All About Mixing Different Engine Oils in Your Car

all about mixing different engine oils

  • Engine Types
  • Mix Two Different Engine Oils
  • Consequences of Mixing Engine Oils
  • FAQs

Your vehicle’s engine is a complex piece of machinery that requires proper care and maintenance to ensure optimal performance and longevity. One crucial aspect of engine care is choosing the right engine oil and sticking to a consistent maintenance schedule. However, there may be instances where you find yourself needing to top up your engine oil and you may wonder if it’s acceptable to mix different types of engine oils. Let’s explore the potential consequences of mixing different engine oils and why it’s generally not recommended.

Types of Engine Oil

You should avoid mixing different engine oils in a car
It is not recommended to mix different engine oils in a car

There are different types of car engine oil, each tailored to specific needs and conditions. Understanding the distinctions is crucial for optimal vehicle maintenance. Here are the primary types of engine oils:

Mineral Oil

Characterised by high viscosity, mineral oil is more prone to deterioration when exposed to elevated temperatures. While effective in certain conditions, its limitations make it less suitable for high-temperature environments.

Semi-Synthetic Oil

With additional additives for enhanced performance, semi-synthetic oil strikes a balance between cost-effectiveness and improved heat resistance. This type of oil is also used for its versatility and ability to provide better protection in various driving conditions.

Synthetic Oil

Often labelled as ‘fully synthetic,’ this oil type boasts superior properties, maintaining its effectiveness even in extreme temperatures. Known for a longer lifespan compared to other types, synthetic oil is a top choice for those seeking optimal engine protection and performance longevity.

What Happens If You Mix Two Different Engine Oils? 

causes of mixing different engine oils in car
Thin oils with lower viscosity are preferred for facilitating cold starts when mixing different engine oils in a car

Mixing engine oils generally won’t damage your engine, but closely matching viscosities is crucial. Here are key points to consider:

  • Viscosity Basics: The left-hand number (5W or 10W) plays a pivotal role in indicating viscosity. It dictates the thickness of the oil at different temperatures.
  • Cold Starts vs. High Temperatures: Thin oils with lower viscosity are preferred for facilitating cold starts, while thicker oils offer superior protection in higher temperatures. The ‘W’ in the oil grade stands for ‘winter,’ indicating the oil’s performance in colder temperatures

Understanding viscosity is paramount to achieving a harmonious blend of engine oils and ensuring optimal engine performance. Besides, here is a detailed overview of how car engine oils work.

Mixing Different Brand Oils

Mixing engine oils from different brands introduces a potential risk. This risk arises from the diverse production methods and proprietary additives employed by manufacturers. Consider the following points when mixing different brands of engine oils in a car:

  • Risk Factor: Mixing introduces the potential for oils with different physical properties, posing a risk to engine health.
  • API Certification: While some argue that mixing is acceptable if both oils are API-certified, caution is advised.
  • Preventive Measure: Undertaking an oil change promptly after mixing is recommended to prevent potential long-term damage and avoid the risks of delaying an engine oil change.

Specific Case: 5W-30 and 10W-30 Oils 

The mixing of 5W-30 and 10W-30 oils is generally considered a safe practice due to their close viscosities. Consider the following:

  • Viscosity Variation: Before mixing 5W-30 and 10W-30 oils, consider the density difference.
  • Temperature Consideration: The left-hand number indicates viscosity at lower temperatures, with 5W-30 being thinner and more effective in colder weather.

For more understanding, also read on the difference between 0w30 vs 5w30 engine oil.

Consequences of Mixing Engine Oils

you must know What happens if you mix 2 different engine oils
You must consider the consequences of mixing different engine oils in a car

Here are some consequences you might face after mixing different engine oils.

Viscosity Issues

Engine oils come in various viscosity grades, such as 5W-30 or 10W-40, indicating their flow characteristics at different temperatures. Mixing oils with different viscosities can also result in an inconsistent oil flow, potentially compromising engine lubrication and causing increased friction.

Additive Compatibility

Engine oils often contain additives that enhance their performance. Mixing oils from different brands or formulations may lead to incompatible additives, reducing the overall effectiveness of the oil. This can also impact the oil’s ability to clean, protect and cool the engine.

Chemical Reactions

Different engine oils may use different base oils and additives and mixing them can trigger chemical reactions. These reactions may also produce sludge, deposits, or other harmful substances that can accumulate in the engine, leading to reduced efficiency.

Reduced Performance

The primary goal of using engine oil is to ensure smooth engine operation. Mixing oils can compromise this objective, resulting in reduced fuel efficiency, increased emissions and a decline in overall engine performance.

Warranty Voidance

Some vehicle manufacturers specify the type of oil that helps in maintaining warranty coverage. Also, mixing different engine oils may void the warranty, leaving you responsible for any potential repair costs.

To enhance fuel efficiency, always use the appropriate engine oil. Here are some indicators that you might be using an incorrect engine oil.


Is it bad to mix 2 different engine oils?

In general, mixing two different engine oils won’t harm your car’s engine. However, if you plan to do so, try to closely match the viscosity of both oils. Viscosity is crucial as it determines how well the oil works at different temperatures.

Can you mix 10W-40 oil with 5W-30 oil?

Yes, you can mix them, but the resulting viscosity will be in between the two. The exact level depends on the ratio of one oil mixed with the other. For example, adding a quart of 10W-40 to an engine with 5W-30 should be fine.

That is all about mixing different engine oils. However, it’s crucial to adhere to your vehicle manufacturer’s recommendations regarding engine oil type and viscosity. While topping up with a different oil in an emergency might not cause immediate catastrophic damage, it’s not a practice to adopt regularly. Here are some benefits of a regular oil change to ensure the longevity and optimal performance of your vehicle’s engine.

Also, it’s best to stick to a consistent oil type and brand, following the manufacturer’s guidelines. Also, make sure you avoid these misconceptions about car engine oil and get optimal performance.

If you are planning to buy used cars for sale in the UAE, make sure you change oil regularly. Regular oil changes yourself and proper maintenance will go a long way in preserving the health of your engine and preventing unnecessary complications.

Stay tuned to the dubizzle car blog for more car engine maintenance tips.


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