I. Determining the Cause of Blackening
1. Normal Oxidation
It is normal for engine oil to oxidize and turn black under high temperature and pressure (especially for fully synthetic oil, which has a strong detergency and dissolves carbon deposits, which can easily turn black).
If the oil is black but has normal fluidity and is free of metal shavings, it can continue to be used until the end of the maintenance cycle.
2. Abnormal Contamination Signs
Rapid blackening in a short period of time (e.g., within a few days after an oil change) may be caused by residual old oil or poor fuel quality (high sulfur/olefins).
If the oil is milky white or contains metallic particles, immediately shut down the engine and inspect for internal wear or coolant leaks.
II. Targeted Treatment Measures
1. Routine Maintenance
Change the engine oil according to the maintenance interval (recommended ≤ 500 hours for fully synthetic oil, ≤ 250 hours for mineral oil).
Also, replace the oil filter to prevent impurities from circulating and contaminating the new oil. 2. Deep Cleaning
Use engine cleaning agent (add to old oil before changing and idle for 10-15 minutes) to dissolve sludge.
If severely contaminated, disassemble the oil pan and clean it, and check the crankcase ventilation system for blockage.
3. Fuel and Oil Optimization
Select low-sulfur fuel (sulfur content ≤ 0.05%) to reduce sludge formation.
Preferably use high-quality engine oil with an API CH-4 grade or higher.
3. Professional Testing Recommendations
Perform a filter paper diffusion test (a black spot with a diameter of less than 5mm in the center of an oil spot is considered normal).
Perform laboratory testing for acid value (>1.0mgKOH/g requires replacement) and flash point (<180°C is considered abnormal).
