Is it okay to add a little gear oil to engine oil?
2 Answers
Under normal circumstances, adding a small amount of gear oil to the engine by mistake will not cause major issues. Here are the specific details: Introduction: Since the engine itself requires engine oil, adding a small amount of gear oil will dissolve and dilute it. Gear oil and engine oil share similarities in their operating principles for the engine. Gear oil also has a lubricating effect, but its viscosity is too high, and the oil film is too thick, which may prevent the oil from reaching the precisely fitted components, thereby accelerating engine wear. If you are concerned about potential problems, you can directly drain it and replace it with new engine oil and an oil filter. Due to the differences in usage conditions, composition, and performance between internal combustion engine oil and gear oil, they should not be mixed. Differences: The performance and functions of gear oil and engine oil are entirely different, so they should not be mixed. If the vehicle shows no abnormal noises, immediately drain the engine oil and replace the oil filter. Clean the system with flushing oil. If flushing oil is not available, add engine oil, start the car, let it idle to warm up, then drain the oil again, refill with fresh engine oil, and replace the oil filter again.
As someone who frequently works on cars themselves, I strongly advise against doing this. Gear oil has extremely high viscosity and contains a bunch of sulfur-phosphorus additives specifically designed to handle the high-pressure friction of gears. But when you mix it into engine oil, the entire formulation gets messed up. I remember a friend who tried to save money by mixing some in, and after just 500 kilometers, the engine started sounding muffled. When we opened it up, we found the piston rings were scored. Engine oil and gear oil are like mixing soda and soy sauce – it might seem fine in the short term, but under high temperature and pressure, they can form gel-like deposits, essentially like sprinkling sand into the oil passages. Not only does this clog the filter, but it also causes metal friction surfaces to grind directly against each other. Now, replacing a camshaft assembly costs two to three thousand, so it's better to just buy a bottle of qualified engine oil.
