Zinc Additive For Engine Oil: How Much To Add (And Do You Even Need To?)

As someone who's driven classic cars daily for around 15 years, as well as working on and restoring such cars throughout my education, I take vintage automotive maintenance very seriously. Many of these vehicles require specialized care and certain products due to their age, mileage, and general usage history. That's why some oil companies produce "high-mileage" and similar blends –- perfect, for instance, in cars like my classic Jeep or Volkswagen. Typically, these oil blends feature a number of additives one can purchase separately, with a major component being ZDDP, more commonly referred to simply as zinc.

The amount of zinc your classic car needs depends on its age and apparent wear, with around 1,000 to 1,200 ppm sufficient for most applications (less if you have catalytic converters, as zinc causes buildup in a catalytic converter's elements). For instance, my Jeep has about 200,000 miles and a catalytic converter, so I use 1,000 ppm in my older straight-six. My Volkswagen, however, needs more like 1,200 ppm in the air-cooled 1600 with about 100,000 miles and no catalytic converter.

Does your car need zinc additive, though? Well, all oils you buy off-the-shelf come pre-mixed with additives such as zinc (usually 800 ppm), which are designed for modern engines because these represent the vast majority of cars on the road today. So, realistically, if you own a regular low-mileage modern car (anything made after the 1980s), zinc additives are not strictly necessary. However, if you own a vehicle made during or before the 1980s or one with a vintage-style, high-mileage, or high-performance engine, you should consider adding zinc the next time you change your oil to help protect the working surfaces from wear. Further, you should change the oil more often to help maintain this effect in such engines.

Zinc dialkyl dithiophosphate (ZDDP), or just zinc, acts as a protective film across working surfaces, enhancing the engine oil's properties by providing a barrier between metal components. Think of zinc as the cartilage in your knee. Within the engine, zinc prevents metal-on-metal contact, which could result in premature wear and damage. It's particularly useful in high-performance applications as well because the higher pressures involved in such engines might not be sufficient for some engine oil to handle. Adding zinc allows such oils to better withstand those higher pressures and maintain a consistent coating.

This is especially important in older engine designs, specifically ones with flat-tappet cam lobes. That's because of how these lobes work; compared to a roller-tappet cam profile, older flat-tappet cams exert higher pressure on the working surfaces. In other words, you're spinning a flat surface against the valvetrain, which requires more work to achieve than a rounded surface. Zinc helps prevent friction-based wear of these critical valvetrain-related components, as well as the cam lobes, by providing a smooth, slippery buffer between the two surfaces. It also helps prevent excessive heat buildup in working components subjected to high temperatures, such as pistons. However, too much zinc additive could potentially result in a buildup inside the combustion chamber, so only add as much as needed.

Again, these factors largely only apply to classic, high-performance, or very high-mileage engines. For the average modern car, typically, whatever the manufacturer recommends in the user manual will suffice in terms of engine oil, with high-mileage blends useful for when your car reaches six-figure digits.