Engine oil is a crucial element for gasoline and diesel vehicles, as well as motorcycles. But what exactly is engine oil? What role does it play in a vehicle? What do the numbers and letters on engine oil packaging mean? And how do you choose the right oil for your car? Here’s everything you need to know about engine oil.

What Is Engine Oil?

Engine oil is primarily derived from crude oil and is known as base mineral oil. However, base mineral oil can degrade at high temperatures, which affects its performance and stability. To improve its properties, manufacturers often blend synthetic base oils (synthetic oils) and additives, resulting in semi-synthetic engine oil.

What Does Engine Oil Do?

Engine oil lubricates the various gears and shafts within the engine, reducing friction and lowering the high temperatures generated by rapid movement. It forms a protective film on gear surfaces, enhancing durability and efficiency.

Difference Between Semi-Synthetic and Full-Synthetic Engine Oil

Full-Synthetic Engine Oil

(Synthetic, Synthetic Based) contains no base mineral oil. It is made entirely from chemically synthesized oil and additives, offering excellent performance in high temperatures, lubrication, viscosity, and temperature adaptability. This type is widely used due to its superior properties.

Semi-Synthetic Engine Oil 

consists of a blend of base mineral oil and other synthetic oils and additives. It is often labeled as Semi-Synthetic. While it is less performant compared to full-synthetic oil, it is more affordable.

When Should You Change Your Engine Oil?

Engine oil should be replaced based on the vehicle’s mileage, usage frequency, and oil quality. Failing to change it regularly can reduce its lubricating ability and lead to the accumulation of metal particles in the engine.

Mileage: Different engines have different designs, so there is no universal number, but manufacturers usually specify in the owner’s manual how many kilometers to drive before changing the oil. Generally, oil should be changed every 5,000 to 10,000 kilometers. Even if you drive infrequently, it's recommended to change the oil at least once a year.

Usage Frequency: If the engine remains idle for long periods, oil can accumulate at the bottom of the engine, reducing its protective effectiveness. In such cases, choosing oil with lower viscosity can help it reach the working state more quickly.

Oil Quality: Higher quality oils provide better protection but do not extend the interval between changes indefinitely. Regular changes are still necessary depending on usage and mileage.

Understanding Engine Oil Labels and Numbers

Engine oil packaging features various letters and numbers, primarily following the SAE (Society of Automotive Engineers) standards. For example, SAE 0W-50 or SAE 10W-40. The letter “W” stands for Winter, indicating the oil’s viscosity in low temperatures; a lower number means lower viscosity and easier engine startup.

The numbers following “W” indicate the oil’s viscosity at high temperatures; higher numbers mean thicker oil, better for high-temperature performance.

Choosing the Right Engine Oil

The safest approach is to follow the recommendations in your vehicle’s owner’s manual, which suggests the appropriate oil viscosity. Depending on driving conditions and habits, slight adjustments can be made. For example, use oil with a lower "W" number in colder climates and higher viscosity oil, like 5W-50, in hotter regions like Hong Kong. Popular brands include Mobil 1, MOTUL, LIQUI MOLY, ENEOS, and Shell.

You can also assess oil quality through certifications:

API Certification 

The American Petroleum Institute’s standard, where the first letter (S or C) denotes gasoline or diesel use, and the subsequent letter represents testing standards. The closer to Z, the higher the standard, with P being the latest.

ACEA Certification 

The European Automobile Manufacturers' Association’s standard, using a letter and number to indicate oil type and quality, with higher numbers representing better quality.

Manufacturer Certification

Many car manufacturers, like Mercedes-Benz, BMW, Volkswagen, and Porsche, have their own certification standards that are stringent and specific to their vehicles.

How Long Does an Oil Change Take and What Does It Cost?

Engine oil changes are a standard maintenance task and can be completed in about 15 to 45 minutes. If you're not experienced with car maintenance, it's advisable to have a professional handle it to avoid issues such as leaks or engine damage.

Professional oil changes typically cost from a few hundred dollars, depending on the oil type and quantity required. Larger engines need more oil, and it’s also recommended to replace the oil filter to prevent contaminants from circulating in the engine.