Can You Mix Fully Synthetic With Semi Synthetic Oil? 

can you mix full synthetic with semi synthetic

Can you mix fully synthetic with semi-synthetic oil? This is a question that many people ask. To answer this question, it’s important to know the difference between fully synthetic and semi-synthetic oil. Also, one point needs to be clarified here: what does “fully” or “semi” mean?

There are many myths and misconceptions about mixing engine oils, but it is important to remember that they’re not inherently bad. In this article, we’ll discuss if you can safely mix fully synthetic oil with semi-synthetic oil.

Can You Mix Fully Synthetic With Semi-Synthetic Oil? 

The short answer is yes. You can mix fully synthetic with semi-synthetic oil. However, you should check the viscosity, certifications, and brand when you have to mix the two. We highly discourage mixing synthetic and semi-synthetic oil, but it could be a better alternative if you are running low on oil and that is the only option.

There are other circumstances where you may mix fully synthetic with semi-synthetic oil. For example, you can mix a 10w50 synthetic with a 10w50 synthetic blend because you have a leftover bottle of either oil that you would like to use.

However, mixing your full-synthetic 20W-60 motor oil with synthetic blend 5W30 could result in unpredictable properties and results under different driving conditions. Although the effect might not be observed immediately. The same goes with mixing two different brands of engine oil.

Each oil brand closely guards its proprietary chemical formulas as a trade secret, with promises to protect longer, better, and across a wider range of environmental conditions (source Forbes).

In summary, mixing synthetic and semi-synthetic oil degrades down to the lesser quality of the two oils. You will no longer have all of the benefits from pure synthetic oil, which is why it’s best not to mix them unless in an emergency. If you have to mix the two, make sure to change your oil with the specified engine oil on the owner’s manual.

Related: Can I Use 10w30 Instead of 5w30? 10w30 vs 5w30 Engine Oil

Can You Mix Synthetic with Conventional Oil

Likewise, you can safely mix synthetic and conventional oil. In fact, synthetic-blend motor oil is simply conventional and synthetic oil already mixed for you.

So what’s the difference between them? The main point is that you can’t just buy any ordinary synthetic oil and mix it with conventional motor oil. According to Mobil, not all synthetic oil is created equal.

Synthetics are formulated differently. One minor change in the formulation can have a major effect on performance, for example, if you add more of one additive to the synthetic it will make it better at cleaning but worse when cold outside and vice versa.

Related: Can you mix 5w20 and 5w30 engine oil? Read First

Synthetic Oil vs Semi-Synthetic vs Conventional

Conventional or Mineral

There are a few different types of motor oil you can choose from, but conventional oils seem to be the most popular and recommended for use in engines with moderate mileage. These often come with lower prices as well which ultimately makes them more cost-effective when it comes down to keeping your engine lubricated.


Synthetic oil offers a uniform, high-performing viscosity that is perfect for any type of weather and driving conditions. The result? It will always provide sustained performance no matter what the climate or your workload may be.

Synthetic motor oil lasts longer than any other type of oil because it’s made with advanced technology that resists breakdown and sludging. This saves you trips to the mechanic, so your car is always in top shape!


Semi-synthetic oil offers better protection than conventional oil but at a lower cost. This makes it the perfect middle ground for people who want to get some of the benefits that either type can offer without paying top dollar! Semi-synthetic is usually recommended for vans and trucks operating under moderate driving conditions.

Related: Can You Mix 5w30 And 5w40 Oil? Yes But Not Ideal

Why you should use fully synthetic engine oil

The beauty of fully synthetic oils is their longevity and durability. With a lifespan as high as 250,000 miles or more, you’ll be able to reap the benefits of this innovative product for years without any worries—even at both low and high temperatures.

Unlike most conventional oil products that break down quickly with time, fully synthetic oils will retain viscosity in all conditions due to their stable molecular structure.

A lot of people use synthetic blends or semi-synthetic oil because they are cheaper than fully synthetic and deliver better benefits than conventional or mineral-based oil. It’s important though that these oils do not last as long or provide protection from catalytic converter clogs as full-synthetic does.

Read more: Clean vs Dirty Engine Oil Comparison


You can mix synthetic and semi-synthetic oil, but it’s best not to. If you do have to mix the two oils, make sure to change your engine oil as specified by the owner’s manual for that particular car or truck.

Synthetic oils are superior in quality because they offer better protection against sludge build-up than their cheaper counterparts; mixing them might degrade down into a lesser quality of either one.

Engine oil is probably the most crucial aspect of vehicle maintenance you should keep your eye on. To know more about car repair and maintenance tips, follow our Facebook page.

If you want to know if it’s safe to mix two different viscosity, such as the 5w30 and 5w40? Read the answer here.

Elevate your car maintenance game by reading our comprehensive guide on engine oil. Learn everything from the basics of oil types, to how to properly maintain and change it. Keep your vehicle running at its best, read our guide now!

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