Synthetic vs. Conventional Oil: Which Is Better for Your Car? (2024)

When you took your car in for an oil change 60 years ago, you likely only had to choose between brands. If you aren't sure of the differences between synthetic and conventional oil, you might feel overwhelmed by all the blend and brand options.

Most manufacturers recommend conventional oil for most car models, but synthetic oil has advantages that may make it a better option depending on factors such as your vehicle's age and performance and your driving habits.

Read on to discover which type of oil is best for your car.

What Is Conventional Oil?

Conventional oil, also known as crude oil, exists organically in the earth's crust and is pulled from the ground using a drill and pump. Hydrogen and carbon make up the bulk of its composition, but it may also include traces of sulfur, nitrogen and metals. Manufacturers refine the crude oil and may add a few additives to improve performance, but conventional oil is mainly natural in composition.

The Pros and Cons of Conventional Oil

Conventional oil has been used since the invention of the first car, so it's withstood the test of time thanks to its many pros:

• Conventional oil is more affordable. Because it is less refined and processed than synthetic oil, it is cheaper to produce and thus cheaper for consumers looking to limit their ownership costs.
• Conventional oil is more readily available. Conventional oil is available at every repair shop. You won't need to shop around to find it.
• Conventional oil is better for older engines. Due to its higher viscosity (an oil's thickness and ability to flow), conventional oil flows more slowly through your engine, ensuring every part is lubricated. Older engines require more lubrication to keep things running smoothly and resist breakdown, so many mechanics recommend conventional oil for cars over 75,000 miles.
• Most manufacturers recommend conventional oil for most cars and driving conditions. Chances are, the dealership filled your car with conventional oil when you purchased it.

But conventional oil is not without its cons:

• Conventional oil may slightly lower your gas mileage. Because it lacks a consistent molecular size, conventional oil is thicker and less smooth than synthetic oil. As a result, your engine may have to work harder, resulting in lower gas mileage.
• Conventional oil is more susceptible to extreme temperatures. In the cold, it thickens, which means it takes longer to circulate. (This is why experts recommend warming up your engine before driving in the winter.) Conventional oil can evaporate and degrade in the heat, requiring more frequent oil changes to protect your engine.
• Conventional oil doesn't last as long as synthetic oil. As an organic product, conventional oil breaks down faster than synthetic oil. Experts recommend changing your conventional oil every 5,000 to 7,000 miles. Since you will need more oil changes over time, this may offset the cost savings of a conventional oil change.
• Conventional oil is less environmentally friendly. Since conventional oil can leach contaminants from the air, deposits can build up in your engine. These deposits can cause your engine to work harder and produce more emissions. Used oil is also toxic waste, so the increased frequency of oil changes produces more toxic waste.

What Is Synthetic Oil?

Unlike conventional oil, synthetic oil is mostly human-made. It consists mostly of synthetic chemicals, although the exact nature of the chemicals changes based on the manufacturer.

Additives are also added to clean the oil, reduce friction and reduce oxidation effects. Because they are human-made, synthetic molecules have a consistent mass and shape, helping them flow through the engine more smoothly.

Types of Synthetic Oil

There are two types of synthetic oil: fully synthetic and synthetic blend.

Fully synthetic oils are completely human-made without any petroleum, while a synthetic blend oil may have a high-quality conventional oil as a base. Because they require less time to produce, synthetic blends are often cheaper than fully synthetic oil, but fully synthetic oil offers better protection to your engine.

Pros and Cons of Synthetic Oil

Synthetic oil has been around since the 1930s, but it wasn't frequently used in cars until the 1980s. Proponents of synthetic oil claim the following benefits:

• Synthetic oil lasts longer. Synthetic oils are rated to last about twice as long as conventional oil, reducing your number of oil changes. While it varies based on brand, most synthetic oil manufacturers recommend you change synthetic oil between 10,000 and 15,000 miles or every six months or year.
• Synthetic oil keeps your engine cleaner for longer. Because synthetic oil is human-made, it contains fewer impurities than conventional oil. As a result, it resists the formation of deposits and sludge, improving your engine's performance.
• Synthetic oil is better for turbochargers. To create lighter, more fuel-efficient cars, manufacturers are building vehicles with smaller engines and a turbocharger.The turbocharger compresses air through the cylinder, allowing for faster speeds and better performance, but turbochargers require more oil flow in excessive heat conditions. Synthetic oil flows faster and degrades less under heat conditions than conventional oil, so manufacturers often recommend synthetic oils for vehicles with turbochargers.
• Synthetic oil has better viscosity. Synthetic oil is more stable than conventional oil so it has a better viscosity. This allows it to flow quickly and smoothly in all temperatures and resist extreme heat, improving your engine's performance.
• Synthetic oil may improve gas mileage and horsepower. Because synthetic oil flows so smoothly through the engine, it reduces friction. You may find your horsepower and gas mileage higher than if you used conventional oil.
• Synthetic oil performs better overall. Our Engine Oil Research study revealed that synthetic oil performs an average of 47 percent better compared to conventional oil in industry-standard tests. Most vehicles can use synthetic oil even though manufacturers recommend using conventional oil.

Despite its many advantages, synthetic oil has a few drawbacks that may keep you from choosing it for your next oil change:

• Synthetic oil is more expensive than conventional oil. Synthetic oil costs an average of twice as much as conventional oil. However, you'll require fewer oil changes over time, so the cost differential may even out over the vehicle's life.
• Synthetic oil may damage older engines. Synthetic oil is thinner than conventional oil, so it was initially thought to move through older engines too fast to adequately lubricate it or leak through small gaps in an older engine. However, new formulas are constantly being released that are designed for older engines, so consult your mechanic and owner's manual for their recommendations.
• The exact blend you want may not be available at your repair shop. Each synthetic oil blend varies based on the manufacturer. You may have to shop around to find an auto shop that offers the exact blend you're looking for since every auto shop won't stock every brand and blend.

Can You Use Synthetic Oil After Conventional?

You can switch between synthetic and conventional oil without harming your engine, but you should always drain the previous oil completely before adding the new oil type. While failing to do so won't harm your engine, it will prevent the oil from working to its fullest potential.

Keep in mind that using an oil your car's manufacturer doesn't recommend may void the vehicle's warranty, so consult your owner's manual and warranty paperwork before switching oil type.

7 Factors Influencing Which Type of Oil You Should Use

There isn't a one-size-fits-all answer to whether you should use synthetic or conventional oil in your vehicle. When deciding which oil to use in your car, consider the following factors.

Manufacturer Recommendations

The manufacturer's recommendation is the most important factor in determining which oil type to use. Your owner's manual will include the manufacturer's recommended oil type, oil specifications and oil change intervals. Violating these recommendations can damage your engine and even void your warranty.

Vehicle Age and Mileage

Many mechanics recommend using a high-mileage conventional oil for older engines with higher miles. These formulas often contain additives designed specifically for common problems in older engines, such as aging seals and increased oil consumption. Newer vehicles, especially those with a turbocharger, may require synthetic oil.

Operating Conditions

Conventional oil is often a good option for lighter driving conditions. However, if you frequently drive in extreme temperatures, tow heavy loads or engage in stop-and-go traffic, synthetic oil may better protect your engine from wear and tear.

Performance Requirements

High-performance vehicles such as sports cars are often harsher on engine oil than other models due to higher temperatures and other stressors. Synthetic oil provides better lubrication and lasts longer under these conditions, making it the better choice.

Budget Considerations

Price plays a significant role in determining which oil you use in your car. Synthetic oils cost more than conventional oils, but they last longer, so the cost may even out over the life of your car. Conventional oil is more cost-effective for most drivers, but you can opt for a synthetic blend to get some of the benefits of synthetic oil without paying as much as fully synthetic oil.

Oil Change Intervals

Synthetic oil may be a good option if you have a busy schedule or frequently forget when to get an oil change. It generally has a longer recommended change interval than conventional oil.

Whichever you choose, it's essential you follow the manufacturer's recommendation and your vehicle's maintenance reminder system for oil change intervals. Failing to do so can harm your engine and violate your vehicle's warranty.

Environmental Considerations

Synthetic oils are typically formulated to be more environmentally friendly than conventional oil. They do not create as much toxic waste since fewer oil changes are required, and they are specifically designed with lower toxicity and increased biodegradability. Synthetic oil may also slightly increase your vehicle's gas mileage and minimize emissions since it runs smoother. Some synthetic oils even have eco-friendly certifications or specifications.

Get Your Next Oil Change at a AAA-Approved Auto Repair Shop

Since oil changes are part of a regular maintenance routine for any car, AAA recommends you find an auto repair shop and technician you can trust.

AAA maintains a network of nearly 7,000 Approved Auto Repair facilities nationwide. These facilities meet AAA's high standards for appearance, technician training and certification, insurance coverage and customer satisfaction. As a AAA member, you'll receive special benefits , including auto repair discounts, extended warranties on parts and labor and AAA's support when resolving repair-related issues , at our approved facilities.