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Converting to Synthetic Motor Oil, Break-In Process & Common Myths

Converting to Synthetic Motor Oil, Break-In Process & Common Myths

Uncover the many myths about converting from conventional to synthetic motor oil and learn more about the engine break-in process.
Dave Mann
March 29, 2024
5 min read
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Converting to Synthetic Motor Oil, Break-In Process & Common Myths

Top Insights

  • In my experience as a former Ford Engineer, there are no real concerns when converting to synthetic oils.
  • I recommend a brief initial use of factory-filled petroleum oil for the first 500-1000 miles on new vehicles.
  • I highlight AMSOIL's suitability for new engines, debunking myths and pointing to high-performance vehicles factory-filled with synthetic oil as evidence.
  • I recommend flushing the engine with AMSOIL engine flush as soon as possible to remove sludge, ensuring an optimal transition to synthetic motor oil.
  • Based on my technical expertise, I clarify that synthetic oils do not cause seal leaks but reveal existing faults, with a suggestion to address any leaks or use a higher viscosity oil in older engines.

Meet The Author

“Hi, I’m Dave - a former Ford Truck/Automotive Engineer and the face behind Performance Oil Technology. My trucks, heavy equipment, farm and powersports vehicles experience extreme use, and I use AMSOIL products in every single one; learn more about me here. Have a question? Contact me here. Enjoy the site!”

Common Questions I Get

Some of the most frequent questions I am asked about synthetic motor oils are what is required to convert to synthetic oil, how long I have to wait before installing synthetic oil in a new engine (break in process?), and what I can expect to notice once I have converted to synthetic oil.

Converting to Synthetic Oil - My Recommendations

Converting a vehicle to synthetic motor oil is simple. However, there are a few things you need to be aware of. First, if you have a new vehicle, I recommend that you run a short cycle (typically 500-1000 miles or to your first scheduled oil change, whichever you choose) of the manufacturer's factory fill petroleum (conventional) oil on a gas engine passenger car or light truck (on diesel truck engines this value is typically longer and is usually stated in the owner's manual by the manufacturer of the vehicle and/or engine).

This doesn't mean that you can't install synthetic oil sooner (some manufacturers install synthetic oil as a factory fill). It simply means these are my recommendations based on my extensive engineering work and knowledge of this topic as well as the practicality aspect of it. It doesn't take long to rack up 500-1000 miles on a vehicle. If you don't want to run the petroleum oil for 500-1000 miles you can drain it sooner and change to synthetic oil or you can continue to run the factory fill oil to the first scheduled oil change. It is not as big an issue as some people make it seem to be. The 500-1000 mile figure is very general. There is no set cast-in-stone mileage recommendation that you must or must not convert to synthetic oil. Contrary to what many people believe, synthetic oil will not prevent your engine from properly wearing in. For example, some synthetic oil manufacturers publish recommendations on when an engine can be converted to synthetic oil. 

AMSOIL's Recommendations for Synthetic Oil Conversion

Here are AMSOIL's recommendations:

"Regarding the use of AMSOIL Synthetic Motor Oils in brand new or rebuilt engines, AMSOIL synthetic motor oil can be used during break-in trouble free. In fact, vehicles such as the Dodge Viper, Chevrolet Corvette, all BMW vehicles, all Porsche vehicles, Mercedez Benz, 4 Cadillac models, Pontiac GTO, Harley Davidson Screamin Eagle motorcycles, and many others come factory-filled with synthetic oil. However, since most new vehicles come filled with petroleum oil, it only makes good sense to change to AMSOIL at the first scheduled oil change interval. New engine components generate high levels of wear metals and can contain contaminants from assembly. By allowing the engine to operate with the petroleum oil until the first oil/filter change interval, the wear metals and contaminants are removed prior to installing AMSOIL. There are a couple primary reasons for this recommendation.

  1. New engines or engine components generate high wear metals to begin with and generally contain debris from machining and assembly. It is more beneficial to allow these wear metals to collect in an inexpensive motor oil than to circulate throughout the crankcase for extended periods in a synthetic motor oil. By operating the vehicle to its first drain interval with a petroleum oil, these wear metals and manufacturing debris collect in the oil and are then flushed out of the crankcase when drained. This allows for a much cleaner operating environment for the synthetic lubricant.
  2. Within the first miles of operation, if there are any defects in the assembly or workmanship of the engine components, then they may be corrected before installing the more expensive synthetic motor oil. Occasionally, rebuilt engines may have re-machined components or materials, which can sometimes be mismatched. These problems will develop in a fairly short period of time. If excessive oil consumption or any other problem is noted, this should be corrected prior to changing to AMSOIL Synthetic Oil. For racing applications, a synthetic motor oil can be installed right away. These engines are frequently disassembled and rebuilt under more exacting conditions and require the improved wear protection of a synthetic motor oil. Extended drains are rare due to contaminants such as fuel dilution and dirt entry are common, therefore we would recommend oil analysis to determine serviceability of the lubricant."

Engine Break-In Process & Myths

Today's modern engine designs and manufacturing and materials technology is much more sophisticated than in years past. Regular gas-engine passenger cars and light truck engines do not require the extensive break-in process many people think they do.

In addition, by the time you get your new vehicle, the engine has already been through a series of hot tests also run on in-plant chassis roll testers to check the functionality of all systems and then driven around the plant and railhead to get the vehicle to the dealer, which also helps accelerate breaking in of the engine.

The engine break-in issue is the subject of much controversy, as everyone seems to have an opinion on when an engine is fully broken in, yet they rarely have any documentation or facts supporting their opinion. The information I provide is based on the results of engineering work, many years of experience, and teardown analysis on test engines from all types of vehicles and equipment.  

The differences between an engine that is fully broken in and one that is not can be complicated to detect except in all but the most extreme situations by an experienced engineer with instrumentation, and there is no consumer in a production car or light truck that would ever be able to tell the difference.  The subject of tribological concepts of wear and review of the data can be the subject of a separate article; therefore, what I cover in this article is only the essential points you need to know.

What does breaking-in an engine mean?

The meaning of breaking in an engine is a process of wearing in the pistons/cylinders/rings, bearings, valves, camshaft, lifters, rockers, etc.  In addition, part of the breaking-in process is not only wearing in and seating the internal engine components but also stress relieving the components as well.

Crankshafts, connecting rods, pistons, blocks, etc., have many stresses due to the casting or forging and machining and welding processes. I have viewed and measured these stresses, called fringes, using laser holography.

These stresses are properly reduced/eliminated by costly and time-consuming heat aging, shot peening, and/or high-frequency vibration on a very specialized bedplate for an extended period of time. For production applications, this is cost—and time-prohibitive.

Therefore, the next best thing is exposing your engine to multiple heating and cooling cycles under various loads and RPMs, which is described in the following paragraph. The heating and cooling break-in process continues over a period of time and does not need to be run on petroleum oil. My general recommendations are to run the factory-installed petroleum oil for the first 500-1000 miles or your first scheduled oil change, whichever you choose.

Then drain the oil, remove the factory-installed oil filter, and then install a premium quality synthetic motor oil and a premium quality oil filter, and you're ready to go. Again, I want to clarify that synthetic oil will not prevent your engine from properly wearing in, and you can most certainly convert to synthetic oil sooner than 500 miles if you desire. Further heat cycling break-in will continue during the multiple heating and cooling cycles from driving your vehicle under varying RPM and engine load conditions and by shutting it down for a period of time to let it cool. The multiple heating and cooling cycles are an

important and often overlooked factor in the break-in process. These heating and cooling cycles achieve what is called stress relieving. Back in the "old days" of engine manufacturing, after casting and before an engine block was machined, it would be set outside for several months to age, during which stress relieving occurred naturally, then the block was machined, which helped to produce a better engine than one that was machined immediately after casting.

By changing the factory installed oil and filter around the first 500-1000 miles, or the first scheduled oil change, you will also be removing the initial wear-in particulates present in the oil and filter. The reason for this is that during initial wear-in there is very high particulate contamination in the oil. These particulates consist mainly of microscopic particles of aluminum, chromium, copper, tin, bronze, lead and iron, plus soot particles and other by-products of combustion in your oil.

The oil filter cannot filter out all these small particulates since many are sub-micron size and too small for the filter to trap, but they are also small enough to fit between bearings and other internal clearances and potentially cause wear. That is why I recommend in order to properly wear-in a new engine, perform the first oil and filter change at about 500-1000 miles, or the first scheduled oil change, whichever you prefer and feel comfortable with.

Personally, I convert my new vehicles and equipment to synthetic as soon as possible, within the first 500-1000 miles, or at about 25-50 hours on tractors and certain equipment operated by the hour in order to achieve the benefits of the synthetic oil without waiting for my first scheduled oil change. Small engines such as lawn and garden equipment, generators, and power washers can be changed over sooner.

Flushing The Engine

In a new engine with low miles (up to about the 15,000-mile range), it is not imperative that engine flush be used, although I still recommend it. In an engine with more than 15,000 miles that has been using petroleum oil the entire time, I highly recommend using the AMSOIL engine flush. The AMSOIL engine flush will remove petroleum oil sludge and varnish deposits from your engine and adequately prepare it for synthetic motor oil. You pour in one can (16 ounces) for every 5 quarts of sump capacity (one can is sufficient for most all passenger cars & light trucks, except diesels), and let the engine idle for about 15-20 minutes, then drain the oil and remove the filter while the oil is still warm. Do not drive the vehicle with the engine flush installed.

If you have an extremely contaminated or high mileage engine, I recommend installing a new engine oil filter before adding the flush so that you have full capacity of the filter available for capturing and holding the dirt particles that the flush removes.  Not all engine flushes are created equal. I use and recommend AMSOIL Engine Flush. It is a detergent-based flush with some kerosene and other petroleum distillates that act as the carrier for the flushing and cleaning agents.  The detergent used is 2-butoxyethanol, glycol ether, and is a very concentrated form of detergent used in motor oil. What happens when you operate an engine on petroleum oil is that the sludge and varnish deposits that occur as a result of using petroleum oil will accumulate around your pistons, rings, seals, valve train and other internal engine components and actually help to seal your engine.

This type of petroleum oil deposit sealing can lead to problems such as piston ring sticking, sludge deposits in valve covers and oil pans which can lead to decreased oil pump capacity output and restriction of critical oil galley passageways over an extended period of time, plus many more issues which I will not go into detail in this article.

These deposits are detrimental to the proper operation and longevity of your engine. What occurs during engine use over a period of time is that synthetic motor oils, due to their natural cleansing properties and high detergency, will clean sludge and varnish deposits out from your engine, both the highly accumulated deposits as well as the sub-micron deposits which have accumulated in the microscopic valleys of the aluminum, copper, iron, etc. engine components. Therefore, if you do not use the engine flush a premium quality synthetic motor oil will do essentially the same thing the flush does but take a longer period of time and could possibly necessitate a filter change sooner than normal.

During this time, which is greatly accelerated when using engine flush, the engine goes through a phase where these deposits are being removed or have been removed. What exists now is that these microscopic valleys in the iron, aluminum, copper, etc, are now empty. It takes some time for the molecular structure of the synthetic motor oil to fill these microscopic valleys. This can be as short as a few hundred miles or as long as a few thousand miles, depending on the internal condition of your engine. During this phase you may, or may not, notice slightly increased oil consumption but only until the uniform molecular structure of the synthetic motor oil can re-seal these microscopic valleys.  Most

people do not even notice this phase, but I like to make people aware of it so they understand this process. This is perfectly normal, and the oil is doing exactly what it was engineered to do. Additionally, synthetic oil is much less volatile than petroleum oil, which will result in reduced oil consumption. 

Does synthetic motor oil cause engine seals to leak?

You may have heard the myth that synthetics cause engine seals to leak. Synthetics absolutely do not cause seals to leak, they simply may only possibly reveal an existing leak path and a seal that has failed and is in need of mechanical replacement. Either the seal lip is worn down or the seal is hardened and cracked from old age, heat and ozone. If you have an older higher mileage engine that has been running petroleum oil for its entire life, and it also leaks, for example around the rear-main oil seal, then chances are it may leak the same or possibly more with synthetic oil.

Synthetic oil is naturally cleansing and high detergent and will remove internal engine sludge and varnish deposits, but synthetic oil does not cause leaks. This is commonly referred to as a false seal. Synthetic motor oils are recommended for use in mechanically sound engines. If you have an engine that leaks oil excessively, then repair the seal prior to converting to synthetic oil. The sludge and varnish accumulation inside an engine is highly detrimental to its proper function and longevity and the miniscule "benefit" you may get from it helping to seal a faulty seal does absolutely nothing for your engine. If you have an older engine with a faulty seal and don't want to change the seal but still want to use synthetic motor oil, then I recommend a higher viscosity, such as a 10W-40 instead of a 30-weight oil.

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