The role of additives in motor oil performance

[wemay]

The role of additives in motor oil performance | Africa Automotive News

africaautomotivenews.com

Quotes from various oil manufacturers including below...

"...Oliver Kuhn, Deputy Head of the Oil Laboratory at LIQUI MOLY GmbH, says, “Additives deliver the performance of the motor oil. Motor oil consists of two main components: base oil (the actual oil) and the additive composition. In the latest motor oils, the role of the base oil is more or less reduced to a carrier fluid for the additives. Even lubrication is provided rather by the additives than by the base oil.” Liqui Moly GmbH is a German company specializing in oils, lubricants and additives..."

 

[RDY4WAR]

For the most part, that is true. The rod and main bearings are the only part of the engine that operates solely in full hydrodynamic lubrication. Every other part of the engine sees mixed or boundary lubrication.

 

[SteveG4]

I particularly liked the spelled-out roles of additives at the end of the article:

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The specific role of additives​

• Oxidation inhibitors. (antioxidants), Oxidation is the general attack of the weakest components of the base oil by oxygen in the air. It occurs at all temperatures all time but accelerates at higher temperatures due to presence of water, wear metals and other contaminants. under conditions of high temperatures in the engine, the motor oil can oxidize when reacting with oxygen. If that happens, the motor oil ages quickly, thickens and forms sludge. Antioxidants work to slow down this oxidation and the forming of deposits. They also help to keep the engine clean and prolong the life of the motor oil.
• Rust and corrosion inhibitors. These additives reduce or eliminate internal rust and corrosion by neutralizing acids and forming a chemical protective barrier to repel moisture from metal surfaces to protect lubricated surfaces against rusting and corrosion. The internal parts of the engine can rust and corrode because of exposure to moisture and acids. These additives create a film over the parts and protect them against damage from these hazards.
• Anti-wear agents and/ or extreme pressure (EP) agents. These additives are typically used to protect machine parts from wear and loss of metal during boundary lubrication conditions. They are polar additives that attach to frictional metal surfaces. They react chemically with the metal surfaces when metal conditions of mixed and boundary lubrication to protect parts of the engine that are susceptible to high temperatures such as cylinder walls, piston rings, lifters and cams. These additives form a protective layer on these components and prevent the friction that can occur because of metal-to-metal contact. They also act as antioxidants and are used up over time. They also help protect the base oil from oxidation and the metal from damage by corrosive acids
• Demulsifiers to promote oil-water separation.
• Viscosity Index (VI) Improvers are very large polymer additives that partially prevent the oil from thinning out (losing viscosity) as the temperature increases. The long-chain polymers help control the viscosity of multi-grade motor oils. They expand and contract as temperatures vary. High temperatures cause VI improvers to expand and reduce oil thinning; low temperatures cause VI improvers to contract and have little impact on oil viscosity. They are also responsible for better oil flow at low temperatures, resulting in reduction in wear and improved fuel economy.
• Pour-point depressants to lower the cold temperature fluidity of petroleum products. These additives work to prevent the hardening of wax particles in the motor oil under cold conditions. As a result, the motor oil flows freely even at low temperatures and does not need the engine to work harder to pump it. In this way, the engine continues to function effectively despite fluctuations in the outside temperature.
• Detergents and dispersants. Detergents perform two functions, they help
  (clean) and neutralize acids that form in the oil. Detergents are primarily used in engine oils and are alkaline or basic in nature to keep hot metal components free of deposits and to maintain cleanliness of lubricated parts by taking care of the soot present in the lubricant. They are typically materials of calcium and magnesium chemistry. A detergent additive is normally used in conjunction with a dispersant additive. Dispersants are mainly found in engine oil with detergents to help keep engines clean and free of deposits. The combination of detergent/dispersant additives allows more acid compounds to be neutralized and more contaminant particles to stay suspended
• Anti-foam agents. The chemicals in this additive group possess low interfacial tension, which weakens the oil bubble wall and allows the foam bubbles to burst more readily. They have an indirect effect on oxidation by reducing the amount of oil air contact to reduce foaming tendencies. If the motor oil foams and forms bubbles, it is unable to coat all the important parts of the engine and keep it cool.
• Tackiness agents. These additives increase the adhesive properties of a lubricant, improve retention, and prevent dripping or spattering.
• Friction modifier. This additives alter coefficient of friction, and can be used to give oil more ‘slippery’ characteristics. In motor oils, friction modifiers are used to increase the oil’s lubricity for the purpose of reducing friction and improving fuel economy.

Have a great day!

 

[ZeeOSix]

For the most part, that is true. The rod and main bearings are the only part of the engine that operates solely in full hydrodynamic lubrication. Every other part of the engine sees mixed or boundary lubrication.

Cam shafts (and balancer shafts if used) also run in journal bearings.

 

[bonjo]

I am not sure about the comment regarding the base oil. I am of the opinion that synthetic base oil is far superior to mineral one and also that the additive requirement is not as much.

Back in 1985 when I switched to mobil FS, the perfomance difference was amazing compared to mineral oil and I don't think it had much additives in it in those days