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AISO Lubricants Guide: Differences Between CI-4, CJ-4 and CK-4 Diesel Engine Oil Grades & Selection Rules for China V/VI Emission Vehicles
Release time:
2026-07-31
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With the continuous upgrading of commercial vehicle emission standards, China V and China VI emission vehicles have been fully popularized. The selection of diesel engine oil is no longer a simple viscosity matching process. The accurate differentiation of three mainstream API diesel oil grades (CI-4, CJ-4 and CK-4) directly determines engine service life, after-treatment system stability and vehicle annual inspection pass rate. As a professional brand deeply engaged in the lubrication industry, AISO Lubricants, relying on stringent oil R&D standards, thoroughly analyzes the core differences between the three diesel engine oil grades for vehicle owners, logistics fleets and maintenance practitioners. It also provides exclusive selection schemes for China V and China VI emission vehicles, helping users adopt scientific oil selection practices, avoid maintenance risks and reduce vehicle operating costs.
I. Core Logic of API Diesel Engine Oil Grades: Higher Alphabetical Order Represents Superior Grade and Performance
API diesel engine oil quality standards are classified by alphabetical order for the C-series oils. The later the alphabetical letter, the more advanced the oil R&D technology, the stricter the performance indicators, and the higher the emission standard of compatible vehicles. CI-4, CJ-4 and CK-4 are the mainstream mid-to-high-end diesel engine oil grades in the current market, featuring gradual upgrading, upward compatibility and no downward substitution. In short, higher-grade engine oil can be used for vehicles with lower emission standards, while lower-grade engine oil is strictly prohibited for high-standard China VI emission vehicles.
II. Detailed Differences Between CI-4, CJ-4 and CK-4 Diesel Engine Oil Grades
1. API CI-4: Classic Cost-Effective General Grade for Old and Medium Emission Vehicles
As a classic diesel engine oil grade suitable for China III, China IV and early China V emission vehicles, CI-4 is a widely popularized basic high-performance oil in the market, featuring stable durability and outstanding cost performance. Developed for early electronically controlled turbocharged and high-pressure common rail diesel engines, this grade of oil delivers excellent high-temperature oxidation resistance, wear resistance and sludge inhibition capabilities, effectively adapting to the operating conditions of old engines and scenarios with high-sulfur fuel.
In terms of core characteristics, CI-4 oil has a relatively high ash content, and its additive system focuses on basic lubrication protection without special optimization for exhaust after-treatment systems, making it incompatible with China VI vehicles equipped with DPF (Diesel Particulate Filter). It boasts wide adaptability, high fault tolerance and good compatibility with high-sulfur fuel, with a stable oil change cycle. It is ideal for old engineering vehicles, agricultural vehicles, light trucks compliant with China IV and lower emission standards, as well as early China V vehicles without sophisticated after-treatment devices.
2. API CJ-4: Transitional Advanced Grade Balancing Protection and Emission Adaptability
CJ-4 is an advanced transitional grade between CI-4 and CK-4, specially developed for mid-to-late China V and entry-level upgraded China V emission vehicles, with core optimizations focused on exhaust emission adaptability. Compared with CI-4, CJ-4 features greatly reduced sulfur, phosphorus and ash content, minimizing oil combustion residues and exhaust pollutant emissions. It provides basic adaptability to standard after-treatment devices and reduces the risk of carbon deposit blockage.
In terms of performance, CJ-4 has upgraded high-temperature attenuation resistance and corrosion resistance, capable of withstanding heavy-load and long-distance high-intensity operating conditions, with better engine quietness and power stability than CI-4. While maintaining compatibility with high-sulfur fuel, it meets the emission requirements of China V vehicles and is backward compatible with China III and China IV vehicles, serving as a cost-effective preferred choice for mid-end fleets. However, it has obvious shortcomings in long-term durability, low ash control and DPF protection compared with the top-tier CK-4 grade.
3. API CK-4: Top Flagship Grade, Exclusive Standard for China VI Emission Vehicles
As the highest-specification API-certified diesel engine oil grade at present, CK-4 is exclusively developed for stringent China VI emission standards and serves as the flagship oil for modern high-end commercial vehicles. It adopts an ultra-low sulfur, ultra-low phosphorus and ultra-low ash formula system, fundamentally reducing combustion carbon deposits and particulate residues. It perfectly matches the DPF and SCR (Selective Catalytic Reduction) systems standard on China VI vehicles, completely solving core problems such as after-treatment device blockage, failure and annual inspection non-compliance.
CK-4 achieves all-round upgrades in comprehensive performance: greatly enhanced oxidation and aging resistance for extended long-term oil change cycles; stronger wear resistance and emulsification resistance to adapt to extreme operating conditions including long-distance heavy load, high-speed high temperature and complex mountain road conditions; superior oil cleaning and dispersion performance that continuously inhibits engine sludge and carbon deposit formation to maintain stable long-term engine operation. Meanwhile, CK-4 is fully compatible with all China V, China IV and China III diesel vehicles, making it an all-round diesel engine oil with the best universality and protection performance.
III. Precise Oil Selection Guidelines for China V & China VI Diesel Vehicles
1. China V Diesel Vehicles: Flexible and Customizable Selection Based on Demand
China V vehicles adopt a relatively simple after-treatment system without strict DPF blockage restrictions, enabling flexible oil selection based on vehicle condition, operating conditions and budget.
Budget-Economic Option: For aging China V light trucks, engineering vehicles and short-distance transport vehicles, AISO CI-4 diesel oil is the optimal choice. It provides in-place basic lubrication protection, adapts to conventional operating conditions with high cost performance, and meets daily operation and annual inspection requirements.
Balanced Practical Option: For mid-end China V heavy trucks, long-distance logistics vehicles and high-frequency operating vehicles, AISO CJ-4 diesel oil is recommended. It balances power protection and emission adaptability with stronger attenuation resistance, effectively extending the service life of engines and basic after-treatment devices.
Long-Term Protection Option: For China V fleets pursuing long-term maintenance and high-intensity heavy-load operation, AISO CK-4 diesel oil can be directly upgraded. Its top-tier oil performance further reduces engine wear and carbon deposit formation, extends oil change cycles and lowers overall maintenance costs.
2. China VI Diesel Vehicles: Mandatory High-Grade Oil, No Downgraded Oil Allowed
China VI vehicles are equipped with sophisticated DPF and high-efficiency SCR after-treatment systems that impose extremely strict requirements on oil ash, sulfur and phosphorus content. The use of low-grade CI-4 and CJ-4 oil is strictly prohibited. Low-grade oil produces a large amount of ash particles after combustion, which will rapidly block the DPF, resulting in reduced vehicle power, increased fuel consumption, illuminated malfunction indicators, and even permanent damage to after-treatment devices with maintenance costs up to thousands of yuan.
All China VI diesel heavy trucks, light trucks, passenger buses and special operation vehicles shall be uniformly equipped with AISO CK-4 ultra-low ash diesel oil. Adopting a high-end environmentally friendly formula, AISO CK-4 oil accurately matches the working logic of China VI after-treatment systems. It provides comprehensive protection for core engine components against wear caused by heavy load, high temperature and frequent start-stop operation, and effectively avoids DPF blockage and frequent regeneration problems. It ensures stable emission compliance and long-term efficient operation of vehicles, fully meeting the stringent emission and operating requirements of China VI standards.
IV. AISO Lubricants Selection Summary & Maintenance Tips
For quick and convenient oil selection, the core rules are summarized as follows: CI-4 is suitable for China III, China IV and early China V vehicles with high cost performance; CJ-4 applies to all China V vehicles with balanced performance and economy; CK-4 is universally compatible with all emission-standard vehicles and serves as the exclusive high-performance long-term maintenance option for China VI vehicles.
It is reminded that diesel engine oil follows the strict principle of upward compatibility and no downward compatibility. China VI vehicle owners shall never use low-grade oil for cost-saving purposes. For operating conditions with high-sulfur fuel, blind use of CK-4 is not recommended; CJ-4 or CI-4 can be selected according to vehicle condition for better adaptability.
Adhering to stringent oil R&D and quality control standards, AISO Lubricants builds a full-coverage diesel oil product matrix adaptable to all operating conditions and emission standards. From basic protection to high-end long-term maintenance, we provide professional and reliable lubrication solutions for all types of commercial vehicles, empowering efficient operation and prolonged service life of every vehicle.
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