Mixing engine oils

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The different types of engine oils are mineral/regular oil, semi-synthetic oil and pure synthetic oil. Each has its advantages and disadvantages, and performs differently under varied conditions. Is mixing synthetic and regular oil to get better performance at a lower price a good idea?

The good news is that it will not harm your engine in any way in the short term. Most synthetic and semi-synthetic engine oils are based on regular oil and are compatible. No unwanted by-products are created when different types of oil are mixed, and engine performance will be fine.

The bad news is that this will not give you the benefits you think it would. Mixing different oils will not improve the performance or efficiency of the engine in any way. The additives in synthetic oil may have limited or no effect at all when mixed with a regular engine oil. Mixing different synthetic oil blends, on the other hand, may have negative effects in the long term as the additives may react. 

So, when you top up your engine oil after a leak, do not hesitate to mix oils if you do not get the same type of oil. In the long run, though, stick to using one type of oil to get the best performance out of your engine.