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Can You Mix Oil Weights? (Complete Guide)

There are so many oil weights. It’s hard to tell the difference so you might wonder whether you can mix oil weights or not. We’ve all heard of people mixing oil weights. Does anything happen to your engine when you mix oil weights? Is it okay? Let’s find out. 

Can you mix oil weights?

You can mix oil weights but it is not recommended by most automakers. Many oil weights are compatible and acceptable to mix. It might not cause any damage to your engine initially but there are disadvantages in the long run. It is better to use the original oil unless there is no other option. 

Is it OK to mix oil weights?

It is okay to mix oil weights if you are doing it temporarily. It is better if you pick oil weights of the same viscosity levels and same brands. This way, the performance of your engine will be less likely to be affected. 

Different brands have slightly different methods of manufacturing the oil so it’s better not to mix the two brands. 

What happens if you mix oil weights?

Possible scenarios that can happen if you mix oil weights are given below –

Increase oil pressure to risky levels:

Different motor oils have different viscosity levels. So if you use a thick oil weight on a vehicle that uses thin oil, it will increase your oil pressure. 

This means that your engine is not lubricating properly which can result in engine failure. It can also cause harm to the components of your engine.

No changes or benefits:

Mixing different oil weights might not do anything at all. It will not benefit the performance or efficiency of your engine at all. If you are mixing synthetic oil with regular oil, the additives could have a limited positive effect. 

But the long-term effects are negative since the additives will react.

Reduced service life for the mix:

The mixture produced will have a shorter lifespan if you use it regularly. And the additives can react and break down into toxic products that can lead to corrosion and sludging. So if you have synthetic oil, it’s better to stick to it. 

Can you mix two different types of motor oil viscosity?

There are some people who have mixed two different types of motor oil viscosity to set their own oil viscosity. But it is not as easy as it looks. Only professionals can achieve this without any issues. If you do this without being cautious, you are risking your engine and its components. 

Hence, you should not mix two different types of motor oil viscosity

3 reasons why you shouldn’t mix two different types of motor oil viscosity:

3 reasons why you shouldn’t mix different types of motor oil viscosity are given below –

Manufacturing differences:

The viscosity levels are different for every type. It is meant to function for only the recommended engine. It is not possible to determine if it will function the same way or if it will be effective or not. 

The lifespan of the mixture is also unpredictable. 

Oil Viscosity:

As the oil viscosity is different, you might not be able to reach the end product you want. New engine oil is hard to create. Motor oil makers have the experience and ability required to create the correct balance of chemical additives. 

So unless you are a professional, it is better to not get in between it. 

Temporary solution:

You should only mix oil weights when you have no other option. Your engine could function just fine in the beginning but you can’t know for sure how it will be in other conditions. It might not act properly in high heat conditions. 

Can you mix motor oils of the same viscosity?

Mixing motor oils of the same viscosity is wiser than mixing two completely different grades of motor oils. For example, it is ok to mix 5W-30 oil with a 10W-30 oil since both of them are SAE 30 weight. Their winter weights are different but it is barely an issue. 

They will not function the same way but it will work fine. 

What do oil weight numbers mean? – Understanding oil weight

The viscosity of an oil is defined by two numbers. The first number ends with ‘W’. The ‘W’ in your oil descriptions does not stand for Weight. ‘W’ means Winter. The second number tells how the oil functions at normal operating temperatures. 

The lower the number, the more easily it will flow. 


This oil was specially engineered to function as a 0 weight oil in cold conditions but it can also function like a 20 weight oil after the engine reaches its full operating temperature. 


This low viscosity motor oil can replace 5W-30 or 10W-30. It is synthetic which enables it to enhance fuel economy. 


This type of motor oil can be used in both diesel and gasoline engines. It is a basic type of oil that can be used for regular engines in normal temperatures. You can use it in cars as well as pickup trucks. 

Some popular European vehicles use this oil such as Porsche and Volkswagen. 


As the name states, this motor oil can go from a low viscosity grade of 5 to a higher grade of 30. It can be used in both diesel and light petrol engines. 

They are recommended by automakers for vehicles such as passenger cars, vans, trucks, and SUVs. 


5W-40 oil tends to flow more easily in cold conditions. It is popularly used for American diesel pickup trucks. There are 5W-40 oils available for both gasoline and diesel-powered engines. 


5W-50 motor oil is mostly used in applications such as motorsport, rough driving, vintage classic cars, towing, and high operating temperatures. Many high-performance sports cars use this oil. It is ideal for driving conditions. 


This is great for vehicles that operate at high temperatures due to their increased viscosity. It flows properly and also maintains its viscosity to prevent components from touching. 

It is picked for race engines and other high-performance engines. 


This oil is mostly used for older models. If you want to use it for newer model vehicles, it must have 5W-30 recommended by the manufacturers. They are compatible with farm tractors, passenger cars, light trucks, and diesel trucks. 

Can synthetic and conventional oil be mixed together?

Synthetic and conventional oil can be mixed but there are some disadvantages. Both are designed for the same uses which is why they go through the same standards. 

Synthetic oil has better quality additives with better standards unlike conventional oil that focuses on reducing the cost. Although different, they can be mixed without causing any damage to your engine. But this can affect the performance of synthetic oil. 

It is completely okay to mix the two when you don’t have any other option but it is better to change the oil back to the original one as soon as you can. Your engine will work just fine but your performance levels might hamper. It will reduce the benefits that synthetic oil has to offer. 

Is it acceptable to mix gasoline engine oil and diesel engine oil? 

You can mix gasoline engine oil and diesel engine oil because it will not damage your engine in the short run. Your engine performance will remain the same and it is safe to use. Make sure the oil you use meets the acceptable specifications of your engine. 

Using the same brands will also be better for you.

You should check your original equipment manufacturer (OEM) before doing it. Check your manufacturer’s instructions before mixing the two. There are two categories, ‘CK-4’ and ‘SP’ where CK-4 stands for diesel oil and SP stands for gasoline motor oil. 

If the diesel oil has both CK-4 and SP in its specifications then it is acceptable to use in both diesel and gas applications. If the diesel oil only includes the CK-4 category then do not use it in gasoline engines. 

Can you mix 5W30 and 10W30 oil?

Normally, when you mix two different oils, it has a possibility of affecting your engine and its components. It can lower your engine’s performance since the oils have different weight ratings, they won’t blend. 

10W30 oil is used for engines that carry a lot of loads so it is essentially thicker in cold conditions. On the other hand, 5W30 is less viscous when cold. 

However, mixing 5W30 and 10W30 has not been known to cause any harm to your engine. The worst thing to happen is probably losing your warranty. Most manufacturers do not advise mixing different oils. If you lose your warranty, the cost of expensive repairs will fall on you. 

But if your warranty period is over, it’s fine to mix the two

Can you mix 5W30 and 5W20 oil?

Mixing 5W30 and 5W20 does not pose any harm to your engine and its components. They have different weight ratings with different additives but it is safe to mix. The internal engine components are designed to only work with 5W20 motor oil. 

There is a risk of engine damage but the chances are almost little to none. This is because, in the winter or cold weather, both 5W30 and 5W20 have the same thickness. 

However, that does not mean that they will turn into the same oil. They will flow in their ways. If you’re going to mix the two, it is better to mix ones of the same brand. As a result, the difference will be almost unnoticeable and might boost your performance. 

Nothing big will happen to your engine. But it is better to go back to your regular oil as soon as you can.

Final Thoughts:

It’s common to not find the original oil required during a road trip when you are using a different gas station. In that case or during an emergency, it is okay to mix oil weights. But it is highly advised against regular use since it can harm your vehicle in the longer run.