The short answer is that it is generally not recommended to mix different types of motor oil, including high mileage synthetic oil and regular synthetic oil. Doing so can potentially compromise the performance and effectiveness of the oil, leading to engine problems and reduced longevity.
High mileage synthetic oils are specifically designed for use in engines with high mileage and have additional additives that help to reduce oil consumption, engine wear, and seal leaks. Regular synthetic oils, on the other hand, are formulated to provide superior engine protection and performance.
Mixing these two types of oil can result in a number of problems. First, the additives in the high mileage oil may not be compatible with the regular synthetic oil, which can lead to a reduction in the effectiveness of the additives. This can ultimately result in increased engine wear and tear, as well as reduced fuel economy.
Additionally, mixing different types of oil can result in unpredictable and inconsistent performance, as the viscosity and other properties of the oil can be altered by the mixing process. This can lead to issues such as engine sludge buildup, decreased oil flow, and reduced engine efficiency.
In some cases, mixing different types of oil may be acceptable, such as if a small amount of one type of oil is added to a nearly-empty oil reservoir that already contains the other type. However, even in these situations, it is generally best to avoid mixing different types of oil whenever possible.
Ultimately, it is important to follow the manufacturer’s recommendations when it comes to choosing and using motor oil. Using the right type of oil for your engine and following the recommended oil change intervals can help to ensure optimal engine performance and longevity. If you are unsure about which type of oil to use, consult your vehicle owner’s manual or speak to a qualified mechanic.