Does More Zinc = More Wear? The REAL Truth About ZDDP Additives
Lake Speed Jr. from The Motor Oil Geek, in collaboration with Total Seal and RLER Manufacturing, Southwest Research Institute embarked on an investigative study to uncover the true effects of ZDDP (zinc dialkyl dithiophosphate) in engine oils.
Commonly referred to as zinc, this compound is renowned for its protective properties in engine components, but questions remain: Is more zinc always better? Can there be too much of a good thing? This study aims to answer these questions by examining the effects of varying zinc levels on piston ring and cylinder bore wear.
Understanding ZDDP
ZDDP is a polar molecule attracted to ferrous surfaces in engines. Under heat and load, it reacts with these surfaces to create a sacrificial film that helps prevent wear. This film acts like snow on a rocky surface, smoothing out the microscopic peaks and valleys, increasing contact area, and protecting the metal beneath. However, it’s crucial to note that while ZDDP reduces wear, it does not reduce friction; in fact, it typically increases it. Friction and wear are independent phenomena, and reducing one does not necessarily reduce the other.
The Goldilocks Zone of ZDDP
Finding the right amount of ZDDP is critical. At low levels, adhesive wear occurs because there isn’t enough ZDDP to form a protective film, leading to scuffing and scoring. As the ZDDP level increases, wear decreases up to a point. Beyond this optimal level, excessive ZDDP leads to corrosive wear. Thick films formed by high ZDDP levels can slough off under load, taking the underlying metal with them, much like thick paint peeling off easily compared to thin paint.
Real-World Implications
A real-world example highlights the dangers of excessive ZDDP. A customer broke in an engine with oil containing 1,200 parts per million (ppm) of ZDDP. After a successful 30-minute run, they switched to an oil with 3,600 ppm of ZDDP, which led to camshaft failure within five minutes. This underscores that too much ZDDP can be detrimental, increasing wear rather than reducing it. Hence, it is advised not to use ZDDP additives indiscriminately, as the right balance is essential.
Experimental Results
To illustrate the effects of ZDDP on wear, the researchers used a TE77 reciprocating rig to simulate engine conditions. They tested oils with different ZDDP levels on piston rings and cylinder liners with varied surface finishes and materials. The oils tested included a high-ZDDP break-in oil, an API SP oil, and a high-performance oil.
The results showed that the break-in oil with high ZDDP levels produced more friction but less wear, while the API SP oil had lower friction but higher wear. This confirmed that higher ZDDP levels provide better protection against wear but increase friction due to thicker protective films.
When the researchers changed the ring and liner surfaces but kept the oils the same, they observed significant differences. The smoother surfaces and different ring materials reduced wear dramatically, even with the same oil. This demonstrated that the interaction between oil, surface roughness, and material composition is crucial in determining wear and friction outcomes.
Conclusion
The study concluded that there is no one-size-fits-all solution for engine oils. The optimal ZDDP level depends on the specific engine application, including the metallurgy and surface finish of the engine components. Tribology, the study of friction, wear, and lubrication, reveals that the right oil formulation must consider the entire additive package and not just the zinc content.
The researchers emphasized that while oil marketing often promotes products based on ZDDP levels alone, the true performance of an oil can only be determined by considering how it interacts with the engine’s materials and operating conditions. This comprehensive approach ensures that engines receive the best protection without the risk of excessive wear from too much ZDDP.
In summary, the key takeaway is that more ZDDP is not always better. Understanding the balance and the specific needs of your engine is essential for optimal performance and longevity.
