What’s the Deal with Engine Oil Numbers?
If you’ve ever been in an auto parts store staring at rows of engine oil, you’ve probably seen labels like 5W-30, 10W-40, or 0W-20. But what do those numbers actually mean? And more importantly, does it really matter which one you use?
Short answer: Yes, and you should always follow the oil viscosity recommended by your vehicle’s manufacturer.
Those numbers tell you how your oil behaves under different temperatures and how well it protects your engine. Using an oil viscosity that doesn’t match your manufacturer’s recommendation can lead to poor lubrication, increased wear, and even engine failure over time. Let’s break it all down so you know exactly what’s going into your car and why it matters.
Understanding the Numbers: Viscosity Explained
The numbers on a bottle of engine oil represent its viscosity, or how thick or thin the oil is at different temperatures. The Society of Automotive Engineers (SAE) developed this system to help drivers understand oil performance in different conditions.
Take 5W-30 as an example.
- The first number (5W) – This refers to the oil’s viscosity in cold temperatures (W stands for “Winter”). A lower number means the oil flows more easily when it’s cold, making it easier for your engine to start in winter.
- The second number (30) – This indicates the oil’s viscosity at operating temperature (usually around 212°F). A higher number means thicker oil, which provides better protection at high temperatures.
So in simple terms, 5W-30 flows well in cold weather but still offers enough protection when your engine is hot.
Now, compare that to 10W-40:
- 10W – This means the oil is slightly thicker at cold temperatures than 5W oil, making it a little slower to flow in winter.
- 40 – This tells us the oil is thicker at high temperatures compared to a 30-weight oil, which could be beneficial in extreme heat or high-performance engines.
Why You Should Always Use the Oil Recommended by Your Manufacturer
While understanding oil viscosity is helpful, the most important rule when selecting an oil is to use the viscosity recommended by your vehicle’s manufacturer.
Manufacturers spend years testing engine oil to determine the ideal viscosity for performance, protection, and fuel efficiency. Using a viscosity that’s too thick or too thin for your engine can cause problems such as:
- Poor Cold-Start Protection: Oil that’s too thick in winter can make it harder for the engine to start.
- Excessive Wear and Tear: If the oil is too thin, it may not provide enough lubrication under high heat and stress.
- Reduced Fuel Economy: Using an oil that’s too thick can create extra friction inside the engine, reducing fuel efficiency.
Your owner’s manual will specify the correct engine oil for your car, often listing multiple viscosity options based on climate and driving conditions.
How Seasons Affect Engine Oil Performance
While manufacturers recommend specific oil viscosities, climate can influence oil behavior, especially in extreme conditions.
Cold Weather and Engine Oil
In cold temperatures, engine oil thickens, making it harder for your car to start. That’s why many modern vehicles recommend lower W-number oils, like 0W-20 or 5W-30, which flow better in winter conditions.
If you live in an area with harsh winters, check your owner’s manual to see if your manufacturer allows a lower viscosity for better cold-weather performance.
Hot Weather and Engine Oil
In hot climates, engine oil thins out, which can reduce its protective properties. Manufacturers sometimes specify a higher viscosity option for extreme heat to ensure proper engine protection.
However, modern synthetic oils are designed to perform well in both cold and hot weather, which is why many newer vehicles stick to one oil type year-round.
Conventional vs. Synthetic Oil: Does It Matter?
Yes. Synthetic oil is engineered to last longer, resist breakdown, and provide better protection than conventional oil. If your car requires synthetic oil, switching to conventional may reduce performance and increase sludge buildup.
Here’s a quick breakdown:
- Conventional Oil – Affordable, but breaks down faster and requires more frequent oil changes.
- Synthetic Blend – A mix of conventional and synthetic oil, offering better protection without the higher cost of full synthetic.
- Full Synthetic – Best for modern engines, high-performance vehicles, and extreme temperature conditions.
If your owner’s manual specifies synthetic oil, stick with it to keep your engine running at its best.
How Often Should You Change Your Oil?
Regular oil changes keep your engine running smoothly, but how often should you do them?
- Conventional Oil: Every 3,000-5,000 miles
- Synthetic Blend: Every 5,000-7,500 miles
- Full Synthetic: Every 7,500-10,000 miles
Your owner’s manual will provide the most accurate recommendation for your vehicle.
Can You Mix Different Oil Types or Viscosities?
In an emergency, yes—but it’s not recommended for regular use. Mixing oil viscosities (like 5W-30 and 10W-40) can alter oil flow characteristics and impact engine protection.
Stick with the oil type and viscosity recommended by your manufacturer for the best performance and longevity.
Get Your Next Oil Change at Madera Auto Repair
Not sure which engine oil is right for your car? Need an oil change but don’t want to deal with the mess? We’ve got you covered. At Madera Auto Repair, we provide expert oil change services using high-quality engine oil that matches your vehicle’s manufacturer recommendations.
📞 Call us at (559) 674-8207 or visit us at 2141 W Kennedy St, Madera, CA to schedule your next oil change today. Keeping your engine running smoothly starts with the right oil—let us help you make the best choice.
