Can You Mix Synthetic Oil With Regular Oil?

mixing synthetic oil with regular oil
08th Jun,2022

There are some rules set in stone when it comes to our cars. When not followed, there may be some negative implications to the performance and the engine itself. For example, putting diesel into a gasoline engine clogs filters and causes cylinder issues, ultimately leading to engine failure. But what about mixing synthetic and regular oil? Can you mix engine oil and have no harm done?

This article will serve as your complete guide to the question of mixing synth oil with regular oil. After you’ve finished reading this post, your search for answers will have been done.

So, can you mix synthetic oil with conventional oil?

To give a straightforward answer, yes you can mix synthetic with regular oil. If you’ve already done it and you want to know if it will harm your engine, you can breathe now because your engine won’t break down. However, there are some things you should know.

First off, synthetic and conventional motor oil have very different formulations. As you probably know, synthetic oil is significantly higher in quality compared to regular. Although both of them have your general base oils and additives, synthetic oil is bereft of the impurities found in regular oil. They also have a higher viscosity rating and are so much better at handling extreme temperatures. In short, synthetic oil is just on an entirely different level compared to conventional oil.

Generally, there’s no real danger when mixing these two types of products. However, mixing them in the right amounts is a must in order to avoid negative effects on your engine. The only catch is that the benefits of synthetic oil will be lessened when combined with conventional oil. Let’s explore this point further.

Why mixing synthetic and conventional oil is not a good idea

While it’s been established that synthetic oil and conventional oil can be mixed, it’s really not a good idea.

One of the reasons is that they are formulated differently. Motor oil products have different additives infused in them, which, when combined, may interact and get destabilized. It’s similar to the rule that there are some medicines you shouldn’t take together. Synthetic and conventional oils don’t really work well when mixed.

When a full synthetic oil is combined with a conventional one, you’re diluting the performance and benefits of the synthetic oil you’re using. Like previously mentioned, synthetic oils are superior lubricants, cleaners, and performance-boosters for any engine. So while it’s technically safe to mix, you’ll be reducing how your vehicle operates at its optimum level. You shouldn’t notice any weird smell when you make the mixture but if you do it is likely due to something gas in your oil. 

So unless it’s an absolute emergency, don’t mix conventional oil and synthetic oil even if you can.

Why People Mix Synthetic With Conventional Oils


If you travel frequently especially long distances, you may have experienced this already. You’re driving and realize you’re running low on oil, so you head to the nearest gas station to buy the lubricant you need. The thing is, they only have conventional motor oils in stock. They don’t sell the high-quality synthetic oil you use in your car. In that case, there’s no other option but to mix the oils. Your focus at the moment is to not run out of oil. If this is the case, then it’s fine. Just schedule an oil change sooner rather than later.


It’s a common misconception that the answer to a performance boost is by using two types of oil. Does adding some synthetic to your conventional oil enhance performance? Not really. 

If you’re using conventional oil, the ratios must be precisely right in order to notice a change. But if you’re using synthetic, there’s absolutely no reason why conventional oil should be added for the sake of performance because you are already using the right product.


Synthetic oils are expensive whereas conventional oil is cheap. This is one of the most common reasons why people mix them together — in order to save money. But note that synthetic oils provide great engine protection, superb cleaning, and increased engine life overall. If you’re mixing synthetic oil with regular oil for the purpose of saving money, you’re not really fulfilling that purpose since you’re damaging the engine in the process. If you really want to save, use a great quality synthetic oil and enjoy its long-term benefits. 

When should you mix synthetic oil with conventional oil?

Low on oil

In cases when you need to use whatever is available, then you can combine these two oils. What’s important is to not let your vehicle run out of oil.

Switching oils without flushing

Only do this if your engine is not due for a flush. But in essence, you’re technically mixing new oil with the residue of the old one when you’re changing the oil without flushing. 


Some things about cars can be tricky, including the dilemma of mixing two types of oils. Just to emphasize our answer to the question, synthetic oil and conventional oil are safe to mix, but it’s generally not a good idea. Avoid doing so if possible, and mix them only when absolutely necessary. 

William Johnson

William Johnson is the owner and founder of He writes about car accessories, with his passion stemming from a deep enthusiasm for all things automotive. His website, RRD, focuses on in-depth reviews of car accessories to help people find the best and latest products in the market.