Getting the Basics Right: Base Oils
Lubrication has been around since the invention of the wheel. Horse-drawn carts with wooden axles used meat greases, pine tar and various forms of animal fat as lubricants. Later, Linseed oil, originally a wood preserver, briefly replaced them as the primary lubrication agent.
The earliest internal combustion engines used a product derived from refined crude oil. This was the beginning of the modern base oil. As IC engines became more complex and operated at higher speeds and temperatures, there was a need for better lubrication that could keep up with modern engines. So, additives were supplemented with the base oils. This combination had improved viscosity and protected the engines from wear, friction and resisted corrosion better.
In modern cars, the base oil is still the primary catalyst for better engine performance. It forms 75%-80% of the finished product while the additives (10%-20%) and the viscosity index improver, which keeps the viscosity within a threshold at higher temperatures, make up the rest of the engine oil composition along with a variety of inhibitors.
We currently produce base oil by refining crude oil. Less than 1% of the standard 42-gallon barrel of crude oil is used to make lubricants—while the rest becomes gasoline, diesel and kerosene-type jet fuels.
The American Petroleum Institute classifies base oils into five groups (I-V) based on how they are processed. Group I and II are called mineral conventional base oils. Generally, Group II oils are more refined than Group I. They have higher purity levels and lower amounts of Sulphur, nitrogen, and aromatics. They also have superior oxidation stability. The best Group II oils are clear as water—it is only the additives that give the oil its dark color. Group I oils have mostly gone out of use because Group II oils are an effective substitute wherever the former is needed.
Group III and IV base oils are of relatively higher quality. They are used to produce high performance, low viscosity grade (0W-20) engine oils for advanced and demanding engines. Engine oils produced from these two groups are classified as synthetics because they have superior oxidation properties, improve fuel economy, and last longer. There is still some discrepancy to what classifies as truly synthetic because in some parts of the world, only Group IV, also called poly-alpha olefins (PAOs), are considered synthetic.
Choosing what group to use depends on various factors. Primarily, the application and operating conditions like temperature (extreme hot and cold), the required drain intervals, performance levels, and even traffic conditions dictate which base oil should be used.
Base oils have four physical properties that decide how they will perform:
- Pour point—the lowest temperature at which the oil can be poured
- Viscosity—the internal resistive property of the oil that determines how it flows
- Viscosity index (VI)—the change is viscosity in relation to the temperature. Oils with a high index number change less when the temperature increases or decreases than oils with low VI. Generally, multi-grade engine oils that have lower volatility and operate at extreme temperatures, require high VI base oils in their formulation.
- Purity—the amount of Sulphur, nitrogen and polycyclic aromatics. Pure base oils have lower levels of these compounds
In summary, base oils form a large part of the final product. Choosing the correct base oil is crucial in producing engine oils that will keep all parts of the engine lubricated and improve its performance. But base oils are only the part of the story. Lubricant makers must also consider the impact of additives because the engine performance is dependent on how the combination of base oils and additives work together.