A Guide to Motor Oil Additives

Oil changing is an important car maintenance task, and different motor oils you can buy in the market have various additives. It's advisable to choose the one that is appropriate for the type of engine in your car by consulting the manufacturer’s instruction manual. Using the wrong oil can cause damage to your engine and you could void the warranty on it by doing so. The best guide to making the right choice is the American Petroleum Institute Certified (API) Starburst stamp. The API donut also helps you by indicating the performance of the motor oil, and its viscosity at different temperature levels or in other words, the Society of Automotive Engineers (SAE) rating. You also learn whether it helps you conserve fuel.

Understanding viscosity

When choosing motor oil for your car, the most important consideration to keep in mind is its viscosity or thickness. Motor oils that are too thick will not flow freely and cannot move through all the moving parts of your engine. They cannot effectively protect your engine from friction, contaminants and overheating. However, if the motor oil is too thin, it will not be able to coat the engine properly and is also ineffective.

Ambient temperatures can also affect the thickness and fluidity. Motor oils tend to thicken at lower temperatures and thin when the temperature rises. As a result, starting up the engine in winter can be more difficult and also consumes more fuel to reach the optimum temperature for combustion. Accordingly, manufacturers include additives in the motor oil so that it remains stable and continues to perform well. The figure you see on the API donut indicates the viscosity of the motor oil in winter and also, its fluidity after warming up sufficiently. The different additives have various properties, each contributing to the efficient working and life of your car engine.

Types of motor oils

  • Conventional motor oils: If you have just bought a new model car and intend to use it for commuting short distances and light duty, where the engine is not likely to heat up excessively, then conventional motor oil like Castrol GTX will work very well in it. These oils have chemical additives and are available in a range of viscosity levels. If you’re using conventional oils, you’ll need to change the oil and filter in your car every 4 months or 4000 miles. Many of the latest model cars also have an electronic oil-change indicator on the dashboard to alert you.

  • Synthetic motor oils: Synthetic oils, specifically Castrol EDGE, undergo strict quality control tests and are effective at both hot and cold temperatures. They do not evaporate easily, have a better viscosity range, and protect the engine against contaminants and overheating. Castrol synthetic oils have a higher than usual percentage of additives and are considered high-quality motor oils. Most car manufacturers recommend that you use them.

  • Synthetic blend motor oils: Synthetic blend oils include a combination of synthetic and organic oils. They are specially designed to protect your engine from oxidation, overheating and are ideal for use in heavy-duty vehicles that frequently carry loads, operate on uneven terrain, and tow trailers. These oils also help with fuel conservation.

  • High mileage oils: High mileage oils including Castrol GTX High Mileage are designed for older vehicles that have seen long mileage or usage. These oils include additives that maintain its viscosity better and protect the engine from wear. They typically have a high viscosity and seal conditioners to help protect the bearing seals. In this way, they work to prevent oil leaks and restore the compression in the engine combustion chamber. Cars with older engines perform better with Castrol GTX High Mileage.

Additives in motor oils

Motor oil typically contains a Performance Additive Package that can make up 15% to 25% of its composition. The remaining percentage is base oil. The additives help to enhance the performance and viscosity of the motor oil. Oil manufacturers design their products to comply with the specifications of car companies and engine manufacturers.

  • Viscosity-index additives: The Viscosity Index indicates the capacity of the motor oil to remain stable despite temperature fluctuations. The polymer additives ensure that the motor oil maintains its viscosity over a diverse range of temperatures.

  • Dispersants: These additives absorb and hold solid contaminants within the oil so that they do not damage the engine. In this way, they delay the forming of sludge, acids and varnish.

  • Detergents: These additives act on the piston-ring area, piston under-crown and other surfaces that overheat. They prevent the forming of deposits, rust and corrosion; and are used up over time.

  • Anti-wear agents: Anti-wear agents work 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.

  • ZDDP: ZDDP (zinc diakyl-dithiophosphate) is a zinc and phosphorus compound that until recently, formed a component of anti-wear additives. However, because of its propensity to damage the catalyst in converters, fewer oils now contain it. Even so, older vehicles that have a flat-tappet camshaft or an altered engine with higher-than-stock spring pressures need special motor oils that include this compound. The ZDDP provides the necessary lubrication to the cam lobes, lifter bodies, lifter bores and other engine parts.

  • Friction modifiers: Graphite or molybdenum is a friction modifier that helps lower friction when the engine is operating under high temperatures and heavy loads. These additives also help you conserve fuel. They lose their effectiveness over the life of the motor oil.

  • Antioxidants: 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.

  • Anti-foam additives: If the motor oil foams and forms bubbles, it is unable to coat all the important parts of the engine and keep it cool. As a result, it can cause serious damage to your engine, especially under high temperatures. Anti-foam additives prevent air from getting compressed in the oil and the forming of foam even if there is an excess of oil in the crankshaft because of accidental overfilling. In case of engines that have variable camshaft timing, the motor oil must also act as hydraulic fluid. Aerated motor oil will be unable to provide this function.

  • Rust and corrosion inhibitors: 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.

  • Pour-point depressants: 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.

  • Dexos: Dexos engine oil is specially formulated engine oil created by General Motors engineers. It is used specifically in GM engines and works to provide a better mileage, reduce emissions and prolong the life of the emissions system. It has better anti-foaming additives and needs changing less frequently as compared to other motor oils. The dexos motor oil has better abilities to prevent the buildup of sludge and also helps protect the catalytic converter from damage. The biggest advantage of dexos is that you can use it in your car at the next oil change even if you have used other oils previously.


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