The importance of engine oil in car maintenance can never be overstated. Engine oil maintains the oil film and airtightness between the combustion chamber and the piston, and lubricates each part of the engine. It also performs numerous other functions - providing cooling, maintaining cleanliness, creating hydraulic pressure for various equipment, etc. Additionally, engine oil is oxidized and consumed in proportion to the engine running time, so the condition of the engine oil must be checked regularly. And when necessary, replenishing or changing engine oil is car maintenance 101.
Many people know that engine oil is important, but not many know for sure what type to put in it because there are so many different types. Then, you can easily choose the engine oil that is right for your car if you know these things - base oils, which are the basic components of engine oil, engine oil specifications related to performance, and viscosity.
Engine oil is made by adding additives to base oil. Base oil accounts for 80-90% of engine oil and has a significant impact on engine oil properties such as durability, viscosity index, evaporation amount, and solubility. Engine oil products on the market is made by adding additives to achieve the desired performance. Types of base oils are divided from group 1 to group 5. First, crude oil is distilled, impurities are removed with a solvent, and base oil is created through an atomic rearrangement process through hydrogen cracking. Base oils are classified into groups 1, 2, and 3.
Among them, Groups 1 and 2 are called mineral oils, and Group 3 is called synthetic oils. Although it is extracted from the same crude oil, the reason why only Group 3 is called synthetic oil is that it undergoes a hydrogenolysis process twice to raise the viscosity index to over 120. Although it is mineral oil, its chemical properties have changed significantly, so its performance is not much different from synthetic oil. The American Petroleum Institute (API) recognizes this as a synthetic oil, and if the viscosity index exceeds 130, it is classified as Group 3+.
Group 4 is made by synthesizing olefin using naphtha extracted from petroleum - commonly known as PAO, an abbreviation for Poly Alpha Olefin. Group 4 base oils have a high viscosity index, good low-temperature properties and are free of impurities. Group 5 refers to synthetic base oils excluding PAO. Esters, which are commonly used, are made by artificially synthesizing acids and alcohols. It has an excellent lubricating effect, but easily decomposes when reacted with moisture at high temperatures.
Engine oil has specifications, such as those set by the American Petroleum Institute and the European Automobile Manufacturers Association (ACEA). Engine oil specifications have continued to be revised as engine performance has improved. Therefore, engine oil made to the latest standards exceeds the performance required by engine oil of existing standards. So, it is okay to put the latest specifications of engine oil in an old car, but on the contrary, putting old specifications of engine oil in a new car is not a smart choice. As of 2023, the American Petroleum Institute uses ‘S’ (Service Station Classification) for gasoline engine oil, and is classified into SN, SN PLUS, SP, etc. in the order of creation.
The latest standard for gasoline engine oil is SP in 2020; This specification is designed to prevent low-speed pre-ignition and timing chain wear, as well as to protect against high-temperature deposits. The latest standards for diesel engine oil are CK-4 and FA-4 in 2017. FA-4 corresponds to low-sulfur fuel (up to 15ppm), and CK-4 corresponds to high-sulfur fuel (up to 500ppm).
The European Automobile Manufacturers Association sets the engine oil standard grade as ACEA-C and classifies it into gasoline engines, diesel engines, and diesel engines with exhaust gas after-treatment devices. Category A is for gasoline engines, Category B is for existing diesel engines, Category C is diesel engines equipped with after-treatment devices, and Category E is for large diesel engines installed in commercial vehicles. High-temperature and high-pressure viscosity affects exhaust gas after-treatment devices. The grades are different depending on the content of SAPS (sulfur dioxide, phosphorus, and sulfur).
SAPS is an additive intended to enhance anti-wear performance, but if burned in the engine, it can adversely affect aftertreatment devices, including the DPF. Therefore, it can be said that a feature of the European Automobile Manufacturers Association standards is that engine oils for diesel engines equipped with post-treatment devices are classified into grades by focusing on the mechanical characteristics of the engine, including reducing the SAPS content.
For those who like things simple, engine oil certified by automakers may also be a good option. These are the safest choice as they have passed tests conducted by auto manufacturers. However, products that do not have this certification are not necessarily bad; There are also engine oils made by adjusting the ratio of additives to suit each marketing strategy.
One of the important factors when choosing engine oil is the viscosity index. Viscosity index refers to the degree to which the viscosity of engine oil changes depending on temperature. If the viscosity change is small, the viscosity index increases. The viscosity grades of these engine oils are divided into low-temperature and high-temperature viscosity following the J300 classification of the Society of Automotive Engineers (SAE).
Here’s how to read engine oil viscosity: If we look at 5W-30 as a standard, W is from winter and means low temperature viscosity. The closer the first number is to 0, the lower the viscosity and the better the flowability at low temperatures. The 5W grade indicates a viscosity of 6,600 mPa.s or less at a temperature of –30℃, and the 0W grade indicates a viscosity of 6,200 mPa.s or less at a temperature of –35℃.
The number that follows refers to the high temperature viscosity. The higher the number, the higher the viscosity is maintained at high temperatures, forming an oil film suitable for lubrication. Grade 30 means a viscosity between 9.3 mm2/s and 12.5 mm2/s at a temperature of 100°C, and grade 40 requires a viscosity between 12.5 mm2 and 16.3 mm2. But higher numbers aren’t always better. The required engine oil viscosity varies depending on the characteristics of a car’s engine. If engine oil with a higher viscosity than necessary is used, engine internal resistance increases and power loss occurs. Conversely, if engine oil with a lower viscosity than required is used, an oil film may not be sufficiently formed at high temperatures and the engine interior may be worn.The number that follows refers to the high temperature viscosity. The higher the number, the higher the viscosity is maintained at high temperatures, forming an oil film suitable for lubrication. Grade 30 means a viscosity between 9.3 mm2/s and 12.5 mm2/s at a temperature of 100°C, and grade 40 requires a viscosity between 12.5 mm2 and 16.3 mm2. But higher numbers aren’t always better. The required engine oil viscosity varies depending on the characteristics of a car’s engine. If engine oil with a higher viscosity than necessary is used, engine internal resistance increases and power loss occurs. Conversely, if engine oil with a lower viscosity than required is used, an oil film may not be sufficiently formed at high temperatures and the engine interior may be worn.
Managing engine oil begins with reading the manual. The user manual contains various information such as the grade, viscosity, and replacement cycle of engine oil appropriate for each car. The recommended engine oil for Hyundai Santa Fe is 0W-30 that satisfies API SN PLUS/SP or ILSAC GF-6. In addition, in normal conditions, it is recommended to change the engine oil and oil filter every 10,000 km or 12 months, and in severe conditions, it is recommended to change the engine oil and oil filter every 5,000 km or 6 months. (* Based on Santa Fe MX5 2.5 Turbo 2023 model) In severe conditions, a short distance is recommended. Examples include repeated driving, excessive idling, and repeated driving in heavy traffic.
Engine oil is important, but more important than that is changing the engine oil regularly. If you use the engine oil for a long period of time beyond the replacement cycle, it may cause reduced lubrication performance, sludge generation, engine oil consumption, etc., and in the worst case, engine damage.
For those who want to keep their favorite car for a long time, read the manual to find out when to change the engine oil. And when it’s time to replace it, find the right engine oil. Choosing engine oil becomes easier if you know the conditions such as base oil, specifications, and viscosity. Now, have fun choosing engine oil.
HMG Journal Operation Teamgroup@hyundai.com
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