For car enthusiasts, watching a beloved vehicle age can be heartbreaking. The engine no longer roars with the same vigor, and performance begins to decline. But there’s hope—zinc replacement additives might be the solution to breathe new life into an aging engine and restore its former glory.

Owning a classic car isn’t just about transportation—it’s about preserving a piece of automotive history. Whether it’s the unique driving experience or the timeless aesthetic, these vehicles deserve meticulous care. For classic and modified cars, choosing the right maintenance products is crucial, and zinc oil additives offer an ideal solution for optimal protection.

The Role of Zinc Additives in Vintage Engines

Zinc additives provide significant benefits for older engines, particularly those with flat-tappet camshafts. Understanding the necessity of wear protection and the specific needs of vintage engines reveals that modern oils often fall short. Standard oils available today may lack the necessary components to safeguard older engines effectively.

Instead of relying on high-zinc oils or modern formulations not designed for classic cars, zinc replacement additives present a smarter alternative. These products deliver the required wear protection without the drawbacks associated with excessive zinc content.

What Is High-Zinc Oil?

High-zinc oil is an engine lubricant infused with zinc additives to combat friction-related issues. Many vintage car owners opt for high-zinc oil to mitigate the additional stress caused by heat and friction. The elevated zinc levels are particularly beneficial for vehicles subjected to extreme conditions—temperature fluctuations, rough terrain, sustained high-speed driving, or performance demands.

The primary function of zinc-infused oil is to prevent direct metal-to-metal contact between engine components. By forming a protective film, the oil ensures smoother operation. Due to its superior performance, high-zinc oil is commonly used in high-performance racing and off-road vehicles. It’s also an excellent choice for vintage cars with flat-tappet camshafts, given their design characteristics.

Why Do Camshafts Need Zinc Oil?

The camshaft is often the primary reason an engine requires zinc or a zinc alternative. This need stems from the camshaft’s critical role in flat-tappet engines.

As the camshaft rotates, its lobes press downward, opening the engine’s valves. The camshaft followers—components that move with the cam—roll or slide along the cam’s surface. At high speeds, the friction between the cam and followers generates immense pressure.

This pressure can force oil out of the contact area, leading to insufficient lubrication and potential damage. To prevent this, anti-wear additives are essential. For older vehicles with flat-tappet camshafts (as opposed to modern roller cams), the oil must contain zinc or a suitable substitute.

Zinc additives bond with engine metals, forming a protective layer that withstands high pressure and ensures smooth operation. In short, flat-tappet engines need zinc or a replacement additive to prevent premature wear on lifters and camshafts.

How Do Zinc Additives Work?

The "zinc" in oil typically refers to zinc dialkyldithiophosphate (ZDDP), a compound that serves as an anti-wear agent. Sometimes, it may also include zinc dithiophosphate (ZDTP), a phosphorus-based component that enhances protection. For simplicity, industry professionals often refer to ZDDP as "zinc."

ZDDP and ZDTP have long been used in oil formulations to minimize wear. When combined, zinc and phosphorus provide superior protection, making them ideal for high-stress applications.

Zinc additives activate under heat, shielding high-friction areas. As temperatures rise and metal surfaces come into close contact, ZDDP decomposes, triggering a chemical reaction that protects engine components from damage.

When engine parts move, mechanical interactions occur within or on the surface of the ZDDP anti-wear film. This film reduces metal-to-metal contact, minimizing wear. For high-performance engines or those with flat-tappet camshafts, zinc-infused oil is indispensable.

Oil testing on vintage engines has shown that during the initial warm-up phase, lubrication demands exceed what modern zinc-free oils can provide. Without sufficient protection, metal surfaces may suffer damage. Suitable oils for these engines often include higher ZDDP/ZDTP concentrations.

How Do Zinc Additives Affect Vintage Engines?

If an older vehicle has a flat-tappet lifter engine, zinc or a zinc substitute is essential. Adding zinc to the oil prevents premature wear on lifters and camshafts. Most V6 and V8 engines produced before 1988 were designed to use zinc-enhanced oil.

Engines manufactured before the 1980s predominantly featured flat-tappet camshafts, which generate significant friction. Later roller-cam designs reduced this friction, but classic cars with flat-tappet setups still require zinc additives.

Without protection, friction can cause extensive damage. Heat from friction may harm engine components, while wear on the camshaft can degrade performance and efficiency.

Although many oils once contained zinc, modern formulations often exclude ZDDP and ZDTP. Today, most standard oils are zinc-free, making them unsuitable for classic engines. Some manufacturers still produce zinc additives or alternatives, but careful selection is crucial.

ZDDP and ZDTP levels are measured in parts per million (ppm). For zinc oil, the ideal ZDDP range is 1,000–1,400 ppm, with phosphorus levels in a similar range.

Potential Drawbacks of Zinc Additives

If zinc is so beneficial, why has the industry moved away from it? Research has shown that zinc can harm engines. Small amounts of oil enter the combustion chamber, where zinc turns to ash and exits through the exhaust system.

This ash can accumulate on the catalytic converter, reducing its efficiency over time. Left unchecked, zinc-related damage may necessitate costly repairs. Additionally, phosphorus in zinc additives can lead to carbon buildup in valve trains or cylinder bores.

To address these issues, most modern oils have drastically reduced zinc content. Boron has been introduced as a substitute, but it doesn’t match zinc’s protective qualities. The shift to zinc-free oils has also compromised cold-start protection for older engines.

Due to these concerns, many oil manufacturers avoid zinc entirely to protect catalytic converters in modern engines. However, vintage vehicles still need robust anti-wear protection, making zinc or its alternatives necessary.

Why Choose Zinc Replacement Additives?

Zinc replacement additives provide comparable lubrication and protection without ZDDP’s negative effects. Zinc can damage catalytic converters, increase emissions, and shorten component lifespans. In response, OEM manufacturers and the EPA have mandated reduced ZDDP levels in oils.

While these regulations protect newer vehicles, they leave classic engines in a bind. These engines need zinc for wear protection but must also comply with environmental standards. Zinc replacement additives offer a solution—delivering the same high-level protection without zinc or phosphorus.

Advantages of Zinc Replacement Additives

For vintage cars, zinc replacement additives offer several key benefits:

• Superior Protection: These additives outperform ZDDP-based oils without harmful side effects.
• No Engine Damage: Unlike zinc oils, replacements don’t harm catalytic converters or emission systems.
• Environmental Responsibility: By eliminating heavy metals, these additives reduce harmful emissions.
• Cold-Start Protection: They minimize wear during cold starts, a critical concern for infrequently used vehicles.

When Should You Use Zinc Additives?

Experts recommend higher zinc levels during an engine’s break-in period, when uneven wear poses the greatest risk. Zinc replacement products can provide equivalent protection without excessive zinc.

Even after break-in, zinc additives help reduce long-term wear. They ensure smooth operation, minimizing friction and heat. For flat-tappet cam engines, specialized oil with zinc or a substitute is always necessary.

Flat-Tappet vs. Roller Cams

Determining whether to use zinc additives depends on engine type. Flat-tappet cams require zinc, while roller cams do not.

Flat-tappet designs are prone to wear due to sliding contact between the cam and lifters. Without proper lubrication, friction can damage valve operation, reducing engine efficiency and power.

Roller cams, on the other hand, use rolling contact, drastically reducing friction. Since zinc isn’t needed—and may even cause harm—roller-cam engines should avoid high-zinc oils.

For maximum longevity, flat-tappet engines should always use zinc or a replacement additive, whether during break-in or routine maintenance.