What Do the Numbers on Oil Mean?
We all know that engine oil is important and has a big impact on how our cars run, but what do the numbers on oil actually mean and how does it function? Keep reading to learn about oil viscosity and the best oil for your car.
Our cars have many moving parts which cause friction and generate heat. Engine oil absorbs that heat and lubricates the engine, ensuring it runs smoothly. Each oil will list its grade using letters and numbers to indicate viscosity. The oil viscosity refers to the thickness of the oil and how it will move through engine components. The viscosity of the oil matters because it determines how well the oil flows in different temperatures, determining performance in different conditions. Understanding these numbers is crucial for car maintenance.
Understanding Oil Viscosity Ratings
Oil viscosity is the thickness of the oil and it is essential for engine performance in a number of ways:
Lubrication: Reducing friction between moving parts of the engine, thus preventing wear and tear and allowing the engine to function smoothly.
Cooling: Absorbing heat and cooling the engine down by moving the heat away from critical parts.
Cleaning: Maintaining a clean engine by trapping dirt and preventing damage.
Sealing: Preventing gases from escaping the combustion chamber.
Corrosion Protection: Forming a layer of protection on engine parts to protect from rust and corrosion.
Pressure Regulation: Maintaining consistent pressure throughout the lubrication system.
Oil viscosity is the ratio of pressure to flow rate. In short, it is the resistance to flow. Car oils have different viscosity ratings which are standardized by the Society of Automotive Engineers (SAE). The SAE developed a global standardized system for classifying engine oil viscosity. It works with manufacturers and industry experts to test oils. This global testing system has allowed for universal viscosity ratings, contributing to a streamlined market for car oils. The SAE’s standardized viscosity system also means that oils are labeled consistently, regardless of brand, making it easier to compare oils with the same rating.
What Do the Numbers on Oil Mean?
Most oils used today are multi-grade oils. These oils work well year-round, despite the season or temperature. The grade of oil will usually be “number + W + number” for example “5W-30.”
The “W” means “winter.” The number before the “W” represents the cold winter viscosity grade and the engine’s ability to start at low temperatures. The lower the number, the easier it is for the engine to run.
Whereas the number after the “W” indicates the oil viscosity grade in high temperatures. A high number indicates optimal component protection and engine sealing. This is because a thick layer of oil forms in the engine’s hotter areas. However, a lower number is more effective in improving fuel consumption and reducing friction between hot parts.
How Cold Weather Affects Oil
Oil becomes thicker and more viscous when temperatures drop, so its important to choose the right W-rated oil in winter. If the oil is too thick, it is more difficult to flow through the engine. A lower “W” number (e.g. 5W) means that the oil will flow more easily when it is cold outside. This will not only ensure a smoother start but also reduce strain on the engine. Here are a few more reasons why a lower W number is essential in the winter:
Minimized engine wear: Engine parts are not fully lubricated when you start your car in cold weather. Oil takes longer to circulate, resulting in parts being unprotected for longer. A lower oil viscosity will help reduce friction.
Faster lubrication: Oil flows more slowly in cold weather. Lower W-number oils reach critical engine parts more quickly to minimize any potential damage.
Better fuel efficiency: If the oil is too thick, it causes more drag on the engine, making it work harder and consume more fuel. As a result of helping the engine operate more efficiently, lower W-rating oils also help save fuel in cold weather.
Prevention of oil breakdown: Oils designed for warmer weather can fail to circulate in very low temperatures. This will not protect your engine, so a lower W-grad oil is best to ensure an effective engine during winter.
To help break down the best oil for winter driving, here is a comparison between 0W, 5W and 10W oils:
0W: This oil is best for extremely cold temperatures. It flows the easiest in very cold weather, even below freezing. It reduces engine damage by getting to critical parts quickly and provides the fastest lubrication during cold starts.
5W: This oil still works well for cold starts, but it does not flow as quickly as 0W. It is great in climates with low temperatures but not as severe as those requiring 0W grade oil.
10W: This oil is thicker and slower to flow to the engine in cold weather than 0W and 5W. It is good for mild winters where it doesn’t get too cold.
How Hot Weather Affects Oil
High temperatures affect an oil’s viscosity and ability to protect the engine. The second number in the oil rating (the number after the “W”), is important for warm climates as it indicates how an oil might protect the car in hot weather.
Oils with a higher second number (e.g. 10W-50) are designed to stay thicker in higher temperatures. In increased heat, oil becomes thinner. This can be a problem as it may not be able to form a thick enough barrier to protect between engine parts. A thicker grade oil helps maintain proper lubrication even when the engine gets hot.
Here are some other reasons why a higher grade second number oil is the best oil for hot weather:
Engine heat: The engine itself gets hotter in hot weather. As it heats, the oil needs to keep a higher viscosity to provide effective lubrication.
Overheating risk: If an oil is too thin for hot weather, it is unlikely to properly cool the engine. This can lead to overheating or even damage.
Oil loss: Hot weather can result in the evaporation of lighter oil components. This can result in the oil level dropping and reducing the lubrication available for the car’s engine.
Oil degradation: Oil undergoes a chemical reaction called oxidation when exposed to extreme heat. This forms sludge and varnish that can clog oil passages and reduce its effectiveness.
Here are some examples of common warm-weather oil choices:
5W-30: This is a commonly used multi-viscosity oil that works well in many climates, including warmer temperatures. The “30” indicates that it can handle high operating temperatures and it is a middle-range viscosity oil.
10W-40: This oil is thick and performs well in both high and cold temperatures. It is good for older engines or high-performing cars that have high wear rates.
15W-40: This oil is often used in diesel engines. It provides strong protection in high heat and is often used in commercial vehicles and heavy-duty trucks.
20W-50: This thicker oil is often used in vehicles with higher mileage and more wear like performance or classic cars. It is designed for extreme heat conditions and can help prevent leaks.
Choosing the Right Oil for Your Vehicle
There are multiple factors to consider when determining the best oil for your car. Here are a few things to keep in mind:
Manufacturer recommendations: Your car’s owner manual will provide information regarding the specification for both the type of oil and the oil viscosity your car requires.
Climate: Your climate will play a role in choosing the optimum oil. A lower W-rating (e.g. 0W) will be beneficial in freezing climates, whereas a higher second number (e.g. 10-40) will be better in hotter ones. In varied climates, a multi-viscosity oil (e.g. 5W-30) will balance out across hot and cold temperatures.
Driving habits: How you drive affects the oil in your engine. For example, if you only take short trips or are often in stop-and-go traffic, the engine might not fully warm up, so a synthetic or high-viscosity oil may help against wear.
Engine age: Older engines often benefit from high-viscosity oils that help fill gaps that form over time. Newer engines however are designed to work well with synthetic oils, which maintain performance and fuel economy.
When choosing the oil for your car, it is important to understand the difference between synthetic and conventional oils. Synthetic oils have been designed to perform in extreme weather and last for long periods. They are often preferred in cold weather, heavy-duty driving conditions and for long oil change intervals.
Meanwhile, conventional oils are less expensive and derive from crude oil. They are better suited for drivers in milder climates and with less demanding driving habits.
An oil’s viscosity can also impact fuel efficiency and engine longevity. Choosing the right viscosity is a balance of protection and efficiency. Lower-viscosity oils reduce friction and increase fuel efficiency, but they may not offer enough protection in extreme conditions. Meanwhile, higher viscosity oils provide better protection for heavy-duty driving and older engines but have the potential to reduce fuel efficiency due to increased resistance.
Common Myths About Engine Oil Numbers
There are many myths about engine oil numbers, so let’s debunk them for you:
“Thicker oil is always better”: While thick oil is ideal for high-mileage engines, high temperatures and heavy-duty driving, it can also reduce fuel efficiency and provide inadequate lubrication in cold weather. Optimal oil viscosity depends on the climate, engine and driving conditions.
“You can use any oil as long as it’s fresh”: While fresh oil may be attractive, it may not be best for your vehicle. A compatible oil should have the correct viscosity and be the right type for your car.
“Synthetic oil is only for high-performance cars”: Synthetic oil is versatile and can benefit many types of cars. While it provides better performance in extreme conditions, it can also offer improved protection and extended intervals between oil changes for standard passenger cars.
FAQs About Oil Viscosity
Still have questions about oil viscosity? This quick FAQ should help you determine the best oil viscosity for your vehicle:
Can I mix different oil viscosities?: This is not recommended as it can lead to inconsistent lubrication and poor engine performance. In an emergency, you can mix different oils of the same type (both synthetic). You should replace this with the correct oil as soon as possible.
What happens if I use the wrong oil viscosity? This can lead to poor performance, reduced fuel efficiency, overheating, engine wear and even damage. If you use the wrong oil by accident, you should replace it with the correct viscosity as soon as possible to avoid damage.
Do high-mileage cars need different oil? Specialized oils have been formulated for cars with high mileage (over 75,000 miles). These synthetic oils contain seal enhancers and additives that will minimize oil leaks. These oils are recommended, especially if your car is experiencing increased oil consumption or rough performance.
Oil viscosity impacts performance, temperature resistance and engine health. Choosing the best oil for your car is paramount to ensuring its maintenance and performance. It is recommended to check your owner’s manual for manufacturer recommendations for the best oil for your vehicle. It is also important to make regular oil changes for engine longevity.
