Choosing the right oil for your vehicle is more complicated than you would think. BIZOL wants to give you the facts and point out what to look for when buying an oil. We want to give you the right answer, not the simplest answer.

Over the course of a few articles, we will attempt to break down the complexities of oil and why motor vehicles need it. We will also try to bust a few myths that have arisen and spread over the years. We will show you that technology has moved on and that many of the things that once might have been true simply no longer apply.

It was our intention to make the guide as easy to read as possible but without omitting interesting and vital information and we hope we have succeeded. We also hope that you enjoy our brief excursion into the science and de-bunking of some of the myths about oil. If you enjoy our offering, please spread the word by letting others know about it, also feel free to like the post and share it on facebook.

So, let’s get down to the basics.

What is engine oil, what tasks does it actually perform and how does it work?

Lubrication is the single most important function an oil has to perform, regardless of any other functions. Assemblies with moving parts need a lubricant to minimise friction and stop the sliding surfaces seizing or welding together due to a build-up of heat.

The need to keep friction low is critical and is even necessary in components which are made from ‘self-lubricating’ materials, such as cast iron. Lubrication works, for example, by trapping oil in irregularities, scratches, etc of the lubricated surface. To ensure the cylinder walls in an engine stay lubricated, the oil is held on the cylinder wall by a criss-cross pattern that is machined into the surface of the cylinder wall. The criss-cross pattern literally traps oil, preventing it from running down the cylinder wall and leaving the surface dry and unprotected. Honing, is the machining process that creates the criss-cross pattern on the cylinder walls.

Figure 1 – Honed cylinder liner

Figure 1 – Honed cylinder liner

Five functions

If we look at the internal combustion engines (ICE), it is clear to see that it is a highly complex machine. And the fact that engines are complex is the reason why oils have to be able to cater to all of the needs of an engine, not just its lubrication needs.

Figure 2 – Five functions of oil
Figure 2 – Five functions of oil

The five main functions of oil:

Lubrication — Oil provides a fluid film to prevent metal-to-metal contact, allowing moving parts to slide smoothly, reducing friction, wear and fuel consumption.
Sealing — Oil actively seals small gaps between components such as the pistons rings to prevent the escape of gases.
Cooling — Oil absorbs heat when travelling around the engine and transports it away from the hot components.
Cleaning — Detergents and dispersants contained in the oil clean away dirt and deposits from components and transports them away.
Protection — Rust inhibitors contained in the oil prevent the formation of rust and protects surfaces by creating a fluid film to lower friction.

Lubricant selection

All oils have to perform the five functions regardless of any other requirements. The latest generation of engines put even greater demands on the oil used in terms of protection and cleaning.

Engine oils are blended from a combination of base oils and additives. So, when it comes to selecting a suitable lubricant, the application and specific requirements must be identified and considered first. Regardless of conventional wisdom, the suitability of an oil boils down to the finished oil’s characteristics and whether it meets certain specifications; the base oil used is just one factor in such calculations.


Lubricant manufacturers co‑operate with vehicle manufacturers to find the best combination for each application. Specific targets are set for what the lubricant has to achieve in terms of fuel economy, corrosion protection, turbocharger protection, soot emissions, etc. Only when tests have been completed and designated targets have been met is the lubricant manufacturer allowed to claim that its oil meets a specific industry standard or is awarded an approval by a motor manufacturer.

This is why it is so important that an oil has a manufacturer’s approval and fulfils standards such ACEA and API standards. Meeting industry standards and attaining manufacturer’s approvals is a genuine indicator of an oil’s quality, because only approved oils are adjudged by the motor manufacturer to be good enough.

Figure 3 – Spiderweb diagram A5/B5 ACEA specification

The spiderweb diagram in figure 3 shows what an ACEA A5/B5 designated oil has to achieve in terms fuel economy, wear, deposits, etc. All oils bearing, for example, the A5/B5 designation must fulfil the requirements represented in the diagram shown in figure 3. The rules apply to all oils and there is a regulatory framework for each standard and each body i.e., the API, JASO, ACEA or ILSAC sets their own standards. Lubricant manufacturers have to submit their oils to tests in order to attain these accreditations, so that the customer can be sure that they know what they are buying.

When selecting an oil, make sure that it meets the industry standards and is right for your application.

2 replies
    • Bizol-Team
      Bizol-Team says:

      Hi SAM,

      thanks for your comment. We are trying to give our customers an insight into some of the facts behind the claims and give people a chance to understand why we say, what we say. Please enjoy the rest of the rest of the ‘Explainer’ series and spread the word. BIZOL wishes happy motoring.


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