Is it okay to mix 5w30 and 5w40?
3 Answers
5w30 and 5w40 should not be mixed. Reasons why 5w30 and 5w40 cannot be mixed: Different grades of engine oil have varying performance characteristics. Additionally, engine technical requirements differ among manufacturers, leading to different viscosity requirements for the oil. Effects of mixing 5w30 and 5w40: It increases the engine's operating resistance, resulting in insufficient engine power. Prolonged mixing can affect the engine's lifespan and also increase fuel consumption. Correct oil selection method: A comprehensive analysis should be conducted based on the vehicle's driving environment, the owner's driving habits, and the vehicle's maintenance manual to select the appropriate oil viscosity for better engine protection.
I deal with car repairs quite often, and while mixing 5w30 and 5w40 oil isn't recommended, it's not catastrophic. The first number, 5w, indicates the same low-temperature viscosity for both, while the 30 and 40 represent differences in high-temperature viscosity. Mixing them can lead to unstable oil viscosity—potentially too thin at high temperatures, causing insufficient lubrication, or too thick, increasing fuel consumption. A small mix isn't a big issue, but prolonged or large-scale mixing can accelerate engine wear or cause cold-start difficulties. Engines are finely tuned for specific oils, and mixing disrupts this performance balance. In an emergency, a small top-up is acceptable as a temporary measure, but switching to a uniform type as soon as possible is best. Sticking to the manufacturer's recommended oil ensures longer-lasting protection—don't cut corners on maintenance to save a little money. Develop a habit of regular oil checks to avoid such mishaps.
As a car enthusiast, I was also curious about mixing engine oils, but the result was louder engine noise and slower power response. 5W30 is thinner at high temperatures, while 5W40 is thicker. Mixing them leads to imprecise viscosity, affecting lubrication. Protection decreases at high temperatures—short trips may be fine, but long-distance or aggressive driving increases wear risks. It's best not to mix; stick to one grade for stable performance. If accidentally mixed, top up with the same oil to dilute if the amount is small, or thoroughly flush the system at the next oil change. Always follow the manual’s specifications—good habits can double engine life and ensure worry-free driving.
