Engine Oil Fundamentals – Part 1: Back to basics with Base Oils in engines

To understand lubricating oils, you need to understand their two fundamental components –base oils and additives. Join us in the first part of a three-part introductory primer on engine lubricants, as we take a closer look at their base oil component – the different base oil types, their manufacturing processes, and their impact on the final lubricant properties.


Engines drive activity. To keep this “heart” of activity running smoothly and efficiently, the engine requires the right lubrication and protection, under various and all types of conditions. Lubricants have five main functions:

  • Lubricate moving parts to reduce friction and prevent wear
  • Help clean the engine or machine of contaminants, by reducing the build-up of sludge and keeping particles in suspension
  • Seal piston and cylinder for optimum operating efficiency
  • Cool high temperature areas of engine and machinery
  • Protect metal parts against rust and corrosion

Regardless if you’re a seasoned pro in the industry or a new aspiring talent, below is a quick refresher on the basics of base oils – their different types, manufacturing processes – to help explain their importance in determining the final lubricant properties.

Key Lubricant Performance Characteristics

Engine oils are slightly different from the broader category of industrial oils due to their characteristics. Here’s a quick table to break them down:

Engine Oils

Industrial Oils

Oxidative stability

Oxidative stability

Low temperature rheology


Protection against wear

Protection against wear

Protection against corrosion

Inhibition against rust


Water separability

Reduce deposit formation




What is a Lubricating Oil?

base oil + additive = Engine oilOil barrel

Engine/lubricating oils are made of selected base oils combined with performance-enhancing additives.

  • Additives improve the original properties of the base oil
  • Additives impart enhanced performance characteristics to the base oil
  • Additives help extend the life of the oil

In today’s lubricant landscape, the base oil / basestocks used in engine oils are usually divided into two general categories – mineral or synthetic.

Mineral base oils are distilled from crude oil in a conventional refinery, resulting in oil molecules of non-uniform sizes.

Image of sports balls

Synthetic base oils, on the other hand, are chemically engineered from pure petroleum gases in a chemical plant, or converted from crude oil via severe catalytic hydroprocessing.

Image of soccer balls

These two base oils are subsequently divided into 4 major classifications below. Base oil composition has a significant effect on the overall performance of engine oil. A blend of base oil types is often used to balance performance vs costs.


·       API Group I


Mineral oil

·       API Group II


Highly refined mineral oil

·       API Group III

Severely Hydroprocessed

Very highly refined mineral oil (commonly referred to as Synthetic)

·       API Group IV

PAO Synthetics

Chemically built, i.e. synthesized

PAO = PolyAlphaOlefin


Composition Differences between Basestocks



Group I

Group II

Group III

Group IV

Sulfur (ppm)

2,000 – 7,000

10 – 300

< 10.0


Nitrogen (ppm)


1 – 5

< 1.0


Aromatics (wt%)

15 – 30

1 – 10

< 1.0


Viscosity Index

95 min.

95 – 119

120 – 130

120 – 200+



How Basestocks are Manufactured

Infographic about basestocks

Properties of a PAO in an Engine Oil



What this means?



High viscosity index (VI)

Requires less VI improver, thus less deposits

Reduces ring stick and bore polish

Engine oil is more likely to stay in grade

Good volatility

Lower oil consumption and emissions

Lower fire hazard

Engine oil is more likely to stay in grade

Low pour point

Better low temperature fluidity (pour point -57⁰C)

Better starting performance, which reduces wear

Oxidation stability

Longer drain intervals

Lower levels of sludge, deposit, and varnish



High cost

Costs approx. 4 times more than mineral base oils

Poor solvency

Additives need to be specially selected

Seal compatibility

Oil is prone to attack seal materials

Overall, synthetic lubricants typically provide more robust performance, especially in terms of low temperature pumpability. high temperature stability, and protection against deposits. These attributes can help towards reduced engine wear, fuel economy potential and long engine life.

Synthetic lubricants can also significantly improve fuel economy, working much more quickly than mineral engine oils, so the engine reaches peak operating efficiency that much sooner.

Especially in this day and age, importantly, another advantage of synthetics is that they’re cleaner and environmentally friendlier – helping to cut engine emissions when compared to conventional mineral engine oils. Conventional mineral engine oils also contain greater amounts of impurities, such as sulfur, reactive and unstable hydrocarbons, and other undesirable contaminants that cannot be completely removed by conventional refining of crude oil.

To maximize the benefits of the engine oil and minimize any issues, we strongly recommend businesses to speak with their lube distributor and expert to evaluate and identify the best engine oil most appropriate for their use, as well as the optimum practices to extend its longevity.

In the second part of our primer on engine oils, we’ll talk about what are the different types of additives, why they’re important, and why we need to balance the amount of additives in lubricant formulation.

Do you have any questions about the role of base oils in engine oil? Share them with us in the comments below, or hit “Like” on the toolbar on the right if you found this refresher useful!