Engine Oil Grade Ratings Overview

An engine’s manufacturer typically specifies a particular type of oil or sets a minimum requirement for its usage. However, you might be curious about the variations in oil weights, grades, and viscosity. For instance, you might be wondering about the difference between 5W-30 and 10W-30. This article will provide all the necessary information about these numbers. While engine oil is generally the same, there can be exceptions to the rule of following the manufacturer’s recommendation. For instance, in the case of an older engine or when the vehicle’s parts have larger clearance between components, thicker oils can enhance performance. Nonetheless, it is best to adhere to the manufacturer’s recommendation unless such circumstances apply.

Types of Engine Oil

There are three types of Engine Oil:

  • Mineral Oil. Derived from petroleum products, undergoes treatment to function under a diverse range of temperatures and is usually preferred by older models of cars. Due to its low oxidation stability, mineral oil must be changed frequently. This oil is cheaper than other varieties. However, it is not the best quality.
  • Semi-synthetic Oil. This oil is suitable for high-performance vehicles. The oil change period is longer than synthetic oils for diesel and petrol engines. Therefore, synthetic engine oil provides the best protection for most driving conditions.
  • Synthetic Oil. This oil goes through comprehensive treatment in the laboratory. In this process, mineral oil is broken down into its basic constituents. As a result, they are significantly superior to their competitors. This also helps to remove any impurities to a very large extent. Synthetic oil molecules are also consistent in their size and shape, offering superior lubrication—full synthetic oil functions at its optimum in low or high temperatures or under extraordinary stress.

Understanding the Oil Codes

The terms weight, grade, and viscosity are often used interchangeably to refer to how easily oil flows and how thick it is. For instance, many vehicles use multi-grade 5W-30 oil. The first number followed by “W” indicates the viscosity in cold weather. As the number decreases, the oil becomes thinner and less viscous at lower temperatures. The second number indicates the viscosity in hot temperatures, with higher numbers indicating thicker oil at optimal temperatures. Older car models used different oil weights for different seasons, but this practice is less common due to lighter engines and different engine materials. It is always recommended to follow the manufacturer’s fluid specifications outlined in your vehicle’s manual. Using oil weights other than those recommended may reduce fuel economy or increase engine wear.

Grades of Engine Oils

Motor oil is graded based on its viscosity by the society of automotive engineers.

  1. 0W-20 – This oil is thinner when you start the engine. In 0W-20, the oil’s viscosity is 0 when the engine is cold. However, when the engine reaches its normal operating temperature, the oil’s viscosity becomes 20.
  2. 0W-30 – Is engineered to behave as a 0-weight oil at the starting temperature and a 30-weight oil when the engine reaches its average operating temperature.
  3. 0W-40 – Is engineered to behave as a 0-weight oil at the starting temperature and a 40-weight oil when the engine reaches its average operating temperature.
  4. 5W-30 – Is the most extensively and commonly used engine oil.
  5. 5W-40 – Is a fully synthetic engine oil that performs like a 5-weight engine oil when experiencing a cold start. Once it reaches normal operating temperature, it acts like a 40-weight oil.
  6. 10W-40 – Offers a 10-weight performance in cold starting temperatures. The engine’s normal operating temperature, however, provides a 40-weight performance.


Manufacturers often provide a variety of engine oil types suitable for different climates. Regularly changing your car’s oil and using the correct grade are crucial preventive maintenance tasks for your vehicle. Failure to perform these tasks may lead to an engine seizure caused by oil depletion, which can be very costly to repair. Most issues related to poor oil management are avoidable with proper maintenance. Investing in good automotive service practices is the best way to avoid hefty repair bills in the future. Knowing the correct oil to use is an excellent first step toward taking care of your engine and ensuring your vehicle runs smoothly.