Can Castrol 30 and 40 engine oils be mixed?

[KaiRose]

Any base oils can be mixed, but engine oils are not recommended for mixing due to different additives that may cause chemical reactions and degrade oil performance. However, oils from the same brand have roughly the same additive formula, so Castrol 30 and 40 engine oils can be mixed. Engine oil specifications: Engine oil specifications include two parts: classification and viscosity grade. Oil classification is represented by a combination of two letters, such as SA. Oil viscosity is usually indicated by SAE grades, such as 5W-40. 'S' stands for gasoline engine oils, with general specifications ranging from SA to SN (in alphabetical order, excluding SI). Each subsequent letter indicates better oil performance than the previous one. The numbers following the oil classification represent its viscosity grade. 'W' stands for winter, and the smaller the number before it, the better the oil's low-temperature fluidity, indicating it can be used in lower environmental temperatures and provides better engine protection during cold starts. The number after 'W' indicates the oil's high-temperature resistance, with higher numbers representing better protection at high temperatures. Castrol: Castrol is a globally recognized lubricant expert and a subsidiary brand of BP (British Petroleum).