Here are a few reasons why mixing 10w40 and 15w40 engine oils may not be ideal:
1. Viscosity Differences: 10w40 and 15w40 oils have different viscosities. The "w" in the oil grade stands for "winter," and the numerical value before the "w" indicates the oil's viscosity at low temperatures. The higher the number, the thicker the oil is at low temperatures. Mixing these two oils may result in an inconsistent viscosity blend that may not provide optimal engine protection across various temperature ranges.
2. Additive Incompatibility: Engine oils contain various additives that serve specific purposes, such as detergency, dispersancy, anti-wear protection, and corrosion resistance. Different oils may have different additive packages, and mixing them might lead to additive interactions or imbalances, possibly reducing the overall effectiveness of the oil.
3. Potential Sludge Formation: Mixing oils with different additive chemistries can sometimes lead to the formation of sludge or deposits within the engine. Sludge can clog oil passages, restrict oil flow, and cause premature wear on engine components.
4. Warranty Concerns: Mixing different oils might void the vehicle's warranty if it goes against the recommendations provided by the manufacturer. Always refer to the owner's manual or consult with an authorized dealership to ensure you are using the correct oil type and viscosity for your vehicle.
If you accidentally mixed these two oils, it's generally advisable to have the oil drained and replaced with the correct oil recommended by the vehicle manufacturer as soon as possible. Consult with a qualified mechanic or refer to your vehicle's owner's manual for guidance on oil selection and maintenance.
