Your Guide to High-Zinc Motor Oil

The use of zinc in motor oil is nothing new. In fact, it’s been used to protect vehicle camshafts for years. But what does it do exactly, and is it still a good idea to use high-zinc motor oil in modern engines? Let’s take a look at how this motor oil additive can help or harm your engine.

What Is High-Zinc Motor Oil?

The zinc in motor oil isn’t the plain zinc listed on the periodic table. “Zinc” in motor oil is the shorthand for zinc dialkyl dithiophosphate (ZDDP). The compound has anti-wear properties and bonds easily with metal surfaces, making it the perfect coating for the camshaft and followers because it can withstand the high pressures in these areas. Unfortunately, zinc does have its downsides, which we’ll look at in a later section of this article.

For now, all you need to know is that high-zinc motor oil is simply motor oil with a higher-than-usual concentration of ZDDP and other phosphorus-based additives.

Benefits of Zinc in Motor Oil

The main benefit of zinc in motor oil is the amount of anti-wear protection it offers to the different components of the engine. The zinc decomposes when exposed to heat, creating an anti-wear film that protects the metal surfaces it touches from damage. The film reduces the metal-to-metal contact between the engine’s parts, reducing wear and tear on these parts.

The protection that high-zinc motor oil offers is very important for older engines, especially those with flat tappet camshafts and those designed to generate a lot of horsepower. The reason for this is that the camshaft in a flat-tappet engine operates in a way that creates a lot of friction between its lobes and followers, which in turn builds up a lot of pressure. The pressure squeezes out the motor oil from the followers and lobes. As an anti-wear additive, zinc instead helps the oil bond with the metal and resist being squeezed out. The coating it creates can withstand the high pressures of the engine and keeps everything moving smoothly.

Drawbacks of High-Zinc Motor Oil

As great as high-zinc motor oil seems, it unfortunately does have a major drawback. There’s usually a tiny bit of oil that gets into the engine’s combustion chamber. The zinc in the oil burns up into ash, which goes down the exhaust pipe and into the catalytic converter. The ash coats the components of the catalytic converter, making it less effective and possibly leading to premature catalytic converter failure. This is problematic for modern vehicles since government regulations mandate a service life of over 100,000 miles for catalytic converters. Today, no oil approved for on-road use contains any zinc.

Why Zinc Is Necessary in Older Engines

So if there are clear drawbacks, why use high-zinc motor oil at all? While modern engines have no problems working on modern motor oils, it’s important to remember that older engines were designed in different times. V6 and V8 engines manufactured before 1988 were designed to run using motor oil with zinc in it.

Vintage vehicles will often have engines outfitted with flat tappets, which require zinc oil additives or alternatives to run smoothly. The friction and heat levels generated by a flat tappet engine are much higher than those from the roller camshaft engines of later years. This friction and heat can easily wear down the camshaft, resulting in a loss of engine efficiency and performance if the components aren’t protected by high-zinc motor oil.

Once engine technology began to evolve past the need for zinc additives in motor oil, manufacturers started to produce formulas that either reduced or removed the zinc entirely. That’s why you’ll notice that the standard motor oils you see on store shelves have no zinc in them at all.

The lack of zinc in these oils means using them in classic engines is a bad idea since they can’t provide that extra layer of protection. Some engine oils designed for racing use do have zinc, and those are possible options. Some manufacturers also offer zinc alternative additives in their motor oils. In general, if you want a motor oil for your vintage vehicle, you’ll want to select a high-zinc motor oil that has between 1,000 and 1,400 parts per million (ppm). This number should be somewhere on the packaging. You can also try to find a motor oil formulated with zinc alternatives that offers the same level of protection.

Street Oil Vs. Racing Oil

Racing vehicles also commonly use high-zinc motor oil. Race car engines are always under a lot of stress when they’re running, so their metal components need as much protection as possible. Sulfur and phosphorus are typically also found alongside zinc in high-end racing oils. However, the American Petroleum Institute (API) placed restrictions on phosphorus and other additives in engine oil for road cars.

While motor oils with high zinc content certainly helped engines in the old days, there’s no question that they’ve been pushed out of the limelight in the modern age. Engines have evolved past the need to rely on zinc additives in their oil, but that doesn’t mean zinc itself doesn’t still have a niche in the market. There’s still a demand for high-zinc motor oil for classic cars and race cars, after all. And while there are now alternatives on the market, zinc isn’t completely out of fashion just yet.