How to Determine When Engine Oil Needs Replacement
4 Answers
Methods to determine when engine oil needs replacement are: 1. Smell Test: Pull out the dipstick and smell it closely. If there is a strong sour odor, it indicates the oil has deteriorated and needs replacement. 2. Finger Rub Test: Rub the extracted old oil repeatedly between your thumb and index finger. If you feel impurities, poor viscosity, or even grittiness, replacement is needed. 3. Color Identification Test: Place a few drops of old oil on a clean white filter paper. After the oil seeps through, if it appears dark brownish-black with impurities, replacement is required. 4. Light Inspection Test: Hold the dipstick at a 45-degree angle under light to observe the oil droplets. If there are excessive metal particles, replacement is necessary.
As a veteran taxi driver with 20 years of experience, let me tell you that checking engine oil is all about observation. Pull out the dipstick - fresh oil is translucent amber, while used oil turns black like cola. Dip your finger in and rub it; if it feels gritty or has metal particles, change it immediately. If the oil film on the dipstick is too thin to cling properly, that's another sign it needs changing. I make it a habit to check every 3,000 kilometers, changing more frequently with heavy city traffic. Last time I saw a young guy drive until his oil turned black and solidified - ended up costing him over 8,000 yuan for an engine overhaul, what a painful lesson!
Last month, right after my car's maintenance, the mechanic taught me a simple trick: take a white tissue paper and drip some engine oil from the warmed-up car. Fresh oil forms three distinct diffusion rings, with the outermost being light yellow. My car had been running for eight months, and the oil dripped only formed a murky dark stain with black spots in the center. The mechanic said this indicates reduced lubricity and that the detergents in the oil have degraded, which could lead to a significant increase in fuel consumption if driven further. Now, every time I wash my car, I test the oil this way—it's much more accurate than checking the odometer.
As an engineering-minded person, I trust test data more. The 20-yuan oil test paper bought on Taobao works great – just drip the oil and let it sit for eight hours, then observe the color stratification of the oil ring. If the light-yellow ring exceeds 4mm, you can keep driving. Last time, my car's ring width was only 1.5mm (corresponding to the aging threshold). Last week, I used a viscosity tester and found the new oil's 100°C viscosity was 14.2, but it has now dropped to 11.8, far below the manufacturer's required minimum of 12.5. These hard metrics are more reliable than gut feelings. I recommend combining them with the oil change intervals in the maintenance manual for a comprehensive judgment.
