Some facts about engine oil

1. Oil additives wear out.

Technically, oil does not wear out. However, extended use causes an oil’s additives to wear out or become depleted. For example, an ashless dispersant oil is designed to suspend dirt and metal particles picked up from the engine. Eventually the oil will become "over-suspended." The principal reason oil is changed at regular intervals is to rid the engine of these suspended impurities. Old oil, with a high degree of contaminants, can cause bearing corrosion and deposit buildup. It can also get to the point where it will not suspend the additional particles created during engine operation. This produces particle buildup or sludge. Overworked oil will also result in the depletion of its other additives. The result is that it will be unable to perform with the benefits the additives were designed to provide.

2. Oil removed during an oil change should appear dirty.
If an oil is doing its job properly, it should suspend dirt, metallic wear materials, and unburned carbon. Therefore, when you change your oil it should look much dirtier than it did when first added to the engine. An excellent method for monitoring an oil’s condition is through oil analysis, which can be key to any preventive maintenance program. Oil analysis must be conducted regularly to establish trends of operation. It provides information on wear metals, viscosity integrity, fuel dilution, and air intake system leaks, among other things. As a long-term preventive maintenance tool, it will build a history of the engine’s performance and aid in the detection of possible problems before they become severe.

3. Automotive oil should never be used in an airplane engine.
The most important reason not to use automotive oil in an aircraft engine is the number of additives in it that are designed for use in water-cooled engines operating within a certain range of temperatures and pressures and at constantly changing levels of power. Aircraft engines are air-cooled and operate under an entirely different set of parameters. This is for people who think all oils are the same.

4. An oil’s viscosity is key to its performance.
Viscosity plays a key role in preventing engine wear and is also important at low temperatures for pumpability. Viscosity determines how easy it is for oil to pump and move through lines and passages. The oil must be thick enough to keep moving parts from contacting each other, and thin enough to permit adequate flow and minimize viscous drag.

5. Using a multiviscosity oil can decrease oil consumption.
It has been found that multiviscosity oils will reduce oil consumption rates. The three ways oil leaves an engine are base oil evaporation at high temperatures, leaks, and blow-by past the piston rings during operation. Because base oils for aviation lubricants are not formed from light base stocks, the evaporation factor is negligible. Multiviscosity oils do not thin out as much at high temperatures, helping to prevent excessive blow-by and/or leakage.

6. Multiviscosity mineral AD oils can be used to seat new piston rings in a newly replaced cylinder.
Just as it is true that a multiviscosity mineral AD oil, such as 20W-50 can be used during engine break-in, it can also be used to seat piston rings in a new cylinder. In fact, it is a good practice for the operator to continue using a multiviscosity AD oil after the cylinder has been replaced because the cylinder will run hotter until the piston rings have seated. Engines run hotter during a replacement cylinder’s ring seating process just as they do during the initial engine break-in period. This is due to increased friction between the cylinder bore and the piston rings and less heat transfers to the cooling fins. The metal-to-metal contact necessary for ring seating causes temperatures to rise within the cylinders.

7. Synthetic oils do not show superior performance when used in piston-powered engines.
The decision to use synthetic oils should be based on the expected use of the oil. Since synthetics cost at least twice as much as mineral oil-based products, there is a tendency on the part of the operator to expect them to outperform in all circumstances. In a piston engine environment, however, the favorable properties of synthetic oils are marginal. Supporters of synthetic oils have basically two main claims: one, they increase time between oil changes and second, they improve startability at extreme low temperatures. Synthetic oils will become contaminated just as quickly as mineral oil in a piston engine and synthetics do not show any appreciable difference in wear levels. OEMs do not distinguish between synthetics and mineral-based products for oil change recommendations. With regard to extremely high-temperature operation, very few, if any, piston-powered engines are operated at temperatures that highlight the benefits of synthetic oils.

8. Using a multiviscosity AD mineral oil to break in a factory-new or zero-time overhauled engines will not damage the cylinders.
It is not true, as some believe, that multiviscosity mineral AD oils do not properly break in engines will damage the cylinders. The break-in phase (the engine’s first 10 to 12 operating hours) is, simply, the dirtiest time for an engine. During break-in, the engine’s oil will be exposed to contaminants and break-in wear metals, as well as excess fuel. Over the past 10 years, America’s Aircraft Engines, Inc. (Tulsa, Okla.), has researched and overseen extensive tests on the break-in of engines using multiviscosity mineral AD oils. Using Phillips 66 X/C 20W-50 multiviscosity oil as its research and testing base, America’s Aircraft Engines has determined several key advantages to breaking in an engine with a multiviscosity mineral AD oil:
• Multiviscosity mineral AD oils "seat" piston rings in approximately half the time of a straight grade oil. Synthetics are unable to break-in an engine.
• Multiviscosity mineral AD oils reduce the chance of break-in cylinder glazing, a risk pilots take when breaking in an engine with a straight-grade mineral oil. A straight- grade will often deposit varnish and lacquer in the high engine temperatures reached during break-in. As a result, these materials may collect in the cylinder wall crosshatching and magnify glazing of a marginal cylinder.
• Multiviscosity mineral AD oils, when used during break-in and beyond, provide quicker start-up than straight grade mineral oils. The lubrication provided by multigrade mineral AD oils is more immediate than that provided by straight grade mineral oils.
• A good single or multigrade AD mineral oil will suspend debris that is created during the "dirty" time of break-in, keeping it from being deposited inside the engine. An initial 10-hour drain will rid the system of the contamination introduced during break in.