What happens if you mix regular oil with synthetic oil

If you’re a casual car owner you may not know the difference between synthetic and conventional oils. If you’re a more serious auto enthusiast you may know the differences and have a preference, but wonder about switching, mixing, or the benefits of your current preference. It’s important information for every car owner and auto enthusiast to understand, as it improves your car’s function and performance.

Table of Contents Show

Will mixing synthetic with conventional oil cause a gel to form?
Mixing Motor Oil
Possible Negative Effects
Difference in Regular and Synthetic Oil

Conventional oil is basic crude oil with simple additives to increase heat tolerance and improve lubrication. It’s cheaper than synthetic options, and it will get the job done if you’re a casual driver in totally normal conditions. Some people believe that conventional oil is much worse for the environment, despite it’s cost.
Synthetic oil, on the other hand, is a more complete package. Synthetic oils are designed to give the best possible lubrication and protection for your engine. They work much better than conventional oils, especially in very hot or very cold climates, or if you drive a high-mileage vehicle. Synthetic oil is generally accepted as the best possible choice for most cars, but it is more expensive than conventional oil. Not all cars require synthetic oil - consult your user’s manual and an expert to see if your car could benefit from synthetic oil use.

Now… can you mix conventional and synthetic oils?

There are a few reasons why people might want to mix conventional and synthetic oils. The most common is when you have some oil in your engine but you need more - and can’t find the match to whatever is already in your engine. For example you usually use synthetic oils, but you need to top it off and only have access to a conventional oil. Other people have tried to mix a cocktail of conventional and synthetic oils, trying to get the benefits of synthetic oils while decreasing the cost by adding conventional oils. Some people just mix oils without realizing that there is a difference between synthetic and conventional oil.

Technically the answer is yes, you can mix conventional and synthetic oils. Your car will not explode, seize up, or fail to run for you. If you absolutely need to mix your engine oils you can do that. Try your very best to get a flush and oil change as soon as you can, though. Mixing these oils is generally not the best idea.

Mixing conventional and synthetic oils will actually decrease the performance qualities you enjoy from synthetic oils alone. Conventional oils will ruin the cleaning and lubricating functions of the synthetic oils because their chemistry is completely different. They don’t necessarily work together like you think they would.

Switching to a synthetic oil could be a great option for you. Conventional oils may also work. Choose an oil that works best for your car and your needs and try to stick to it.

Remember to get regular oil changes and consider using an oil additive like CleanBoost EMT to increase the performance, lubrication, and engine efficiency of your car.

CleanBoost® EMT™

Will mixing synthetic with conventional oil cause a gel to form?

“I mixed Mobil 1™ with regular motor oil. My mechanic told me I should not do this because it forms a gel; is this true? I did it on three Honda Accords – a 2003 with 40,000 miles, a 1990 with 201,000 miles and a 1992 with 190,000 miles.”
Jordan Mayer, Cape Coral, Florida

Answer

In general, oils should be compatible with each other. It is not likely that you would form gel by mixing the two oils. However, we would not recommend mixing oils as a general practice because oils are complex mixtures of additives and base oils that can be destabilized. Also, why reduce the outstanding performance of Mobil 1™ synthetic motor oils by adding “regular oil”? Is it economics? You would be better to run all Mobil 1 synthetic motor and run it longer than mixing it with “regular oil.”

Not finding the answer to a question like yours?

Sappasit Wongkhonkan/EyeEm/Getty Images

Updated on January 10, 2020

Here's a practical chemistry question for you: Do you know what happens if you mix regular and synthetic motor oil?

Let's say the mechanic put synthetic oil in your car when you got your oil changed. You stop at a gas station and see you are running about a quart low, but all you can get is conventional motor oil. Is it all right to use the regular oil or will you risk harming your engine by doing so?

Mixing Motor Oil

According to Mobil Oil, it should be fine to mix oils. This manufacturer states it would be unlikely anything bad would happen, such as a gel-forming from an interaction of the chemicals (a common fear), because the oils are compatible with each other.

Many oils are a blend of natural and synthetic oils. So, if you are low on oil, don't be afraid to add a quart or two of synthetic oil if you are using regular oil or even regular oil if you are using a synthetic. You don't need to rush right out and get an oil change so you'll have "pure" oil.

Possible Negative Effects

It is not recommended to routinely mix oils because the additives in different products may interact or the oils may become destabilized by the mixture. You may reduce or negate the properties of the additives.

You could lose the benefits of the more expensive synthetic oil. So, adding regular oil to your special synthetic oil will mean you'll need to get your oil changed sooner than you would have otherwise.

If you have a high-performance engine, it may not allow the (expensive) additives to work the way they are supposed to. This may not damage your engine, but it won't help its performance.

Difference in Regular and Synthetic Oil

Both conventional and synthetic motor oils are derived from petroleum, but they can be very different products. Conventional oil is refined from crude oil. It circulates through the engine to keep it cool and prevent wear by acting as a lubricant. It helps prevent corrosion, keeps surfaces clean, and seals the engine. Synthetic oil serves the same purpose, but it's tailored for higher temperature and pressure.

Synthetic oil is also refined, but then it's distilled and purified so that it contains fewer impurities and a smaller, select set of molecules. Synthetic oil also contains additives intended to help keep an engine cleaner and protect it from damage.

The main difference between regular and synthetic oil is the temperature at which it undergoes thermal degradation. In a high-performance engine, regular oil is more apt to pick up deposits and form sludge.

Cars that run hot do better with synthetic oil. For most automobiles, the only real difference you'll see is that synthetic costs more initially but lasts longer between oil changes.