Zinc Additive for Oil—How Much ZDDP is Enough

By Jefferson Bryant 8/12/ Share Add Article To List

Your freshly-built engine is finally done. You sent the block out to get machined, along with the crank, rods, and pistons. You spent hours dialing in your ring gap and measuring the tolerances to get it exactly where you want it. It is now fully assembled, along with that new flat-tappet solid-lifter cam that will rattle the fillings out of pedestrians on the sidewalk. Everything is loaded in the engine bay, all the wires connected, ready to fill the pan with oil, prime the pump, and fire it up. You grab six bottles of your favorite oil and dump them in. Next thing you know, the engine isn’t sounding right halfway into the break-in, and then it is running really rough. You shut it down and drain the pan only to find enough glitter to supply a kindergarten class for a month. You already know the problem- a cam lobe went flat during break-in.

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This is a common issue when using modern oils in older engines. In , oil manufacturers started reducing the amount of zinc and phosphorous in motor oils. This was due to the fact that both zinc and phosphorous have a bad habit of damaging catalytic converters. Inside a catalytic converter is a mesh coated in platinum; the zinc and phosphorous bond to this layer of platinum, making it much less effective at burning off contaminants. This is less of an issue for modern engines with roller camshafts and stock internal parts, but in older engines with flat-tappet cams or modern engines with aftermarket internal components, it is a big problem.

Why Do I Need Zinc Additives for Flat-Tappet Cams?

Engine oil breaks down at about 260 degrees, synthetic lasts a little longer to 300 degrees. The heavy rotating assembly components in your engine can reach 400 degrees during normal use; by the time the bearings and machined surfaces reach 400, the oil is no longer functioning as it should. Luckily, your oiling system keeps the oil moving, so there is always cooler oil moving in, pushing out the cooked oil. ZDDP acts as a heat-activated barrier between the bearings and the machined journals of the cam, rods, and crank. Think of it as two-stage protection for your engine. As the oil begins to break down from the heat, the ZDDP breaks down too. However, this breakdown results in a chemical reaction that protects the metal by acting as a temporary lubricant layer. This layer is most critical in sliding-motion contact where one or both surfaces see constant friction, such as flat-tappet lifters that slide on the cam lobes and piston rings that slide up and down on the cylinder walls. Compared to roller lifters, which have a roller follower that drastically reduces the friction between the two surfaces. That said, even roller cams need a higher level of ZDDP when the valve spring pressures get above 160 lbs closed to 290 lbs open, as this puts additional strain on the cam lobes.

This short video explains why ZDDP and its protection benefits are especially beneficial with flat tappet camshafts

Why Do I need Zinc Additives for Engine Break-In?

When it comes to freshly built engines, flat or roller lifter, the first 30 minutes is the most important for the life of the engine. For flat tappet cams, this is when the lifters are work hardened and set the wear pattern they will have for the rest of their useful life. In this instance, ZDDP actually helps the lifter break in by aiding the traction on the camshaft, this is the spinning action that flat-tappet lifters have; they spin around as they move up and down. If there isn’t enough traction, then the lifters will wear unevenly, which will kill a cam lobe pretty fast. This is one of the reasons you don’t use synthetic oil to break in an engine.

Inside the cylinders, the pistons move up and down, using three rings (technically four rings, one top, one middle, and two oil control wiper rings) to control both the chamber pressures and to keep oil film out of the chamber. When the rings fail, you end up with blow-by, which is oil that gets inside the combustion chamber and is burned. This leaves behind a trail of blue smoke coming out of the exhaust. The rings do rotate slightly on the pistons, but they are in constant contact with the cylinder walls, and this is also a form of that dreaded sliding motion. In the first 500 miles of an engine’s life, the piston rings wear in the cylinder walls in a process called “seating.” The walls of an engine cylinder have microscopic sharp ridges and valleys, which allow both combustion gasses and oil to bypass the rings, creating all kinds of issues.

Oil alone isn’t enough to protect the metal during this particularly brutal phase of operation. The sharp peaks, while microscopic, grab at the ring material creating a shear force. ZDDP acts as a shear lubricant, forming a layer of film that protects the metal surfaces from micro-welding or galling together. Similar to the sliding friction of flat-tappet lifters, the shear force generates enough heat to activate the ZDDP.

Learn more about ZDDP and how it works in this article about What is ZDDP – Benefits of Zinc in Oil.

How Much ZDDP is Enough? How Much is Too Much?

All modern motor oils contain some level of ZDDP, but not enough to protect an older engine, especially during break-in. Most modern motor oils have a maximum of 800 ppm (parts per million) of ZDDP. However, the recommended bare minimum for flat-tappet cam engines and fresh-built engines of all types is 1,000, but most experts agree that 1,200 ppm of ZDDP in your oil is preferred. You must strike a balance on the ZDDP content in your oil if your vehicle has a catalytic converter; this is where the 1,000 ppm level is sufficient. All motor oils have a rating, commonly SH, SJ, and SL. The SH rating was introduced in , and this oil is no longer available and had 1,200 ppm of zinc phosphorous. In , the SJ rating was introduced, and the ppm levels came down to 1,000. The real problems with premature engine wear in older engines and freshly-built flat-tappet engines began in earnest around when the SM rating was brought out, which further reduced the ZDDP levels to a maximum of 800. You can see the oil rating in the API “donut” graphic, which is required to be on the label. The current API rating is SN, rated for vehicles made after . ZDDP additives are sometimes formulated for both conventional and synthetic oils, you do need to verify that product you choose is ZDDP additive for synthetic oil or for conventional oil to match your preferred type of engine oil. Technically speaking, Zinc oil additives for synthetic is actually ZDTP, Zinc dialkyldithiophosphate, whereas conventional oil Zinc is ZDDP, Zinc Dialkylphophate.

For break-in, you want to see a ZDDP level of 1,400-1,500 ppm for at least the first 500 miles. After that, you can reduce the ZDDP level to 1,000-1,200. This is not a situation of a little is good; more is better. It is imperative that you follow the directions on the ZDDP additive. What you absolutely don’t want to do is to add too much ZDDP. Once you get about 1,500 ppm, ZDDP starts having the opposite effect inside the engine and gets corrosive, which can clog up the oil passages and cause premature wear inside the engine.

Best ZDDP Oil Additives- Top 3 Customer rated additives linked below:

COMP Cams 159 Engine Break-In Oil Additive, 12 Ounce

Howards Cams ZPM 4 oz Break-In Engine Oil Additive

Redline Cam Break-In Oil Lube Additive

Adding ZDDP To Your Engine

Using a zinc oil additive in your engine allows you to continue using your favorite engine oil while maintaining an appropriate level of zinc for engine protection.

Break-In

During the engine break-in period, which is the first 500-1,000 miles, the easiest method is using a pre-packaged ZDDP oil additive. This ensures that the oil is adequately formulated to protect your engine in those crucial first moments during the initial startup. You can find pre-packaged break-in engine oil additives at Speedway Motors.

After Break-In

These motor oil additives are designed to be added to modern engine oils to increase the levels of zinc, phosphorous, and molybdenum in the oil. Once your engine has been broken-in, you simply add one bottle of your favorite zinc additive with every oil change. That’s all you have to do to ensure your engine has the best protection.

All engines can benefit from Zinc oil additives, especially during break-in or after a cam swap. If your engine has a flat-tappet cam or aftermarket internal components, you must use a zinc engine oil additive to protect the vulnerable surfaces from damage. While newer modern engines do not have as dire a need for the higher levels of ZDDP, they still benefit from it. Modern API class oils typically provide the necessary levels of ZDDP for the daily operation of modern engines; however, they still require higher levels up to 1,500 ppm for break-in and if your engine has aftermarket performance internals.

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Classic car enthusiasts pride themselves on preserving pieces of automotive history. But when it comes to maintaining those older engines, one topic sparks frequent debate: do classic car engines need zinc-rich oils to function as intended? If you’re restoring a vintage vehicle or hitting the road in one, understanding the unique requirements of these engines and how zinc additives factor into engine oil formulations is crucial.

Let’s explore the role zinc plays in keeping classic engines running smoothly, how it benefits older vehicles, and why modern oils may not always meet the needs of vintage machinery.

Understanding Classic Car Engines

The charm of classic cars isn’t just their iconic designs but also the craftsmanship of their engines, which often differ significantly from the manufactured engines of today. Decades ago, engine technology didn’t have the advantages of modern materials or advanced lubricants that we take for granted. Classic car engines rely heavily on components like flat tappet camshafts and lifters, which have direct metal-to-metal contact. Unlike modern roller camshafts, these components create high-pressure friction zones that require sufficient lubrication to avoid damage.

Older engines operate under conditions and tolerances that make wear and tear a constant risk. With direct contact between metal surfaces and higher friction levels, protecting these engines calls for specific lubrication properties. Without the proper additives in motor oil, surfaces can wear down quickly, leading to costly repairs or irreversible engine harm.

For classic cars to perform reliably, they require a careful balance of effective lubrication and protective agents. This means that when it comes to older engines, oil selection goes beyond viscosity or brand preference; the formulation itself can have a dramatic effect on longevity and performance.

The Role of Zinc in Motor Oil

Zinc dialkyldithiophosphate (commonly known as ZDDP) has long been a critical ingredient in motor oils designed for high-performance and older engines. The main purpose of this zinc additive is to minimize wear and tear, especially in high-friction areas like the flat tappet camshaft. When the engine heats up, ZDDP forms a protective phosphorus-based film over metal parts, reducing contact wear and ensuring the components can move smoothly even under stress.

Without zinc additives present, these vulnerable areas can experience excessive wear, leading to pitting, scuffing, and eventual engine failure. This protective layer is particularly beneficial for classic engines that regularly operate under higher stress levels, making ZDDP a near-essential ingredient for vintage car oils.

However, the benefits of ZDDP come with some caveats. While its anti-wear properties are undeniable, phosphorus—a by-product of ZDDP—can damage catalytic converters over time, which has driven major changes in motor oil formulations in recent years. For classic car owners, though, the preservation and performance benefits of zinc-rich oils often outweigh compatibility concerns because many vintage vehicles lack catalytic converters altogether.

Modern Oils and Classic Car Requirements

One of the biggest challenges in maintaining a classic engine is navigating the difference between modern lubricant formulations and what your vintage vehicle truly needs. Over the last few decades, regulatory changes and environmental standards have led to a significant reduction of ZDDP levels in most mainstream motor oils. Manufacturers craft modern motor oils to meet the requirements of contemporary engines, ensure compatibility with catalytic converters, and focus on cleaner emissions.

For the average modern car, this shift poses no issue. But for enthusiasts of classic cars, this trend introduces real risks. Oils designed for modern engines often lack the sufficient anti-wear protection needed for flat tappet camshafts, leaving classic engines more vulnerable to premature wear and potentially catastrophic engine damage.

Another complicating factor is that newer oils often cater to smaller, more efficient engines, rendering them less compatible with the unique operating conditions of older engines. If you were to rely on these formulations in a classic car, you might notice problems such as excessive oil breakdown, overheating, or premature engine aging. No classic car owner wants to risk these issues.

That’s why many classic car owners turn to specialized or high-zinc oil formulations designed specifically for older engines. These formulations prioritize the anti-wear properties demanded by vintage engine designs, ensuring protection where needed most. Additionally, classic car-specific oils frequently include optimized viscosities, helping them provide consistent performance under the wider temperature ranges that older engines may encounter.

Classic Car Protection

Choosing the right motor oil for your vintage engine is about more than a preference for one brand or another. It’s about understanding what your car’s engine demands to perform at its best. While modern oils meet the needs of contemporary cars, they are rarely suited for classic engines without the protection of zinc additives like ZDDP.

When selecting motor oil, always opt for formulations aligned with the unique friction-heavy requirements of flat tappet engines. Many automotive supply companies cater specifically to collector cars and offer specialized oils enriched with the zinc levels that these engines need. Additionally, pay close attention to oil change intervals. Given the specialized requirements of classic engines, regular oil changes with the correct formula are essential for maintaining optimal performance.

Owners should also educate themselves about their vehicle’s specific make and model. Some later classic cars came equipped with roller cams, which may reduce the reliance on zinc to some degree. However, ZDDP is crucial for most pre- vehicles with flat tappet cams.

Another key consideration is working with a qualified mechanic familiar with classic vehicles. These professionals often bring a wealth of knowledge about what oils work best and can provide recommendations tailored to the specific needs of your treasured ride.

Reinventing Tradition With Modern Protection

Classic cars connect us to a bygone era of craftsmanship, performance, and style. Keeping them in top condition requires care, knowledge, and the right resources. By understanding that classic car engines need zinc-rich oils, you can provide protection where modern oils simply fall short.

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