Understanding Motor Oil Types, Additives, and Their Functions
Oils & Additives
Types of Motor Oil
- Mineral Oil: Obtained from the distillation of crude oil through various refining processes.
- Semi-Synthetic Oil: A mixture of mineral and synthetic oils, typically composed of 70-80% mineral oil and 20-30% synthetic oil.
- Synthetic Oil: Created through chemical reactions, including esters and synthesized hydrocarbons, specifically polyalphaolefins.
Additives in Motor Oil
Additives constitute approximately 15-25% of motor oil and enhance its properties.
Additives that Improve the Viscosity Index
- Allow the oil to remain fluid enough in cold temperatures to facilitate starting by lowering the freezing point to between -15 and -45°C.
- Maintain sufficient viscosity at high temperatures to prevent contact between moving parts.
- Composition: Polymers that maintain hot viscosity, such as polymethacrylate, copolymers of ethylene, mixed copolymers, isoprene derivatives, and styrene derivatives.
Anti-Wear Additives
- Function: Strengthen the anti-wear action of the lubricant.
- Mode of Action: Form a protective layer on metal surfaces, either directly or through reaction products.
- Composition: Numerous zinc alkyl-dithiophosphates and phosphorus derivatives.
Antioxidant Additives
- Purpose: Eliminate or at least slow down oxidation in the lubricant.
- Content: Dithiophosphates, also used as anti-wear substances, are excellent antioxidants.
Detergent Additives
- Function: Prevent the formation of varnish and deposits on hotter engine parts.
- Mode of Action: Exert a detergent action inside the engine to prevent the buildup of carbonaceous combustion residues.
- Composition: Calcium or magnesium metal salts belonging to alkylaryl-sulfonate, alkylphenate, or alkyl salicylate.
Basicity Additives
- Function: Neutralize acidic waste from fuel combustion, mainly in diesel engines.
- Mode of Action: Neutralize acid residues in the lubricant as they form.
- Content: Phenols, sulfonates, or salicylates are basic neutralizers.
Dispersing Additives
- Function: Keep all solid impurities formed during engine operation suspended.
- Mode of Action: Prevent clumping of solid waste and limit deposit formation in the colder parts of the engine.
- Composition: Polar compounds from the family of alkenyl succinimides.
Anticorrosive Additives
- Function: Prevent corrosion of ferrous metals due to the combined action of water, oxygen, air, and certain combustion oxides.
- Mode of Action: Form a protective coating or passivate the metal surface.
- Composition: Mainly alkaline or alkaline-earth sulfonates, neutral or basic (salts of Na, Mg, Ca).
Antifreeze Additives
- Function: Allow the lubricant to maintain fluidity at low temperatures (-15°C to -45°C).
- Mode of Action: Influence the rate and processes of paraffin crystallization in mineral oil.
- Composition: Products such as methacrylate, copolymers, maleate styrene, naphthalene paraffins, and vinyl acetate-fumarate polyesters.
Anti-Foam Additives
- Cause: Foam can appear in oil due to the presence of detergent additives, which act like soap in water.
- Function: Limit the dispersal of a large volume of air in the oil.
- Composition: Silicone fluids or alkyl acrylates present in small amounts.
Extreme Pressure Additives
- Objective: Reduce friction and thus save energy.
- Mode of Action: Provide specific lubricating and sliding properties, mainly for gears or friction linings.
- Composition: Common families include organometallic derivatives of molybdenum and certain components derived from fatty acids.