Choosing the right engine oil is essential for proper engine lubrication. Engine oil is classified into three types: conventional oil, synthetic blend oil, and fully synthetic oil. A synthetic blend is a mixture of conventional and fully synthetic oil.

You may wonder if it is possible to mix synthetic and blended oil. The short answer is yes. However, a few things to keep in mind while combining the two oils. Let us go through this in detail in this article.

What Happens When You Mix Synthetic Oil and Synthetic Blend Oil

As we all know, a synthetic blend combines conventional and synthetic oil. Because different types of lubricants have the same base, they will blend properly without causing any negative effects. Synthetic blends are usually composed of 30% fully synthetic oil and 70% conventional oil. 

The concentration of synthetic oil in the synthetic blend will increase as you add more. This will improve the lubrication since synthetic oil is of higher quality. However, the benefits of fully synthetic oil will be reduced due to the presence of conventional oil in the synthetic blend.

Can You Mix Full Synthetic Oil With Blended Oil?

Yes, you can mix synthetic oil with a synthetic blend. This will not have any detrimental effect on engine oil lubrication. Synthetic blend oil is gaining popularity since it is less expensive than synthetic oil while maintaining almost the same quality and additives.

So combining synthetic oil with synthetic blend oil is normal and will not affect lubrication. Rather, it can extend the life of engine oil and boost performance at high temperatures.

Factors to Keep in Mind When Adding Synthetic Oil to a Synthetic Blend:

1) Viscosity: Check the viscosity of the synthetic oil you use. If the viscosity grade of the synthetic oil is different, it might impact engine lubrication. The viscosity index of a synthetic blend oil can be reduced by combining a 5W-30 synthetic oil with a 10W-40 synthetic blend oil.

As a result, the final combination will be thicker than 5W-30 but thinner than 10W-40. Although this will not significantly impact you, you can notice issues when driving at extreme temperatures.

Unless there is an emergency and the oil level is dangerously low, it is advised that you top up the oil with a similar viscosity grade. Check the owner’s manual for your engine’s recommended viscosity of the oil.

2) Brand: When topping up, it is recommended that you use the same brand of oil. This is because each manufacturer has its methodology for adding additives in varying concentrations. 

When the oil is changed, some old oil remains in the pan and mixes with the new engine oil. So, if the old oil in the engine is approximately 15-20%, adding oil from a different brand will not have a severe effect.

It can be concerning if the concentration of lubricants from different brands is split around 50-50. When two different brands of engine oil are mixed, additives react and can reduce the age of the engine oil. Therefore, it is always advised to add synthetic oil from the same brand to your synthetic blend.

Which Oil is Better: Synthetic Blend or Full Synthetic?


synthetic blend is significantly less expensive than synthetic oil. This is because it is mainly blended with conventional oil, which is much cheaper than fully synthetic oil. Different brands use a different proportion of synthetic oil in their blend. The more synthetic oil in a synthetic blend, the more expensive it is.


Fully synthetic oil is the apparent winner in performance and quality. They will perform better at extreme temperatures, last longer than synthetic blends, and offer the best lubrication. While synthetic blends can only go 5,000–7,500 miles, fully synthetic oil can last for about 10,000–15,000 miles.


Synthetic oil performs better at high temperatures and properly lubricates engine parts.Fully synthetic oil is slippery and can damage seals and gaskets in older vehicles. Switching back to normal oil is not suggested since it might create leaks and other problems in the engine.

Yes, synthetic oil can be mixed with conventional oil. This, however, reduces the performance and benefits of fully synthetic oil. This sort of combination is already well-known in the market as a semi-synthetic or synthetic blend. It is important to consider the proportions of synthetic oil and regular oil to be blended according to your requirements.

You will notice that a synthetic blend does not last as long as fully synthetic oil. Synthetic blends are less expensive and function better in older vehicles. However, fully synthetic oil can perform better in extreme temperatures and give better wear and tear protection if you have a high-performance vehicle.


In conclusion, you can mix synthetic blends with fully synthetic oil. Oil will mix easily and won’t hurt the overall lubrication of the engine. The benefits of fully synthetic oil can be reduced due to the presence of conventional oil in a synthetic blend. Still, the engine oil will perform better when the concentration of synthetic oil in the synthetic blend increases. 

Make sure the oil you add is of the same brand and viscosity. Excess synthetic oil can also harm seals and gaskets in older cars. Therefore, be sure to add synthetic oil correctly and suit your needs.

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