The Truth About Zinc & Motor Oil


While you may think the whole Zinc issue has been beaten like a dead horse, the reality is that very few people actually understand what has changed in motor oils over the last decade. The real problem lies in the fact that these same people are the ones who stand to suffer from these changes. Typically, the average hot rodder or racer knows the least about the motor oil going into that very expensive engine.

While many professional engine builders know that motor oils have changed, many of them would not know the difference between ZDTP and ZDDP.

What’s that you ask? Isn’t all Zinc the same? Let’s get the facts straight about Zinc.

When we talk about “Zinc” in motor oils, what we are really talking about is a family of additives called Zinc DiakylDithioPhosphates – better known as ZDDP.

Many different types of ZDDP additives exist – Primary, Secondary, and Ary. These different types of Zinc have different activation thresholds. You see, Zinc is not a lubricant until the ZDDP reacts under heat and load to create a phosphate glass film that protects the metal surface.

This is critical to protection.

Zinc needs heat and load for it to activate and then lubricate the surface. Some types of Zinc activate faster under less heat and less load than other types of Zinc. These “fast burn” Zinc additives provide better protection during engine break-in because they react faster and establish that protective Phosphate glass coating quickly during the critical break-in phase.

All types of ZDDP function in the same manner. Zinc is a polar molecule, so it is attracted to steel surfaces. Under heat and load, the Zinc reacts with the steel surface and creates a phosphate glass film that protects the steel surface by forming a sacrificial film that covers the peaks and fills in the valleys of the steel surface.

How much heat and how much load is required to activate the Zinc depends on the type of Zinc in your oil. Secondary ZDP is the most active type of Zinc, but it is also blamed for reducing catalytic converter life. Newer, less active ZDPs are being used in the API SN and GM dexos 1 oil specification in order to meet increased demands on catalytic converter life. This means the type of zinc used in your favorite brand of oil may have changed, if you are still buying oil for you hot rod at the big box retail store.

This new, less active Zinc was introduced in 2010 for the 2011 model year cars and trucks.

Are you ready for some good news? The key to how much and what type of Zinc your engine needs depends on your engine’s valve train. If you have a stock valve train and no other performance modifications, then an API licensed oil is all you need. Every API licensed oil will protect stock engines under normal street driving cycles.

When you start making performance modifications or begin racing, everything changes.

Higher lift cams with longer durations and greater spring pressures need a faster response from the Zinc. Oil development in race engines shows that faster acting ZDTP does a better job protecting highly loaded valve trains. Basically, the Zinc package needs to be optimized for the application, and this is where the confusion happens.

Many people have had good success with premium API licensed products in stock engine applications (as well they should). However, this can create a false perception that API licensed oils should work in every application, but this is simply not the case. When you go beyond normal valve lift, operating temperatures and cylinder pressures, the oil formula needs to adapt to these “new” requirements.

Because the modifications fall outside the OEM guidelines used by the API to determine oil performance specifications, an API performance level does not apply. This leaves the consumer in the dark. If that knowledge leaves you feeling less than confident, then you may not want to learn about detergents and dispersant additives in motor oil that actually compete against the Zinc in your engine.

That’s right. Zinc is not alone in your motor oil. Several other additives like detergents, dispersants, viscosity index improvers, and others all compete against the Zinc inside your engine – sometimes with negative consequences.

Back in August of 2005 (less than a year after API SM was introduced), the Society of Tribologists and Lubrication Engineers published a story stating that calcium-based detergents and dispersants competed against the ZDDP for surface space, and that caused some wear issues in passenger car engines. Around this same time many engine builders began to experience a rash of flat tappet cam failures during break-in.

The level of ZDDP had also been reduced in the API SM oil spec, and along with the increased use of calcium detergents and dispersants, the critical balance had shifted. The results were nearly catastrophic for independent engine builders and camshaft manufacturers. The rate of flat tappet cam failures escalated at an alarming rate.

The decrease in ZDDP from 1,000 ppm down to 800 ppm was called out as the cause for the rash of cam failures. This failed to take into account the change in ZDDP to detergent balance. Many engine builders switched to diesel oils that contained higher levels of ZDDP, and that worked sufficiently until the diesel oils underwent a reduction in ZDDP down to 1,200 ppm in October of 2006. By the end of 2007, engine builders were again on hunt for a higher Zinc solution. This time, many switched to properly formulated break-in oils high in ZDDP and low in detergent. Some still held onto the diesel oils, but also added an off-the-shelf ZDDP supplement.

This supplement is a step in the right direction, but it still fails to address the abundance of detergent during break-in. Plus, who knows what type of ZDDP you are adding. Is it fast burn or slow burn ZDDP?

Having the right balance of additives is the key to application-specific protection and performance.

Here are the facts as they relate to off the shelf motor oils:

-Prior to 1993, the ZDDP content of motor oil was not limited.

-By 1996, the ZDDP content was limited to 1,000 ppm, but no cam failures due to that level of ZDDP were reported.

-By 2004, the ZDDP level was down to 800 ppm in API SM licensed oils. This was mandatory for API licensed oils that were SAE 10W-30 or less. Diesel oils are typically 10W-40 or higher, so these viscosity grades can contain up to 1200 ppm ZDDP in accordance with the API CJ-4 Diesel engine oil standard. However, all of these oils have had increased levels of detergents and dispersants since the late 1990s. This allows for longer drain intervals and helps to keep engines cleaner when they are forced to use exhaust gas recirculation to limit emissions.

All of these changes make sense in the context of modern passenger cars and fleet diesel engines. The problem lies in using these products in applications that they were not designed nr intended for, e.g. racing, track days and hot rodding.

A proper race oil should be designed to protect under extremely intense conditions, and then changed on a regular basis. Good racing oils allow the user to change the oil filter after each weekend event and add fresh oil and a filter as long as the oil still looks to be in good condition. As soon as the oil shows signs of darkening it should be changed.

A proper hot rod oil can go all year long (up to 3000 miles) before needing to be changed. Also, a hot rod oil is designed to protect in the garage as well as on the track. Many hot rods are not daily drivers, so they see extended periods of storage. A good hot rod oil provides storage protection as well as wear protection.

Again, back to that word – balance.

There is a lot of hype over a lot of products, but only one real truth – proper balance is what makes an oil right for an application.

Using Unmatched Lubricants – Additive Clash:


A perfect example of proper balance can be seen is an API SN motor oil. While this spec oil is limited to 800 ppm of a catalytic converter friendly ZDDP, an API SN oil can break in a flat tappet camshaft. The flat tappet cam in question has less than .400 valve lift and no more than 215 psi valve spring pressure. So an API SN oil will protect a flat tappet cam, but you won’t see success trying to break in a Big Block Chevy cam with over .500 valve lift and over 300 psi valve spring pressure with an API SN oil. It is the different demands of the valve train loads that dictate what balance is required to protect.

The bottom line is that bigger lift, longer duration cams with more spring pressure need a proper break-in oil to establish that critical anti-wear film. After break-in, a hot rod-style oil for street/strip should be used to maintain that protective Zinc film.  Race applications meanwhile need a proper racing oil to deliver race-specific performance.

A stock V8 may look very similar to a hot rod V8 or a racing V8, but in reality each of these applications needs a different balance to provide the proper protection for the investment.

The good news is that specialty oils are now available that provide the application- specific protection performance engines need, letting you choose the correct oil for  your engine every time.

Using the Driven Racing Oil System:

Driven Racing Oil Engine Assembly Grease places “Fast Burn” anti-wear additives on the critical wear surfaces of your engine, and the Driven BR Break-In Oil provides the correct balance of “Fast Burn” Zinc additives and low levels of detergents to quickly establish a sacrificial anti-wear film throughout your engine. Rapidly establishing this anti-wear film in your engine provides a lower wear break-in and extends engine parts life.

For example, using the system of Engine Assembly Grease followed by the BR Break-In oil and then using XP1 Synthetic Racing Oil, allowed Joe Gibbs Racing to double flat-tappet lifter life from 600 miles to 1200 miles!

Driven Assembly Grease followed by Break-In Oil and then Synthetic Racing Oil or Hot Rod Oil like the primer, sealer and base color of automotive paint. It really does make a difference when you apply the right products for the job in the correct order!

Regardless of the lubricants you use, it is of vital importance that you properly prime the oiling system before starting a new or re-built engine. Please follow your camshaft manufacturers’ break-in procedure for flat-tappet camshafts.

Information and charts are property of Driven Racing Oil and cannot be duplicated without permission.

Zinc vs. Detergent >

Engine Builder Lubrication Guide >