Lubricant Additives

Why are Viscosity Modifiers so Important?

Viscosity Index Modifiers are crucial to a lubricants performance, helping to protect the key moving parts of your vehicle

In recent months, one of the hottest topics in relation to lubricants has been additives, specifically Viscosity Index Modifiers. They perform an integral function within all lubricants and are readily available in automotive resellers. But before you go out and buy them, it’s essential that you understand their role and the benefits they bring. If we look at this through an engine oil, we can highlight just how important this formulation is.

Engine oil has several key functions to perform to ensure that your vehicle operates at an optimum level.

  • They reduce friction between the moving parts of your engine
  • Protect metallic surfaces from corrosion.
  • They remove impurities and clean existing deposits and foreign substances in the engine
  • Act as a sealed space between the piston and cylinder
  • Cool the upper engine and its parts.

It is extremely rare that an engine oil can perform all these tasks alone. Extra chemical compounds or additives are formulated with the oil to help with these functions without the addition of extra chemicals. The most important of these engine oil additives are viscosity index modifiers.

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What is the Viscosity index?

The viscosity of a lubricant is essentially its resistance to flow. It is the most important consideration of the oil as it affects both the wear and tear rate of the engine and its readiness to flow freely through the engine and coat all the parts that need coating.

Oil with too high a viscosity will be reluctant to flow while on the opposite end of the spectrum, oil with too low a viscosity can shear easily, and the molecules move quicker.

In both instances, this can cause metal to metal contact as the engine operates. Temperature also has a direct impact on the viscosity of engine oil. Higher temperatures will make the oil thin while lower temperatures will do the opposite.

This tendency to change is called its viscosity index. Viscosity index is the measure of the change in viscosity due to the effects of temperature variations.

Engine Oil Viscosity

What are Viscosity index Modifiers?

Viscosity Index Modifiers (aka Viscosity Index Improvers) are additives that are sensitive to temperature. They are made up of polymeric molecules that form “chains”. At lower temperatures, the molecule chains contract and have no real impact on the viscosity. However, at higher temperatures, the chain relaxes and expands, increasing the viscosity.

Viscosity Modifiers

 What does this mean for your oil? An oil with a low viscosity is needed to protect an engine at low temperatures so the oil can be pushed through the moving parts quickly.

The oil must also be viscous enough to protect the engine as it reaches operating temperatures.

The viscosity modifiers ensure that your vehicle is protected efficiently on a winters morning or whilst driven at engine temperatures well in excess of 90 °C.

The majority of modern engine oils on the market today have viscosity index improvers.


What Are Other Common Additive Types?

Two of the most common types of engine oil additives are corrosion inhibitors and detergents/dispersants. Corrosion inhibitors are additives that neutralise acids and form a chemicals protective barrier to repel moisture form metal surfaces.

Detergents help remove sludge that can build up in the engine over a length of time while the dispersants will keep the dirt from coming together. Zinc is also added to many engine oils as it helps to protect engine surfaces.

Most of these “additives” will already be in the oil as it comes from the manufacturer, so they do not have to be added by the car owner. But if you walk into any number of automotive stores, you can find numerous bottles of aftermarket engine oil additives that will state that they will improve performance even further and clean your engine better than the detergents that are already in your oil.

It is extremely important to remember that the oil you are buying has been created to perform specific functions and that the additives are balanced to perform these tasks. Adding excess additives will affect this balance detrimentally lowering performance. Always follow the instructions in your manufacturer’s manual.

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Other Oil Additives to Watch Out For

As we have seen there are a number of additives available but what is considered the most important to watch out for?

  • Viscosity modifiers are extremely important additives. Oil stabilisers can also be counted in this bracket as they both help the oil last longer.
  • Anti-wear additives that are used to prevent metal to metal contact, commonly made from zinc compounds.

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Finol provides the go-to app in choosing your engine oil, Which Oil. This leading lubricant advisor is extremely easy to use.  Go to, choose your vehicle and fill in your details. Within seconds you will be brought to the most suitable lubricants for your vehicle.  For further information, go to or contact our dedicated technical team at 01-455 5484

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