Can I mix different grades of engine oil?

There are different types of oils for various vehicles, which operate uniquely in varied conditions. Motor oils have different grade ratings based on different factors. These grade ratings determine their viscosity and performance in various weather conditions.

Some people mix different grades of engine oil due to lack of their regular motor oil or in a bid to switch to another brand with a different grade. Therefore, is it possible to mix different grades of engine oil?

Can I mix two types of engine oil?


It is unlikely for anything terrible to happen when you mix two different types of oil. Generally, engine oils are a combination of synthetic and natural oils but may differ when it comes to additives. As such, these oils are highly compatible.

By mixing two different types of engine oil, there is no production of unwanted byproducts; thus, engine performance will not have any immediate changes. Car owners who reside in areas with extreme climatic changes usually switch from mineral oil to synthetic oil as the seasons change.

Mixing synthetic engine oil with regular oil may have limited or no effects. However, by combining two different brands of synthetic engine oil, the additives in both oils may react, negatively affecting your engine in the long run

Mixing two engine oil viscosities

Engine oil viscosity refers to the nature of the oil and its performance at specific temperatures. Thin oils have low viscosity, ideal for cold temperature, while thick oils have high viscosity levels, perfect for high temperatures.

mixing different engine oils

Therefore, it is essential to consider the location where you intend to drive in and its average weather conditions when choosing the best motor oil for your engine.

According to the scale developed by the Society of Automotive Engineers, engine viscosity is denoted using ‘XW-XX,’ with W referring to winter and XW indicating viscosity at 100°C. It also represents the resistance of oil to thinning at high temperatures.

The mixing of two similar brands and types of oil, but with different viscosities, is not harmful to your engine, as long as you do not mix them equally. By combining them, you may not be able to predict the exact viscosity of the resultant oil, but it will be useful in lubricating your engine’s moving parts.

Often, the mixing of two different oil viscosities occurs when drivers are on a long-distance drive, and they need to top-up their motor oil. Mixing two different oil viscosities is, however, not recommended for an entire oil change interval.

Can you mix 5W-30 AND 10W-30?

Many cars and trucks use multi-grade oil, such as 5W-30 and 10W-30. These oils can start your engine at both cold and normal temperatures of about 210˚F, without compromising your engine’s efficiency. Multi-grade oils become thinner in cold weather to provide adequate protection to the engine as it warms up.

The first number in the viscosity grade indicates low temperature; in this case, it is 5W and 10W. The other figure in the viscosity grade refers to the high-temperature rating (i.e., 30). When deciding whether to mix these multi-grade oils, it is best to consider the temperatures of where you reside and your engine’s age.

5W-30 oil is reliable in both low starting temperatures (30˚C) as well as hot summer temperatures (35˚C). This multi-grade oil creates less drag on the moving engine parts and bearings, hence its high level of fuel efficiency.

10W-30 oil is much thicker than 5W-30; therefore, it is better suited for older vehicles and trucks. This oil provides better sealing capabilities required by older engines; hence, better protection of the engine’s moving parts. This particular oil performs best at temperatures above 18˚C and below 30˚C.

Mixing engine oil brands

Mixing different engine oil brands as a result of topping-up your oil level does not cause any irreparable harm to your engine. Made from different companies, engine oil has a distinct chemical make-up, thus, mixing two brands for an entire oil change interval is not recommended.

mixing two different engine oils

Each brand of engine oil has different additives with different roles. Mixing synthetic engine oil with regular oil may have limited or no effects.

However, by combining two different brands of synthetic engine oil, the additives in both oils may react, negatively affecting your engine in the long run. Check your user manual for the best type of oil that is ideal for your vehicle. 


Good quality motor oil should efficiently lubricate moving parts in the engine and provide immense horsepower, thus prolonging its entire lifespan. Motor oil manufacturers take a lot of time to balance out the chemicals in their products.

Distorting this balance is not advisable as it may not bring about the results you want. Luckily, even though you mix different oils, it does not cause any wear and damage to your engine, as long as the oils are of similar brands.

Oils are miscible liquids, meaning you do not need to mix them in a particular proportion as they will easily mix.

However, it is best to stick to one grade of engine oil to avoid detrimental damage to your engine. Their unique additives may or may not be compatible. If not compatible, they are highly reactive, which is dangerous for your car.

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