Motor oil can be divided into two different types of components – base oil and additives. Base oil makes up most of a motor oil formulation (typically 70% - 90% of the formula, depending on the motor oil grade).
Base oil is derived from crude oil and refined to use in motor oil formulations. Depending on the amount of refining done to the base oil determines the properties and characteristics of the base oil. The refining process removes many impurities in the base oil such as waxy materials and sulfur. The amount of waxy materials, sulfur and viscosity behavior of the oil at lower and higher temperatures determines the quality or group of the base oil.
The properties of base oil groups are defined by the American Petroleum Institute. The better the qualities of the oil, the higher the group number and the better performance of the oil.
In comparing similar viscosity base oils, synthetic base oils will show improved performance over conventional base oil in the following ways:
But base oil isn’t the only thing that defines the performance of a motor oil. The remaining components of motor oil are the additives and viscosity modifiers of the formulation. These components play a critical role in protecting the engine. Viscosity modifiers change the viscosity or flow characteristics of the motor oil – allowing the oil to flow better at low temperatures and to help keep the oil thick enough at high temperatures to protect metals surfaces from contacting each other. And the additive package protects the engine in many ways, such as:
Viscosity is the resistance to flow of a fluid. Motor oil viscosity grades are based on a scale developed by the API (American Petroleum Institute) and are based on the resistance the oil gives to flowing at two different temperatures – cold and high temperature. The measurement of viscosity at high and low temperatures are properties of multi-grade oils.
The low temperature viscosity of the oil is a measurement that simulates starting a car on a cold winter day. That value has the letter “W” after the number and has a dash after the W. For example, if the oil is a 5W-30, the 5W part describes the viscosity of the oil at low temperatures. The lower the number, the faster the oil will flow at vehicle start up.
The high temperature viscosity is the number after the dash and is related to the viscosity of the oil as it is moving around your engine after the car has warmed up and is at normal engine temperature. In the 5W-30 example, the 30 defines the viscosity of the oil at normal engine temperatures. Again, the lower the number, the lower the viscosity of the oil and the faster the oil will move around the engine.
In recent years, lower viscosity oils are most often required by auto manufacturers. The key reasons for the need for reduced viscosity oils are engine design and fuel economy. Engine size has reduced over the years while delivering more power. The smaller size of these engines requires thinner oils to move through engine pathways to keep vital engine parts protected. And lower viscosity oils move easier which results in better fuel economy in vehicles.
Currently, 5W-30 and 5W-20 are the most popular viscosity grades required by vehicles on the road. But 0W-20 is the fastest growing viscosity grade and is likely to be the most popular grade required by vehicles on the road in the within the next 5 years. And viscosity grades are getting thinner – there are vehicles on the road that require 0W-16, which is the thinnest oil required currently. In the future, oils may go thinner than 0W-16 as engine design continues to evolve and improve.
If you are wondering what the correct grade of oil is to use for your vehicle, look in your vehicle owner’s manual. Another great source to find the correct oil for your vehicle is the Castrol Oil Selector.