Difference Between Synthetic, Mineral and Semi-Synthetic Engine Oils - A Complete Guide

Engine oil is the lifeblood of a vehicle's engine. Although it has many functions, engine oil is mainly used for the lubrication of the engine and its components. It reduces friction between moving parts inside your vehicle’s engine and is the most important thing that is replaced during the vehicle’s service. It keeps the engine and its components lubricated, prevents friction, and cools the engine to ensure smooth and efficient functioning.

There are different engine oils to choose from, each having its own characteristics and pros and cons. Read on to learn about the basics of engine oil, the difference between mineral, synthetic, and semi-synthetic engine oil, and what factors you need to consider before purchasing engine oil for your car.

In this article:

5 Functions Of An Engine Oil

1. Lubrication

As mentioned at the start, the most important function of engine oil is lubrication. Engine oil or motor oil lubricates the moving engine components of an internal combustion engine. This minimizes engine wear and increases the service life of your vehicle’s engine.

2. Cooling

As the engine works continuously, it generates a lot of heat. This heat is carried by engine oil and released through lubricant passages. Engine oil supplements the coolant for this purpose. Interestingly, engine oil is responsible for 30- 40% of your engine’s cooling process.

3. Acid Neutralization

During the burning of fuel, the oxidation of other lubricants and fuel forms acids. These corrosive acids can damage metal parts in the engine. Modern engine oils have additives in them that neutralize these corrosive acids.

4. Cleaning

When your vehicle’s engine runs, it creates impurities such as sludge, dust, dirt, metal particles, and acids. Without engine oil, these residues would clog the engine and decrease its performance. Engine oil suspends these impurities and circulates them continuously to the oil filter to remove them from the engine block. Thus, engine oil cleans the engine block and prevents damage and engine wear.

5. Sealing

Engine oil ensures engine sealing, especially for pistons and cylinders. It prevents leaks through microscopic gaps between the piston and cylinder. Thus, it enhances your vehicle’s engine performance.

4 Types of Engine Oils

All engine oils are formulated with base oils that are obtained through raw oil refining. These engine oils are treated with chemicals, additives, dispersants, and detergents to enhance their characteristics. These factors determine the properties of engine oil and how it will perform across changing temperatures. Therefore, it is necessary to know about different engine oils, so you can make wise decisions and improve your engine's health. Some types of engine oils are discussed below:

1. Mineral Or Conventional Engine Oil

Mineral engine oil, also known as conventional engine oil, is the simplest form of motor oil that is achieved by refining the crude oil in the factory. It then undergoes several processes, and additives are added to improve its viscosity and lubrication properties. Mineral oils are treated to operate over a wide temperature range, making them ideal for general commuting conditions. Many automakers still recommend conventional motor oils, provided they comply with the latest industry standards.

2. Fully Synthetic Oil

Synthetic or full-synthetic engine oils are man-made oils manufactured in the lab and chemically engineered and refined for better performance. Compared to mineral oils, synthetic engine oils comprise more additives, like corrosion inhibitors, anti-wear additives, and detergents. Synthetic engine oils are broken down and refined at molecular levels to remove impurities, making them more stable and long-lasting compared to mineral oils. Because of controlled manufacturing, fully synthetic oil offers high viscosity, corrosion, and oxidation resistance. Due to all these qualities, it is expensive and is recommended for high-tech engines and heavy-duty vehicles.

3. Semi-Synthetic or Synthetic Blend Oil

Semi-synthetic motor oil is a mix of synthetic and organic base oils and is formulated to provide protection for moderate to heavy engine loads and high temperatures. It is a great option for those who want extra performance at a price just a little above conventional oil. Semi-synthetic oil is recommended for SUVs or pickups for extra protection during activities such as hauling heavy loads.

4. High-Mileage Oil

If your car's odometer shows over 120,000 kilometers or your old car begin to show signs of engine loosening, then you should consider high-mileage oil. High mileage oil is loaded with special additives to take care of older engines, like conditioners, seal swells, antioxidants, detergents, and wear or friction additives that protect seals, prevent oil leaks, and reduce engine smoke and emissions. Usually, they use a viscosity modifier that is durable and won’t lose viscosity quickly.

After long usage, any mechanical device begins to loosen. As your car’s engine ages, seals, gaskets, and non-metal parts deteriorate. The higher-mileage oils are chemically engineered with seal conditioners that increase elasticity and restore shape.

Mineral Engine Oil
Synthetic Engine Oil
Semi-Synthetic Engine Oil
Natural and made from refining crude oil
Man-made and chemically manufactured in a lab
A mixture of synthetic and mineral base oils
Affordable compared to semi-synthetic and synthetic engine oils
Expensive compared to semi-synthetic and mineral engine oils
Affordable and formulated to offer the best of both mineral and synthetic oils
Breaks down at high temperatures
Specially engineered for better performance at high temperatures
Offers good lubrication during moderate to heavy engine loads
Inferior lubrication properties offer less protection at extreme conditions
The superior formulation offers best lubrication and makes parts less susceptible to wear
Average lubrication properties make it a better all-round choice for medium to extreme temperature conditions
Frequent replacement interval (approx 4500-5000kms)
Longer replacement interval (approx 7500 to 10,000kms)
Moderate replacement intervals (approx 5000-7500kms)
Can lead to sludge and scaling deposits on the engine
Leaves no or minimal deposits behind, making it easy to clean sludge and scaling
With a blend of mineral oil and 30% or less synthetic oil, it performs better than mineral oil and leaves less sludge or deposits
Used mainly for engine break-in periods for better seating of parts
Great for high-end cars and normal vehicles due to its superior cold-weather starting characteristics
Low viscosity and low friction properties of synthetic blend engine oils offer improved fuel economy

Things To Consider While Purchasing An Engine Oil

Engine oil is a fluid that keeps your motor running smoothly. It allows the engine to absorb heat, lubricate moving parts, and cool itself in order to keep it as efficient as possible. While choosing the perfect engine oil for your car, you might encounter various technical terms, types of engine oils, brands, oil grades, viscosity types, prices, etc. All these factors can become overwhelming while selecting one for your vehicle. Here are a few things that you should consider while choosing the correct engine oil.

1. Type Of Vehicle

The first thing to consider before choosing an engine oil is the make and model of your vehicle. Today, modern cars are designed for performance and high efficiency. The engine on these vehicles has tighter tolerances and refined components. Consequently, newer engine oils have also been developed with advanced technologies dedicated to these engines. Although it's safe to go with the manufacturer's recommendations, it's advised to use semi-synthetic and full synthetic engine oils for performance and high-end cars.

2. Engine Oil Grade

Engine oil grades are classified based on oil viscosity. These viscosity grades are denoted by numbers on the engine oil packaging. Viscosity is the resistance to oil flow, and the more viscosity, the better the lubrication. However, this viscosity changes with temperature, and they have an inverse relationship. If the temperature of the engine increases, the viscosity of the engine oil decreases, and vice versa. Therefore, choosing an engine oil with low viscosity might perform well at low temperatures, but will lose its lubrication capabilities if the engine gets hot.

The viscosity of engine oil can be determined with the letter W and the numbers adjacent to it. For example, a 10W30 engine oil will perform better at cold temperatures compared to 20W50. Similarly, 20W50 will perform better compared to 10W30 at high temperatures.

3. Engine Oil Standards

Ensure the engine oil you are choosing has abbreviations like API and ACEA on the packaging. This means that the engine you are purchasing meets the requirements set by these organizations. American Petroleum Institute (API) classifies the product based on wear resistance, oxidation, and fuel economy. API uses two letters S and C for petrol and diesel engines, respectively. The letters after that indicate engine performance. The higher the letter is in the alphabet, the higher the engine oil quality. For example, SJ<SL>SN<SN Plus, etc. 

Similarly, ACEA classifies engine oil quality by a sequence of numbers and letters. The letters A denote engine oils for light-duty gasoline and diesel engines. The A/B category has 4 quality levels. C denotes light-duty gasoline and diesel engines with exhaust after treatment, and the letter E is assigned to heavy-duty diesel engines. 

These standards are a great way to choose the correct and safe engine oil for your vehicle. Currently, API ratings for engine oils are as follows:

For Gasoline Engines

  • SJ: for vehicles manufactured between 2001 and 2004

  • SM: for vehicles manufactured between 2004 and 2009

  • SN: for vehicles manufactured after 2010

For Diesel Engines

  • CH-4: 1998 to 2002

  • CI-4: 2002 to 2010

  • CJ-4: 2010 to present

Older API engine oil ratings like SH and SA are expired and should not be used. Using engine oils with current ratings ensures the engine oil is fresh and compatible with your engine.

What Is The Best Engine Oil For A Diesel Engine?

Whatever we have covered so far is general information about engine oils, but diesel engine oils need some extra attention. At a superficial glance, both gasoline and diesel engine oils have similar appearances. But diesel engine oils have more complex chemistry compared to gasoline engines. This difference is because of the differences in exhaust systems used in diesel engines.

Generally, diesel engine oil has a higher viscosity. Diesel engine oil is not recommended for petrol engines because it would struggle, especially the engine oil pump, to circulate the thick diesel engine oil properly.

Diesel engine oils have zinc dialkyl dithiophosphates (ZDDPs), which are very effective anti-wear and corrosion-resistant agents. The design of exhaust systems in diesel engines is compatible with this additive, but it would cripple the catalytic converter if used in petrol engines.

Diesel engine oils contain more additives than gasoline engine oils due to their more complex chemical chemistry. Diesel engines create more waste products than gasoline engines, especially soot (partially burnt fuel), which accumulates in the crankcase. The extra detergent additives in diesel engine oil remove these waste products properly. In gasoline engines, these additional additives could cause damage to pistons and seals, leading to a loss in fuel compression. As already suggested, first you check the owner's manual and then get a recommendation from a qualified mechanic to ensure that your vehicle gets what it actually needs.

Should I Switch To High-Mileage Engine Oil?

There are two main reasons for using high-mileage oils. The first is to switch when your vehicle reaches 120,000 kilometers. The second is to switch if your older vehicle has started showing symptoms of engine loosening. If you notice an oil leak, it’s a sign that you should consider using high-mileage engine oil. If you notice a louder engine sound and new rattling noises, high-mileage oil would be beneficial.

If there are no such issues, don’t switch your engine oil. Because high-mileage oils are generally not API licensed, it is better to wait until your vehicle’s warranty period is over before considering the engine oil switch.


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Yes, you can mix different types of oil together. Unless your owner’s manual specifically recommends using synthetic oil, there shouldn’t be any problem mixing synthetic and conventional oils together. This means if, in case of an emergency, you bought the wrong type of engine oil to refill, there’s no need to worry. However, it should be noted that mixing any other type of oil with full synthetic engine oil will reduce its performance.

Yes, in the context of thickness/viscosity, usage (high/low loads), and working condition (cold/hot). No, in the context of brand, because brand is more of a personal choice. Every vehicle engine has a specific recommendation on the type of engine oil to be used. Therefore, it is always suggested to first check your vehicle’s owner’s manual. There are many oil grades, and using the wrong oil could harm your vehicle’s engine.

The oil change interval depends on the type of engine oil, driving conditions, and the vehicle. Earlier, cars used to have a comparatively shorter engine oil change interval of about 5000 kms. Today, it's recommended to have your engine oil changed every 10,000 kms or at least once a year. However, if your car uses fully synthetic engine oil, it can have a higher change interval of up to 10,000 to 20,000 kilometers.

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John Framigllia
Technical Writer
Our technical writer is known for simplifying automotive parts and services. Intuitive with various vehicles and manufacturers, he knows how to simplify complicated problems.