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Looking down the road a bit we see new motor oil specs are coming. One thing you can always count on, whether in business or life, is that change is constant.

Because of the upcoming changes in motor oil specifications, I thought it might be interesting to look back at one of the changes that occurred in our last round of motor oil upgrades, the reduction of zinc and phosphorus levels.

Zinc-based additives are used primarily as anti-wear agents to prevent premature wear of engine components. Zinc dialkyldithiophosphate (ZDDP), which also provides corrosion and oxidation protection, is the most commonly used form of zinc additive.

In 2004 zinc levels were lowered in response the American Petroleum Institute (API) SM and International Lubricants Standardization and Approval Committee (ILSAC) GF-4 oil specifications. The action was driven by original equipment manufacturers (OEMs) based on the Environmental Protection Agency (EPA) mandate that emissions reduction systems needed to function for a specific period of time without failing. OEMs pushed to remove anything in motor oil that could potentially harm emissions reduction systems.

As has been publicized within the industry, reduced ZDDP content has been linked to issues with premature wear in flat-tappet camshaft engines and, in particular, with engines that include high-tension valve springs or other modifications that create high contact pressures. This reduction of ZDDP tends to raise questions that, with assistance from our tech team, I will address here.

Are there other additives that provide the same protection as zinc?

Some premium synthetic oils contain additive packages that replace a portion of the ZDDP component. These motor oils provide great anti-wear protection to the targeted applications. Street-rodders and classic-car enthusiasts many times need or prefer the extra anti-wear protection provided by motor oils containing high levels of ZDDP to protect the flat-tappets common to the engines they love.     

Do you recommend any oil additives for normal operation?

We do not recommend using additional pour-in oil additives. If the motor oil is formulated correctly for the application, there is no need to consider use of any oil additives. Formulating motor oils is a balancing act. Oil additives focused on extreme pressure or anti-wear resistance may appear to initially help with these particular properties, but upset the balance in other areas and can promote acidic corrosion, excessive oxidation and foam.  

Many engine builders recommend the use of diesel oil in vintage/flat-tappet engines, is that a viable option?

The assumption is diesel oils contain high levels of ZDDP that cannot be found in other motor oils. This recommendation is partially correct. First, make sure the diesel oil carries gasoline credentials; some do not. If the diesel oil is recommended for gasoline use and it contains a healthy dose of ZDDP, it may be a viable option. Be careful not to generalize by thinking all diesel oils contain high levels of ZDDP; this isn’t true. Modern API CJ-4 oils have lower levels of ZDDP than their predecessors. If particular oil is in question, send a sample to a reputable oil analysis testing service for a metals analysis.

Are racing oils subject to lowered zinc levels?

The low phosphorus levels required by API SN apply only to 0W-20 through 10W-30 viscosity lubricants. Racing oils are typically higher viscosity and anything above a 30 weight is not required to have low levels of phosphorus, even if it is API SN. Most racing oils are expected to contain high levels of anti-wear protection since durability is their main purpose.

Are racing oils a good option for street-driven performance engines? Why or why not?

That is dependent on the brand and formulation. Racing oils designed exclusively for the track many times do not contain appropriate levels of detergents and dispersants required for longer-term street use. These formulations would not provide adequate protection against engine sludge, rust, oxidation and attack from acids and other combustion byproducts. The best advice is to talk with a reputable manufacturer, ask informed questions and make decisions based on the actual specifications.  

In oils with lowered zinc levels, do higher viscosities provide any better protection?

Higher viscosity oils may help with extra protection, but with flat-tappet camshaft engine applications, especially ones with modifications including high-tension valve springs, a strong anti-wear package is required to protect your customer’s investment.

There’s always risk involved in change. The unforeseen consequences of reducing ZDDP were eventually recognized and addressed. The continuous efforts to meet federal greenhouse gas/fuel economy standards will likely encounter additional bumps in the road when we move to the next API service category. Don’t spend too much time worrying about it. There will be a lot of smart people paying attention to whatever happens, and publications like this one will keep us posted so you’ll know what to do.

ED NEWMAN is the advertising manager for AMSOIL INC., an independent manufacturer of synthetic lubricants. He’s been writing articles about synthetic oil since 1986. He can be contacted at enewman@amsoil.com. For more information, visit: www.amsoil.com


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