Do you know what’s going on under the hood of your car or truck? Even if you understand the basics of changing your oil to keep your car running well, you might not be aware of all the functions of motor oil. Also known as engine oil, the oil you put in your car serves multiple purposes. Keep reading to learn more about the main function of motor oil, including the functions, how often motor oil should be changed, and more.

What is the Main Function of Motor Oil

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What Does Motor Oil Do?

Historically, motor oil has been a base oil and additive mixture that was designed to lubricate the various parts of a vehicle’s engine. But modern motor oil does more than that. Synthetic oil can lubricate, clean, cool, reduce friction, reduce wear and tear, and minimize acid build-up.

Today, motor oil contains about 70-90 percent base oil that comes from either crude oil or natural gas. The additives makeup around 10-30 percent of the mixture and usually are antioxidants, detergents, viscosity index improvers, and so on.

Different Types of Motor Oil

There are a few common varieties of engine oil available, each with its own unique composition and purpose:

  • Synthetic motor oil, as mentioned above
  • Synthetic blend motor oil: a blend of synthetic and conventional motor oil that has good performance at low temperatures and better oxidation resistance
  • Conventional motor oil: does not have the same performance as synthetic motor oil but does meet basic API recommendations
  • High-mileage motor oil: specially formulated for cars over 75,000 miles; available in both synthetic blend and synthetic high mileage varieties

In addition to oil types, there are various viscosity parameters that you can find on the shelves. The viscosity is expressed by two numbers on the bottle, such as 5W20. The first number represents viscosity when cold, the other when hot. Depending on the type of engine you have, the vehicle manufacturer may have a recommended oil type and viscosity. Check the owner’s manual for more information.

Regardless of the kind of motor oil you decide to use in your vehicle, the functions are relatively the same.

The Functions of Motor Oil

Here is a look at the main function of motor oil, as well as some added benefits:

Minimizing Friction in the Engine

Motor oil is mainly used as a lubricant for the engine to minimize friction and damage between the parts of the motor. This is accomplished by the oil washing the parts and leaving between a slick film on all the surfaces.

Having motor oil stick to the engine and prevent friction is a huge advantage in areas where your car might suffer from a “cold start.” This doesn’t apply solely to low temperatures but also starting your car after a prolonged period of time, such as 24 hours. Cold starts are when the most damage to the engine occurs.

Cleaning Gunk

Lubricants do more than reduce friction. They also keep contaminants from adhering to the various engine parts. The solvency of the base oil is key in maintaining engine cleanliness.

Added dispersants and detergents are also important. The dispersants keep pollutants and debris suspended on the motor oil, thereby preventing the formation of sludge. Detergents prevent contaminants from sticking to hot parts, such as the piston rings and pistons.

Sealing the Engine

There are places in the engine where combustion gases can escape. The motor oil acts as a seal between places like the cylinders and piston rings to keep those gases within the combustion chamber. This maximizes engine output and horsepower.


Friction makes heat. Conversely, using motor oil to lubricate the moving components of an engine helps prevent friction and reduces the overall operating temperature. Lubricants can also absorb heat and disperse it to other areas, such as the oil sump.

Corrosion Protection

One of the major functions of motor oil is to prevent corrosion from occurring. Lubricating the motor does two things: neutralizes corrosive elements introduced to the engine during use and produces a barrier that keeps corrosive contaminants from damaging the parts.

This is all because of the additives in motor oil. Without additives, motor oil would not be able to do this.

Energy Transference

The nature of the oil makes it a wonderful medium for energy transference, especially when used in engines with variable valve timing (VVT) and hydraulic valve lifters. Oil pressure can help regulate how fast the valves in VVT engines open and close.

Dampening Shock

All those moving parts within an engine produce a certain amount of motion and shock. Motor oil softens the blows to the engine. Higher quality synthetic oils can also disperse the energy throughout the engine and prevent breaks and ruptures. By minimizing mechanical shock, you increase the lifespan of the motor and its functionality.

Why You Need to Change Your Motor Oil

The main function of motor oil is to protect your engine from damage and corrosion by lubricating the moving parts and reducing friction. Each time you turn on the vehicle, there are by-products from the internal combustion. Although motor oil contains detergents and dispersants that deal with these contaminants, they do build up over time. As these contaminants accumulate, they create a sludge that bogs down engine performance.

If you do not change the motor oil regularly, the dirt, grime, and sludge in the motor will start to negatively impact your vehicle. Do not let your car run out of engine oil, as this will cause the engine to grind, seize up, and then stall out. This causes a great amount of damage, too, and could ruin your vehicle.

Be sure to change the motor oil in line with the manufacturers’ recommendations, typically around every 10,000 miles. If you have a high mileage vehicle or older model, you may need to change your motor oil more often. However, there are other factors, such as the kind of oil you use and the driving conditions of your area.


What is the main function of motor oil? Since the parts of an engine are in constant friction while moving, motor oil works as a lubricant to reduce those fricative forces and cool down the engine to prevent damage. Additives have been added to the oil mixture to remove the contaminants that naturally build up over time. To keep your car going strong and continuously benefit from motor oil, make sure you are routinely changing out your engine oil.

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