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How to Read Engine Oil Grades? Decode the Performance Code of Engine Oil | AISO Lubricants Group
Release time:
2026-07-25
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Many car owners feel confused by the letter and number combinations on engine oil bottles, such as 0W-20, 5W-30, SP, and SN. What do these markings mean? What are the differences between various oil grades? Which one suits your vehicle best? In fact, engine oil grades serve as the exclusive "performance ID card" for lubricants, accurately indicating core parameters including low-temperature start-up performance, high-temperature protection capability, and overall quality level.
As a professional brand with in-depth expertise in the lubricant industry, AISO Lubricants Group focuses on the core demands of engine maintenance. Today, we will fully decode the complete meaning of engine oil specifications and teach you how to accurately read oil parameters and select the right lubricant for your vehicle. This helps you avoid common vehicle problems caused by incorrect oil selection, including increased fuel consumption, insufficient power, and engine wear.
I. Core Understanding: SAE Viscosity Grade – Temperature Adaptability of Engine Oil
Common oil grades such as 0W-20, 5W-30, and 5W-40 all comply with the SAE international lubricant viscosity standard, representing the core performance indicators of engine oil. Each grade is divided into two parts by a hyphen. The letter "W", derived from "Winter", stands for low-temperature adaptability. The numbers before and after W respectively indicate low-temperature fluidity and high-temperature protection performance.
1. Numbers Before W: Determine Low-Temperature Start-Up Performance – Smaller Values Mean Better Cold Resistance
The number before W represents the fluidity of engine oil in low-temperature environments, which directly affects engine protection during cold starts in winter. A smaller number means lower low-temperature viscosity and better fluidity. The oil can be quickly pumped to all engine components to form an effective oil film, minimizing dry friction and wear during cold starts, and adapting to lower ambient temperatures.
General industry temperature adaptation reference: 0W adapts to extreme low temperatures of -35°C; 5W adapts to -30°C; 10W adapts to -25°C; 15W adapts to -20°C. 10W and 15W lubricants are sufficient for regions with mild year-round climates in southern areas. For northern regions with severe winters, 0W and 5W low-viscosity oils are preferred to ensure smooth cold starts and protect core engine components.
2. Numbers After W: Determine High-Temperature Protection Performance – Larger Values Mean Stronger Protection
The number after W refers to the high-temperature viscosity and oil film stability of engine oil at the normal engine operating temperature (100°C). It is the core guarantee for engine operation under high temperatures, high speeds, and heavy loads. A larger number delivers higher high-temperature viscosity, thicker and more stable oil film, as well as excellent shear resistance, leakage prevention, and high-temperature resistance, effectively avoiding wear risks under high-load engine operation.
Adaptation scenarios for common grades are clearly defined: 20-viscosity oil is thinner with low resistance, low fuel consumption and excellent mute performance, suitable for new cars, small-displacement vehicles and hybrid models. 30-viscosity oil delivers balanced performance with both fuel efficiency and protection, serving as the all-season optimal choice for most family cars and SUVs. 40 and higher viscosity oils provide enhanced oil film protection, ideal for German cars, high-mileage vehicles, turbocharged models, and vehicles frequently operating at high speeds or under heavy loads.
II. Quality Classification: API Quality Grade – Quality and Technical Standards of Engine Oil
In addition to viscosity grades, markings such as SN, SP, and CK-4 on oil bottles represent the API (American Petroleum Institute) quality standard. These markings define the formula technology, cleaning performance, oxidation resistance and environmental protection level of engine oil, serving as key criteria for distinguishing oil quality. They are divided into two major systems: gasoline engine oil and diesel engine oil.
1. Gasoline Engine Oil (S Series)
Grades starting with the letter "S" are designed for gasoline engines. The later the suffix letter in the alphabet, the higher the oil quality level, the more advanced the formulation technology, and the more comprehensive the protective performance. The mainstream market grades in ascending order are SN and SP. As the current premium mainstream standard for gasoline engine oil, SP-grade oil features greatly improved resistance to low-speed pre-ignition (LSPI) and superior carbon deposit suppression compared with SN-grade oil. It effectively protects turbocharged and direct-injection engines, reduces engine vibration and power loss, and is fully compatible with China’s National VI and latest gasoline vehicle models.
2. Diesel Engine Oil (C Series)
Grades starting with the letter "C" are formulated for diesel engines, with common specifications including CK-4 and CI-4. They are primarily used for diesel-powered equipment such as trucks, pickup trucks and construction machinery. Higher-grade oils deliver better high-temperature stability, corrosion resistance and exhaust purification performance, compatible with the after-treatment systems of National VI diesel vehicles and effectively preventing DPF (Diesel Particulate Filter) blockage.
III. Practical Selection Guide: Avoid Mistakes in Oil Grade Selection for Different Scenarios
The ultimate goal of understanding oil grades is to select lubricants accurately. Based on years of market application experience, AISO Lubricants has summarized professional oil selection rules to help car owners avoid blind choices:
1. New vehicles (within 30,000 kilometers): Engine parts have precise clearances. Priority is given to 0W-20 and 5W-30 low-viscosity oils to reduce operating resistance, improve fuel economy, and ensure outstanding mute performance and power response.
2. High-mileage vehicles (over 80,000 kilometers): Slight component wear and enlarged clearances occur. It is recommended to upgrade to 5W-40 high-viscosity oil. The thickened oil film fills component gaps, reduces oil consumption and relieves engine abnormal noise.
3. Turbocharged & direct-injection models: Prioritize premium SP-grade lubricants with 5W-30/5W-40 viscosity, which effectively resolves common pain points including turbo overheating, low-speed pre-ignition and excessive carbon deposit build-up.
4. All-season optimal choice: Most regions across China feature moderate annual temperature variation. 5W-30 oil delivers a perfect balance of cold-start performance and high-temperature protection, making it the ideal all-round solution for most family vehicles. For extremely cold northern regions, 0W-series lubricants are highly recommended to avoid cold-start failure in winter.
IV. AISO Tips: Choose the Right Grade, and More Importantly, Premium-Quality Oil
Oil grades are the basic standard for lubricant selection, while the base oil quality, additive formula and production process directly determine the actual performance of the oil. With mature R&D and production systems, AISO Lubricants strictly complies with international SAE and API standards to manufacture full-spec compliant lubricants.
Our full-range products cover mainstream viscosity specifications including 0W-20, 5W-30 and 5W-40, as well as premium API grades such as SP and CK-4. Boasting outstanding low-temperature fluidity, exceptional high-temperature stability and powerful carbon cleaning performance, our lubricants deliver energy-saving and quiet operation for new vehicles, while providing durable heavy-duty protection for high-mileage vehicles and equipment under severe operating conditions. The complete product lineup suits passenger cars, commercial vehicles, construction machinery and all types of power equipment.
Selecting the correct oil grade is the first step of long-term engine maintenance. Master the performance code of engine oil and choose high-quality AISO lubricants to perfectly match your vehicle’s needs, reduce engine wear, extend service life, and keep every engine operating at peak performance for a long time.
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