissions.
When temperatures rise, however, conventional oils may become too thin to protect your engine. This can lead your engine’s components to wear out and cause inefficient oil pressure. Because it burns faster, you’ll also have to replenish conventional oil more than synthetic.
Synthetic Oil
Synthetic engine oils have a naturally higher VI than regular oils. They’re more expensive than conventional oils, but offer many benefits, including:
- Handling extreme temperatures
- Standing up to intense driving conditions (e.g., towing heavy loads)
- Offering longer intervals between oil changes
- Protecting your engine better
Synthetic oils are ideal for most modern cars and diesel engines. Using synthetic oil in an older car, especially one with high mileage, can cause leaks that force the engine to burn more oil and lead you to have to replenish the oil more often.
Is It Safe to Mix Oils?
As long as you’ve confirmed your car can handle it, it’s safe to occasionally mix/switch between regular and synthetic oil. However, conventional oil will dilute the protective benefits that synthetic oil offers. Therefore, it’s not ideal to regularly mix oils. Only do this in an emergency or if you’re switching from one type to the other.
DIY Oil Change
Whether you use synthetic or conventional oil, the method for doing an oil change remains the same. To learn how to do an oil change from home, check out this guide.
At NAPA, we offer a wide range of motor oils to choose from. If you have any questions about choosing the right oil for your vehicle, visit a NAPA Auto Parts store to get an expert’s opinion.
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2 Comments 
When using synthetic oil, what if any down side is there to using different brands .
Hello ,
Mixing different synthetic oil brands can lead to incompatibility issues, varying performance levels, and potential warranty concerns. To ensure optimal performance, follow your vehicle’s manual for recommended oil specifications.