Is 10W-40 Oil Fully Synthetic?
2 Answers
10W-40 oil is not fully synthetic; it is a Group II mineral oil. Generally, 10W-40 oil is a semi-synthetic oil, which is a blend of fully synthetic oil and mineral oil in a certain ratio. This type of oil has a relatively lower lubrication grade compared to fully synthetic oil, and its replacement cycle is correspondingly shorter. Typically, it should be replaced every 5,000 kilometers or every six months. 10W-40 oil is commonly used in tropical regions, areas with hot summers, or in older vehicles with higher mileage. The method for changing the oil is as follows: Wait for the engine temperature to cool down, allowing the oil to flow back into the oil pan; Use a wrench to loosen the oil drain plug and place an oil pan underneath to catch the old oil until it stops flowing. Start the engine for 30 seconds to allow the oil in the main oil passage to drain out; Use a specialized wrench to remove the oil filter; Apply oil to the oil seal of the new oil filter and tighten it clockwise by hand; Add the new oil through the engine valve cover's oil filler port, typically filling up to three-quarters of the oil container; Start the engine and let it run for 5 minutes, checking for any oil leaks around the oil drain plug and oil filter. If leaks are found, perform necessary repairs; After stopping the engine, pull out the oil dipstick to ensure the engine oil level is within the standard range.
I've been repairing car engines for over twenty years and have encountered this issue countless times. The numbers 10w-40 represent the viscosity grade of the engine oil, which isn't directly related to being fully synthetic. Viscosity refers to the thickness of the oil—10w indicates better flow at low temperatures in winter, while 40 means stronger protection at high temperatures in summer. Fully synthetic refers to the base oil being made from artificially synthesized materials, offering greater durability and environmental friendliness. However, among oils labeled 10w-40, there can be fully synthetic, semi-synthetic, or mineral oils, depending on the brand and product line. For example, some premium oils clearly state 'Fully Synthetic' on the bottle, while cheaper products might blend in mineral oil. In daily driving, synthetic oils can extend oil change intervals to over 10,000 kilometers, making them more suitable for high-performance engines. I recommend carefully reading the label before purchasing oil—don't just look at the viscosity grade. This small detail can prevent major engine damage.
