Why do we need oil additives?Understanding Engine Oil and how it works


As we have seen from our previous articles, engine oil has a number of key functions to perform. They reduce friction between the moving parts of your engine and protect metallic surfaces from corrosion. They can also remove impurities and clean existing deposits and foreign substances in the engine, act as a sealed space between the piston and cylinder and also help cool the upper engine and its parts. It is extremely rare though that the engine oil can perform all these tasks without some form of help. Extra chemical compounds or additives are added to the oil to help with these functions without the addition of extra chemicals and the most important of these engine oil additives are viscosity index improvers.

The viscosity of a lubricant is fundamentally 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 spectrum oil with too low a viscosity causing the metal to metal contact. 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. Viscosity index improvers are additives that are sensitive to temperature and used to alter this index to make the change in viscosity small enough throughout the car’s normal range of temperatures that the oil will be useful whether your car is just being started on a winter morning or driven at engine temperatures well in excess of 90 degrees. Nearly all modern engine oils have viscosity index improvers.


What are other common additive types?

Two other common types of engine oil additives that you will come across are rust inhibitors and detergents/dispersants, detergents help Engine oil for a carremove 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 manufacturers manual.

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?

  • As we have already read 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.


Finol provides the go-to app in choosing your engine oil. Go to the Finol Which Oil App choose your vehicle and fill in your details. Within seconds you will be brought to the best oil for your vehicle. Our full range of products can be viewed here or you can contact one of our specialised team members by clicking here

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Finol Oils, 3 Stannaway Drive Crumlin Dublin 12 | Tel:+353 01 4555484