I. Basic Identification Methods
1. Color Observation
New engine oil is usually light yellow or golden yellow. It is normal for it to gradually turn brown after use.
If the oil is dark black and turbid (similar to ink), or milky white (possibly due to coolant contamination), it indicates serious deterioration.
2. Filter Paper Diffusion Test
Drop engine oil onto qualitative filter paper and let it sit for 1 hour before observing the oil spot:
Normal oil spot: uniform color, distinct diffusion ring, and shallow sedimentation ring.
Abnormal oil spot: dark black and dense sedimentation ring, narrow or absent diffusion ring.
II. Auxiliary Detection Methods
1. Texture and Odor Check
Dip your finger into the engine oil and rub it. It should be smooth and free of grains. If it feels rough or has metal shavings, it indicates serious contamination.
Normal engine oil has only a faint odor. If it has a sour or burnt odor, it indicates deterioration. 2. Oil Fluidity Test
Observe the fluidity of the oil as it pours. If it's thick like syrup, replace it immediately.
3. Professional Testing Recommendations
Laboratory Testing: Use indicators such as acid value (>1.0mgKOH/g requires replacement) and flash point (<180°C indicates abnormality).
Magnetic Oil Drain Plug: Absorbs metal particles and helps determine internal wear.
