Break-In Oil - Does Zinc Additive Really Help?

The lifeblood of every engine, oil is far too often misunderstood and incorrectly utilized. Engine oil does so much more than just lubrication, each formulation performs differently in various engine types based on the needs of that particular engine. Diesel engine oils have different detergent additives to handle diesel combustion byproducts, such as soot, while gas engine oils have gasoline-specific detergents. Under daily use, these oils do their job well, but what about under break-in conditions? The first 30 minutes are critical for the engine's life, and then the next 1,000 miles are nearly as necessary, making your choice of oil paramount to a successful build. Whether you are working with a crate engine or one you built yourself, break-in oil is necessary because these oils are fortified with high levels of Zinc phosphate, commonly referred to as ZDDP.

What is ZDDP- Benefits of Zinc in Oil

This is a sliding motion component; the lifter surface slides along the cam lobe. This is the most destructive type of contact. Once broken in, a lifter and cam lobe become one homogenous system, and the two components establish a consistent wear pattern for those two pieces; if you switch the lifter around on the cam, they will burn up almost instantly because the two surfaces do not match anymore. Within that first 30 minutes of break-in, the lifters and cam lobes work harden. If you have ever tried to drill stainless steel, you have likely experienced this phenomenon, it becomes impossible to drill because the steel is rock hard. While the lifter itself is what gets talked about, it is the cam lobes that are worn away in a break-in failure, so it isn’t like you can just swap lifters; the camshaft itself is ruined and has to be replaced.

Flat tappet cam break-in oil protects the lifters and cam by adding a second layer of protection. It does this through heat and friction. Yes, friction. Flat tappet lifters spin in their bores, which helps establish the wear pattern. ZDDP is an interesting chemical, it provides a friction element for traction to generate spin, and when the components reach 300 degrees, the ZDDP protective layer activates and acts as a barrier between the two surfaces as the oil loses its lubricity above 300 degrees.

Roller cams also benefit from ZDDP, but not on the same level as flat tappets.

Controlling the piston ring wear-in process is critical for all engines; in fact, engine break-in is more about the piston rings than anything else. Smoothing out the jagged edges on the cylinder walls is what allows the rings to seat, reducing blow-by and oil consumption.

The goal of the break-in process is to control wear across all surfaces. You don’t want a slippery oil for break-in, so you don’t use synthetic oil for the initial start-up. The brand-new car you buy can have synthetic oil in the engine when you buy it because it has already been broken in; your new crate motor, however, has not been. Even standard conventional oils have friction modifiers in their formulation, inhibiting the break-in process. Flat tappet cam break-in oil helps increase friction in certain areas as required for a complete break-in process.

Break-in oils are typically straight base oil without friction modifiers, and as much as 4000 PPM of ZDDP, which, when used at this level in an engine with more than 1,000 miles, can cause the opposite of protection, as too much ZDDP becomes caustic and causes more wear. For an initial break-in, these levels are not too much, as you are controlling the wear, and the oil is not used for very long.

Some break-in oils list they can be used for higher mileage (up to 4,000 miles). This indicates they have detergents in the formulation to grab onto particles from the break-in process. It is your choice, but most engine builders highly recommend using a non-detergent break-in oil and promptly changing it after the initial 30-45 minute break-in process. The detergency level of your oil is important for the life of your engine, but in that initial break-in, it tends to be more detrimental than helpful.

These also correspond with ILSAC ratings (International Lubricant Specification Advisory Committee), which begin with GF-X; the first rating came out in 1993 as GF-1. Currently, there are three active ILSAC ratings, GF-5 (2011), GF-6A, and GF-6B (2020). The GF-6A and 6B ratings are for specific weights of oil, GF-6B is for 0W-16, and GF-6A covers the rest of the commonly used viscosities.

In 2010, GM released its own oil rating, dexos, which starts as, surprise, dexos1, which is now obsolete. The current level is dexos1 Gen 2. While new modern engines may require brand-specific oil, there is no specific SBC break-in oil for older GM engines or a Ford-only small block Ford engine break-in oil, you just need quality oil from a reputable manufacturer. Most engine break-in oils are only one viscosity- 30 weight, but there are a few brands that offer thinner eights, but most builders agree that straight SAE 30 weight break-in oil is best for that first 30-45 minutes of run time. This is because multi-viscosity oils contain friction modifiers that inhibit the wear-in process. When starting up a freshly built engine, there is such as thing as too slippery.

What does this mean? Quite a lot, and it is really important, but very few people know that they need to be paying attention to the ratings because the newer ratings are not backward compatible, meaning you could end up with engine damage if you used SP, GF6A/B rated oils in a vehicle older than 2020. SN Plus is the most common API rating and is backward compatible with most engines, along with ILSAC GF5 and dexos1 Gen 2. GF-6A is backward compatible for their weight ratings.

For “Classic” engines, such as the SBC (small block Chevy), 10W-40 is often used, as these engines are built with loose tolerances, to begin with, and as they get more miles on them, they loosen up a bit more. 10W-40 is commonly used on original (not rebuilt) engines built before the mid-1990s. There is no ILSAC rating for these oils, these are API SP standards only.

Governmental regulations, as well as manufacturing technologies, change quickly. Just a quick read into the ratings shows how much can change in just a few short years. Metallurgy and tolerances in newer modern engines have reduced the need for ZDDP, in addition to the fact that ZDDP levels above 1000 destroy catalytic converters, which was the main driving force behind its removal from modern engine oil. Many cams have been destroyed because this information doesn’t flow downhill very well, meaning the people who make the rules know it, the engineers know it, but the consumers rarely, if ever, even hear about these changes. I first learned of the issue in 2007 after a cam swap in a Pontiac 455 went south 20 minutes into the break-in, even though ZDDP was first reduced in 1994.