Maintainers Corner - Facts about Aviation Oil
The following "Facts About Aviation Oil" were developed by Harold Tucker, Lubricants Technical Director for the Phillips 66 Company; Dr. Alex Schuettenberg, Senior Research Chemist, Lubricants Technical Support for Phillips 66; and by Richard Fowler, President of America's Aircraft Engines, Inc.
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 aviation oil is designed to suspend dirt and metal particles picked up from an aircraft 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. Aircraft engine oil should be changed every 25 operating hours when not using an oil filter.
Phillips 66, like other aviation oil manufacturers, recommends changing aviation oil every 25 hours if an oil filter is not being used. If an oil filter is being used, it should be changed every 50 hours.
4. Off-the-shelf oil additives do not improve aircraft engine performance.
Except in extremely rare instances, original engine manufacturers (OEMs) do not recommend using additives with aviation oil. Changing oil regularly is much more beneficial. Little is to be expected from the inclusion of aftermarket additives to an approved oil, and no OEM recommends their use. These include additives that claim to fortify or enhance the oil's lubrication properties.
5. Multiviscosity oils offer operating temperature benefits.
Multiviscosity oils such as Phillips 66 X/C 20W-50 oil offer high and low temperature protection for your engine. A 20W-50 oil acts like a 20W (winter) oil in cold engines and a 50-weight oil in hot engines.
The 20W provides instant lubrication and makes cold starting easier. The 50-weight protects against potential metal-to-metal wear during hot operation. Once an aircraft engine is started, it forgets how cold it is outside. It is only concerned with its high-heat operating environment. For this reason, engines require high-temperature lubrication even on cold days.
6. Fuel-injected engines can benefit from multiviscosity oil.
Proponents of fuel-injected engines claim they start better in cold weather than a carbureted engine. For this reason, a multiviscosity oil can be of great benefit to a fuel-injected engine because it can provide instant lubrication at cold start-up. Single-grade oil may not flow quickly enough to provide adequate lubrication at those low temperatures because it is too sluggish, creating excessive viscous drag.
Approximately 85 percent of harmful engine wear occurs during the startup phase.
7. 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 aircooled and operate under an entirely different set of parameters.
8. An oil's viscosity is key to its performance.
Viscosity plays a key role in preventing aircraft 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.
9. Using a multiviscosity oil can decrease oil consumption.
Phillips 66 has 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.
10. No detergents are ever added to aviation oils.
There is no such thing as an aviation oil that contains detergents. Aviation oils have not contained detergent packages since the mid 1950s. Single and multiviscosity grade mineral-based oils instead contain ashless dispersant (AD) additive packages. ADs are very different than detergents: ASHLESS refers to non-metallic additives. Detergents, on the other hand, are metallic by nature. Detergents may scrub existing ash deposits from an engine's interior surfaces, which will contribute to the ash content, and possible clogging, of the oil. . DISPERSANT refers to the oil's ability to suspend combustion byproducts, keeping them dispersed until the oil is drained. Because they suspend engine by-products, AD oils darken faster than non-AD oils. This is a sign that the oil is preventing by-products from solidifying on interior engine surfaces. All AD aviation oils contain oxidation inhibitors as part of their standard additive chemistry. AD oils will not dislodge quantities of sludge from interior engine surfaces that lead to restricted oil screens. AD oils do not add deposit build-up. Instead, they help dissipate existing by-products over time. For example, if an operator uses a non-AD oil for 500 hours, then switches to an oil with an AD package for 500 hours, the AD oil will not "clean out" the first 500 hours worth of engine deposits.
11. Engines using a straight mineral oil can easily be switched to an ashless dispersant (AD) oil.
If the changeover is completed properly, there are no negative effects to switching from a straight mineral to an AD oil, regardless of the number of operating hours accumulated. All AD aviation oils use the same base stock and additives. For instance, Phillips 66 Type A 100 Single Grade AD Oil uses the same base oil and additives as Phillips 66 multiviscosity 20W-50 X/C AD oil. AD oils will not remove past accumulations of lacquer and varnish or hardened sludge. Therefore, AD oils will not cause sludge to move, blocking oil galleys. When switching from mineral to AD oils, a darkening of the oil as the dispersant suspends surface deposits can be expected at the first two oil changes. This poses no danger to the engine and means the oil is properly suspending enginewear particles.
12. Aviation oil brands vary widely in performance.
All aviation oils provide some form of lubrication, but that's where the similarities end. Each manufacturer blends proprietary additives to enhance the oil and provide predictable performance characteristics for the end-user. Each oil's viscosity grade is designed to satisfy specific engine requirements. Using the right aviation oil for a specific aircraft engine can help improve engine efficiency.
13. 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 Phillips 66 20W-50 aviation oil 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.
14. Synthetic oils do not show superior performance when used in piston-powered aircraft.
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 aircraft 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 aircraft 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. Also, for piston-powered aircraft, any possible low temperature benefit to a synthetic oil is irrelevant because piston aircraft started in temperatures of 20F or below must be pre-heated. With regard to extremely high-temperature operation, very few, if any, piston powered aircraft are operated at temperatures that highlight the benefits of synthetic oils.
15. Using a multiviscosity AD mineral oil to break in a factory-new or zero-time overhauled aircraft engine will not damage the cylinders.
It is not true, as some believe, that multiviscosity mineral AD oils do not properly break in aircraft engines and 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.
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©2001 Southwest Regional Publishing, Inc.
(This information forwarded courtesy of Kori Ibey of Maximum North Aviation)