What Type of Oil Should I Use in My Car?

If you've ever stood in the auto parts store staring at a wall of oil bottles, or handed your keys to a shop and wondered whether you got the right oil, you're not alone. Choosing the right motor oil genuinely matters, but it doesn't have to be confusing. This post breaks down the motor oil type selection guide most vehicle owners actually need: what the numbers mean, which type fits your car, and how to make the right call every time without guessing.

Start With Your Owner's Manual: It Has the Answer

Before anything else, check your vehicle's owner's manual. The manufacturer has already done the work for you. Inside, you'll find a specific oil viscosity grade recommended for your engine, something like 5W-30, 0W-20, or 5W-20, along with any performance certifications the oil should meet.

These recommendations aren't suggestions. They're based on the tolerances your engine was designed around. Using the wrong viscosity can affect how well your engine parts stay lubricated, especially during cold starts when most engine wear actually occurs.

If you no longer have your owner's manual, you can often find the recommendation:

• On a sticker inside your oil filler cap
• On a label inside your driver's side door jamb
• Through the manufacturer's website using your VIN
• By calling a local shop like Gregg Automotive: we're happy to look it up for you

The bottom line: your manufacturer's recommendation is the single most reliable starting point in any motor oil type selection guide. Everything else builds from there.

Understanding Viscosity: What Those Numbers Actually Mean

Motor oil labels display a viscosity grade that looks something like "5W-30." That notation tells you two things about how the oil behaves at different temperatures.

The number before the "W" (which stands for Winter) describes how the oil flows in cold temperatures. A lower number means the oil stays thinner and flows more easily when your engine is cold. The number after the dash describes the oil's thickness once your engine reaches normal operating temperature.

Here's a practical example:

• 0W-20: Flows very easily in cold weather; common in newer fuel-efficient engines, including many Honda, Toyota, and Subaru models
• 5W-30: A widely used grade that balances cold-weather performance with protection at operating temperature; found in millions of trucks and SUVs
• 10W-40: A thicker option sometimes recommended for older, higher-mileage engines

In the Kaufman County area, where summer temperatures regularly climb above 95°F and winters stay relatively mild, the cold-weather rating matters less than it would in northern states. That said, you should still follow your manufacturer's specification rather than adjusting on your own: modern engines are precisely calibrated.

According to the Society of Automotive Engineers (SAE), the organization that sets viscosity standards, even a one-grade difference from the manufacturer's recommendation can affect oil pressure and film strength inside the engine, particularly during the first few minutes after startup when approximately 75% of engine wear is estimated to occur.

Synthetic vs. Conventional vs. Synthetic Blend: Which One Is Right?

Once you know the right viscosity, the next question in any motor oil type selection guide is which base type to choose. There are three main options:

Conventional Motor Oil

Conventional oil is refined directly from crude oil. It's the most affordable option and works well in older, simpler engines that don't run under extreme temperatures or high stress. Most conventional oils are recommended to be changed every 3,000 to 5,000 miles, depending on your driving conditions.

Full Synthetic Motor Oil

Synthetic oil is engineered in a lab to have a more uniform molecular structure than conventional oil. That consistency means it flows more predictably at extreme temperatures, resists breakdown longer, and maintains protective properties across a wider range of conditions. Many manufacturers now require full synthetic oil, particularly in turbocharged engines, luxury vehicles, and most vehicles made after 2010. Full synthetic oil typically lasts 7,500 to 10,000 miles, and in some cases up to 15,000 miles, between changes, though your manufacturer's interval is still the final word.

Synthetic Blend Motor Oil

Synthetic blends combine conventional base oil with synthetic components to offer better performance than conventional oil at a lower cost than full synthetic. They're a popular middle-ground choice for truck owners, SUV drivers, and people who put moderate miles on their vehicles each year. Typical change intervals fall around 5,000 to 7,500 miles.

For most newer vehicles on the road today, full synthetic is the manufacturer-specified choice, not an upgrade, just the required product. If your vehicle is older or your manual specifies conventional oil, there's no need to switch.

Oil Certifications: API, ILSAC, and What They Mean for You

Beyond viscosity and oil type, look for the right quality certification on the bottle. These certifications tell you the oil has been tested and meets minimum performance standards.

The two most common you'll see in the U.S. are:

• API (American Petroleum Institute): Look for the API "donut" symbol on the label. The current top gasoline engine rating is SP, introduced in 2020. Previous ratings like SN and SM are still acceptable for older vehicles, but SP-rated oil meets the most current standards for engine protection and fuel economy.
• ILSAC (International Lubricant Standardization and Approval Committee): The starburst symbol on the label indicates ILSAC certification, which is required or recommended by many American and Japanese automakers. GF-6A and GF-6B are the current ILSAC standards as of 2021.

If your owner's manual lists a specific API or ILSAC rating, match it. If you're unsure, the team at Gregg Automotive can help you identify the right oil for your specific vehicle: no guesswork required.

High-Mileage Oil: Worth Considering After 75,000 Miles

If your vehicle has crossed the 75,000-mile mark, you may have noticed high-mileage oil on store shelves. These oils are specifically formulated for older engines and typically include seal conditioners to help aging gaskets stay flexible, along with added detergents and antioxidants to address the wear patterns that develop over time.

High-mileage oil is available in both synthetic and conventional formulations. It's not a requirement for every older vehicle, but for cars and trucks showing minor oil consumption or slight seepage, it can be a practical and affordable way to extend engine life without a major repair.

As you think about how oil type connects to how long you can go between services, it's worth reviewing oil change interval frequency to understand how mileage, driving habits, and oil type all work together.

Frequently Asked Questions

Can I switch from conventional oil to synthetic?

Yes, in most cases you can switch from conventional to synthetic oil without any issues. The old myth that synthetic oil causes leaks in engines previously run on conventional oil has been largely disproven with modern oil formulations. However, always confirm your engine's specified viscosity before switching, and if your vehicle is older or very high-mileage, discuss the change with a trusted mechanic first.

Does it matter which brand of oil I use?

Brand matters less than meeting the correct viscosity grade and certification standard. A store-brand oil that carries the correct API and ILSAC certifications will protect your engine just as well as a premium-branded oil of the same grade. What you want to avoid is using oil that doesn't meet the required certifications or viscosity: regardless of what's printed on the front of the label.

What happens if I use the wrong viscosity oil by mistake?

Using the wrong viscosity for a single oil change interval is unlikely to cause immediate damage in most cases, but it's worth correcting at your next service. An oil that's too thin may not maintain adequate pressure at operating temperature, while oil that's too thick may struggle to flow quickly during cold starts. If you're unsure what's currently in your engine, a shop can check it and advise whether an early change makes sense.

Is more expensive oil always better?

Not necessarily. The best oil for your car is the one your manufacturer specifies: full stop. A premium-priced synthetic that exceeds your engine's requirements isn't harmful, but it won't provide meaningful additional benefit over a correctly rated oil that meets spec. Spending more than necessary on oil doesn't translate to better engine protection if the viscosity and certification are already right.

The Right Oil Is Simpler Than It Looks

Choosing motor oil comes down to three things: the viscosity your manufacturer specifies, the oil type that matches your engine and driving needs, and a certification label that confirms quality standards are met. Once you understand those basics, this motor oil type selection guide gives you everything you need to make a confident decision, whether you're buying oil yourself or approving a service recommendation. When in doubt, the team at Gregg Automotive is always glad to help you sort it out, no pressure attached.