What are the consequences of mixing 5w40 and 5w30 oils of the same brand?

[MacKeira]

The consequences may include inadequate engine protection, affecting driving performance, increasing engine operating resistance, causing insufficient engine power, and even impacting the engine's service life. Additional information: To protect the engine: It is recommended not to mix oils of different brands or specifications. When switching to another brand or type of oil, remember to drain the existing oil completely to allow the new oil to perform its functions better, thereby protecting the engine more effectively and extending its service life. Engine oils: Currently, there are three types of engine oils available on the market: mineral oil, semi-synthetic oil, and fully synthetic oil. However, fully synthetic oil is the most commonly used due to its superior quality and performance compared to mineral and semi-synthetic oils.