What is Break-In Oil & Why/When Should It Be Used?

Keeping an engine up to date is a consistent fight against deterioration. This wear on your engine can lead to not only costly damage, but a reduction in compression—which can compromise your engine’s power. The natural aversion to wear, then, makes it difficult for many to realize that “controlled wear” during the break-in of a new or reconstructed engine is vital in maintaining the life of an engine.

So what is break-in oil?

Break-in oil is created specifically to seal piston rings to the cylinder wall for ideal compression and power from your engine. Break-in oils utilize traditional base oils without additives that modify friction, which leads to the aforementioned “controlled wear” between rings and cylinder wall.

Break-in oils also have phosphorous and zinc additives to help during break-in to protect the camshaft and other components.

What is the difference between regular oil and break-in oil?

Break-in oil, by its definition, is formulated specifically to assist the rings in wearing down of peaks on the cylinder wall to form an exceptional seal in the long-term. Traditional motor oil is, of course, designed to prevent wear.

What is the benefit of using break-in oil?

To fully understand the benefit of using break-in oil, let’s explore “controlled wear” a bit more. 

Sealing piston rings while breaking in engines means allowing the rings and piston skirt to gently wear down the peaks (referred to as asperities) on the wall of the cylinder. 

Even though a new cylinder looks smooth, it actually has several tiny peaks and valleys. If these valleys are too big, they will collect too much oil, which burns during combustion and can lead to oil consumption. At the same time, these sharp peaks do not allow for enough space for the rings to seat firmly, which means the highly-pressurized combustion gases can blow into the crankcase. This taints the oil and also decreases possible horsepower.

Controlled wear assists in flattening to asperities on the cylinder wall, increasing the surface area of the rings to seat tightly. The end result is maximized compression (power) and minimal consumption of oil. Learn why Jesse Prather, championship engine builder, insists his customers to use AMSOIL Break-In Oil in his engines.

Breaking in the camshaft

Another reason to break-in an engine is to harden (or season) the flat-tappet cam.

A flat-tappet cam can wear out more quickly than roller-cam relatives, especially in engines that have more high-tension valve springs. Lobes or tappets that are worn can negatively impact valve lift and duration, both of which reduce engine power and efficiency.

In serious cases, high pressure can disconnect material from these lobes and deposit it in the oil, where it can circulate through the engine and lead to destruction. The use of break-in oil helps to strengthen the camshaft so it’s more wear-resistant.

So how can we allow controlled wear to the cylinder wall and piston rings while also keeping the camshaft safe against wear? 

ZDDP = camshaft protection

The answer is to utilize an ideally-formulated break-in oil that has conventional base oils in addition to high-quality ZDDP additives.

Conventional base oils are produced to have a thinner and less resilient protective film on engine parts, as compared to their synthetic high-quality counterparts. This thinner consistency permits effective controlled wear on the ring/cylinder wall interface. What about the cam—will it be affected by this wear, as well?

This is where additives make a big impact. Zinc and phosphorous additives for anti-wear (commonly known as ZDDP) are activated by heat, which means they offer additional protection in friction-heavy areas—in this case, the cam lobe/tappet area. Additives like ZDDP create a layer on parts surfaces which absorbs contact and aids in resisting cam and tappet wear.

As a general rule, an acceptable break-in oil should contain, at minimum, 1,000 ppm ZDDP. AMSOIL break-in oil, however, contains 2,200 ppm zinc and 2,000 ppm phosphorus.

So when should I use break-in oil?

Everyday drivers with cars or trucks that are new do not need break-in oil. Usually, the manufacturer will instruct you to operate under light-to-moderate load for a couple hundred miles, then change your oil. After this, you are all set. 

Racers, competitors or gearheads who are using a new crate engine or have rebuilt their engine should use break-in oil, following the directions of the engine builder or the crate engine instructions.

How long should I run break-in oil?

Another rule of thumb encourages you to season a flat-tappet cam by running the engine above 2,500 rpm for 15 minutes. When it comes to seating the rings, we have learned through our testing that it can take as few as seven dyno passes, all dependent on the engine, ring tension, cylinder hone and other factors.

Jesse Prather used to run an engine for 2–3 hours on the dyno to properly seat the rings, and sometimes they didn’t seat at all. Using AMSOIL Break-In Oil helped reduce that time to only 10–15 minutes.

If you do not have access to a dyno, follow recommendations of the engine builder or manufacturer. If these are not provided, follow the break-in oil label recommendations.

We recommend running the engine under light-to-moderate loads for around 500 miles. Once again, this is a general rule of thumb, but break-in should not surpass 1,000 miles.

Next, drain the oil, install your preferred synthetic oil and continue driving.

An engine dyno gives you the best method of knowing precisely when the rings are seated. You will feel a surge in horsepower are they begin to seat, and the horsepower will steady as the rings seat. Learn 5 Ways to Boost Your Horsepower for Under $500. Performing a leak-down test is another option.

An additional, more comprehensive method to check if the rings are seated is to take the exhaust headers off and check for oil residue in the exhaust ports.

Oil is an indication of burning oil in the engine, which means the rings are not totally seated. Once the residue has gone, this means the rings are seated properly.

Should I break-in powersports engines?

Consider these questions about your motorcycle, ATV or other powersports application before reaching for a break-in oil:

1. Is the clutch wet?If yes, the break-in oil may not be compatible with wet clutch, decreasing performance.

2. Does it share a sump with the transmission?Several motorcycles use only one oil to lubricate the engine, transmission and primary chaincase. The grinding of transmission gears, especially in high-RPM situations, can rip apart (or shear) the oil if it’s not specifically meant to handle that stress. Using a break-in oil that is not formulated to handle high-shear applications can cause destruction.

3. Does it have a dry sump? Many motorcycles keep motor oil in a separate tank from that of the engine. Leftover break-in oil can gather in the system after the break-in time and contaminate the service-fill oil. In this instance, make sure you run the engine long enough that the oil completely circulates through the system and change the oil to make sure the break-in oil is fully gone.

If you are facing any of the above issues in your powersports engine, we recommend you use your normal motor oil to break in a rebuilt engine.

Run it to the original equipment manufacturer’s (OEM) specifications for new engines, and then change the oil—in other words, run it like you would a new engine right from the factory. If your engine is new, follow the OEM guidelines.

They usually recommend a shorter time period before the first oil change to keep wear particles and factory contaminants as less of an issue. Then pick the best AMSOIL synthetic motor oil for you and continue operating.