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Oil Additives: What’s In My Engine Oil?

Beakers with different liquids. Oil additives make up a large part of engine oil. Wrapping your head around the different types of additives in oil can be a daunting task. Here's a quick guide to getting a better understanding of what's in your oil.

Looking at a typical bottle or jug of engine oil, it might come as a surprise that 10 to 30% of that jug is something other than oil. Before looking for a replacement for your next oil change be assured those 10 to 30% oil additives are better for the engine than oil alone. The same holds true for the oil additives in gear oil and transmission oil. These additives enhance beneficial properties, suppress undesirable properties and add new properties to the base oils.

Oil alone is a good lubricant and anti-corrosive, but in a hot engine or high-torque gears, it can overheat, foam up or squeeze out. Any of these situations is bad news for the components it’s supposed to protect. Up to 30% of engine oil is oil additives like viscosity improvers, anti-oxidants, corrosion inhibitors, detergents, dispersants, anti-wear, anti-foam and alkalinity improvers. Gear oils are typically up to 10% anti-oxidants, anti-wear, anti-foam, corrosion inhibitors and extreme pressure anti-shear additives.

Common Engine Oil Additives

  • Viscosity improvers help engine oil flow better in cold weather. A 5W-20 oil blend, for example, flows like 5-weight oil at 0-degrees Fahrenheit, but no thinner than 20-weight oil at 212-degrees Fahrenheit. This makes for easier cold-weather starting without sacrificing normal-operating-temperature protection.
  • Detergents/dispersants are polar molecules that bond to particles in suspension in the oil, such as soot particles or metal flakes. This prevents them from clumping together and sticking to metal surfaces, eventually flowing to the oil filter where they are strained out.
  • Anti-wear additives, such as zinc dialkyl dithiophosphate (ZDDP) and molybdenum disulfide (moly), bond with metal surfaces to create a chemical load-bearing coating. Instead of wearing the metal, the additives shear, preventing true, metal-to-metal contact and reducing wear.

Engine Oil Additives Help Oil Protect Your Engine Even BetterFor most applications, stock oil blends include everything needed for performance and protection of the intended engine, gearbox or differential gears. One might consider additional additives for high-performance engines, extreme-performance differentials or high-mileage engines. A heavy-duty oil stabilizer can be useful in heavy-duty and high-wear applications. Certain limited-slip differentials (LSD) may require a specific oil additive to maintain the LSD clutches.

How Engine Oil Wears Out

Interestingly, the oil itself is practically indestructible, oxidizing only in high-heat situations. On its own, base oils would lubricate and protect the engine for a couple of thousand miles, maybe less. Oil additives significantly improve the effectiveness of base oils in all kinds of engines and gearboxes, in some engines upwards of 15,000 miles. Eventually, these sacrificial additives burn off, evaporate or wear out.

When oil is worn out, the additives are used up, leaving the mediocre protection of base oils. At that point, it’s time for an oil change. One might opt for oil analysis to determine the state of the oil at any given time, but the best way to make sure the oil is operating at full capacity is to change your oil on time, every time, with quality oil.

Check out all the lubrication equipment available on NAPA Online or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on the additives in engine oil, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Pixabay.

Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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