Aircraft engines are built to be used on a regular basis, so any length of inactivity must be met with proper maintenance planning to ensure the engine remains in proper working order. Although experts recommend taking a plane up at least once a week for 30 minutes to an hour to prevent engine problems, many pilots in today's economy have been forced to significantly reduce flight time due to tightened budgets and increased operating costs.

Basic Principles
Rust does happen. In some cases it will form because the engines aren't flown long enough to evaporate the water generated from condensation or blow-by from the combustion process. However, rust generated in this manner is the exception, rather than the rule. The most common cause for rust is improper aircraft storage. There are several different ways to help prevent rust and pilots must be familiar with these tactics if they plan to store an aircraft for longer than a few weeks. Whatever the type of operation or reason for storing an aircraft, there are several principles that should be followed to ensure your investment is adequately protected based on one of the following operating conditions:

• Frequently flown: If your plane is flown several times a month, for periods longer than one hour, there is little, if any, need for additional rust protection. Our decades of experience indicate the existing rust-inhibiting properties of our ashless dispersant conventional oils perform very well for preventing rust in this type of service.
• Infrequently flown: We define an infrequently flown plane as one that sits for several weeks to a month or more. We recommend that if you're more than halfway through the normal engine oil drain interval, change the oil and fly the plane to circulate the fresh oil through all the bearings and valve train. Parking the plane with fresh oil will greatly reduce the likelihood of any bearing corrosion that may result from contaminated or acidic used oil.
• Infrequently flown with significant intervals (such as winter months) of non use: The use of a preservative oil, such as Phillips 66 Aviation Antirust Oil can significantly improve protection against rust when used as a top-off with conventional aviation piston engine oil. We recommend adding 10% of Aviation Antirust Oil 20W-50 to the engine oil and flying it for 30 - 60 minutes to allow good distribution of the antirust additive before parking the plane.
• Long-term storage: More than three months of continuous storage and the engine should be treated to a full change of preservative, or "pickling" oil, such as our Aviation Antirust Oil. Drain the crankcase and refill with straight Antirust Oil then fly the plane for at least an hour and park it taking all other steps for long periods of storage such as covering the exhaust. No matter where a plane is stored, critters and insects can pose just as big a threat to aircraft parts as rust and corrosion. Wasps and small birds are notorious for building nests within exposed areas of the exhaust and exhaust valves. When these nests go unnoticed by pilots or the maintenance staff, they can be ingested when the engine is powered up, resulting in significant damage to critical engine parts and also jeopardizing the safety of those onboard. During extended storage periods, every opening on the aircraft's exterior should be carefully sealed to ensure nothing can fly or crawl into the plane. Additionally, when preparing a stored aircraft for flight, checking for such nests is a crucial step prior to operation.

Summary
Regardless of the reasons for a plane being stored, always plan ahead so that no step of the process is missed, and overestimate the anticipated storage time period in the event the aircraft needs to sit longer. While there are many components to proper aircraft storage, the process is easily manageable when broken down in a few simple steps and is critical to the long-term health of an airplane engine.

There are no lubricants designed to remove rust and the writer doesn't indicate where the rust was found or what type of metallurgy is involved. However, generally when talking about rust, steel is involved. Unlike nickel- and chrome-plated cylinders, many steel cylinders will get a rusty haze on the cylinder wall while the engine is at rest for a few days or more. This type of rust typically isn't very destructive and, between the action of the piston rings and the combustion process, this rust haze is burned off or otherwise removed shortly after start up. If the rust is more severe than a haze and the process is frequently repeated over time, the cylinder cross-hatch may be polished off and oil consumption may become excessive. Also, if the rust observed by the borescope is substantial and pitting appears to have formed on the cylinder walls (usually at the lowest point of the cylinder) then disassembly is likely called for. If you use a borescope in the crankcase by going through the oil drain hole and rust is found on the cam lobe or lifter face, then I recommend you get the opinion of an experienced mechanic to determine the severity and get his opinion on the need for repairs. It isn't uncommon for lifters to run through TBO with some surface pits so experience with such conditions can save significant dollars in repair cost. Incidental rust on connecting rods or crankshaft throws usually do not result in failure or significant damage. However, it is an indication that rust is forming and steps such as the use of an antirust oil should be taken to arrest the rusting process.

The proven advantage of multigrade oils is that they result in faster lubrication at start up (when most wear occurs) they exhibit better high-temperature protection in the piston ring belt area, and provide significantly cleaner engine operation than comparable straight-grade oils.

Simply defined, "viscosity" is the measure of a fluid's resistance to flow and viscosity is one of the most important characteristics to consider when selecting aviation oil. However, the different viscosities of today's aviation oils aren't always universally understood. Understanding the science behind multigrade aviation oil as well as the key features and benefits of these products will help you better manage your engine's performance and will increase your proficiency in overall airplane piston engine maintenance.

A Brief History
The use of multiviscosity oils has evolved over the years and has gradually become the norm for virtually all mobile equipment applications, such as automotive, trucking, heavy duty off-road equipment, railroad and many others. In the beginning there were only monograde oils. As aircraft engines evolved, maintenance experts began seeking oils with superior cold temperature properties and enhanced high temperature protection. Through the use of polymers, scientists have been able to improve the cold temperature start up capabilities of oils while simultaneously achieving enhanced protection in high temperature climates.

How Multiviscosity Oils Work
The first multiviscosity aviation oil, Phillips 66 X/C, was introduced in 1979 but, even today, few people understand its unique performance benefits. After all, how can a multiviscosity aviation oil flow smoothly at low temperatures while properly protecting the engine at high operating temperatures? Multigrade oils are composed of a small amount of polymer, which is a chemical component that imparts good high temperature protection, blended with a variety of base oils that have very good low temperature properties. This blended polymer, also known as a Viscosity Index Improver, provides resistance to oil thinning as temperatures increase by expanding as it gets hotter. For example, in the case of a 20W-50 fluid, the oil flows like an SAE 20W at start up, but retains the properties of an SAE 50 at 100° C. Due to the use of these VII's, multiviscosity oils actually maintain their film strength and viscosity in elevated temperatures better than straight grade oils.

The Benefits of Multiviscosity Oils
In extremely cold conditions, it used to be a common practice to drain an airplane's engine of all its oil while it was still hot. Then, the oil was moved inside to maintain a warm enough temperature that would allow for continued flow of the straight grade oil at the next start up. This practice continues today in the most extreme situations. However, thanks to today's multigrade oils, it is more common for the oil to remain in the engine year-round. In comparison to straight grade oils, which are only required to satisfy the 100° C specifications, multigrade oils service have to meet both high and low temperature requirements (see the SAE Viscosity Grade Chart below). The "W" rating, which stands for "winter", of the low number in the viscosity grade indicates that the oil has met the requirements of several low-temperature tests measuring both cold flow and cold cranking ability. The smaller the number that precedes the "W", the lower the temperature at which it was tested. A cold start is generally defined as being one that occurs below 60° F. However, the reality is that it's always a cold start to your engine. Even when the ambient temperature is warm, it just doesn't compare to the normal operating temperature in the engine once it warms up. This capability to perform well at all temperatures is extremely beneficial for pilots in every region of the U.S. as well as traditionally warm international climates such as those in the tropics.

The improved cold temperature flow characteristics of these oils allows for the ease of distribution throughout the engine, reducing start up oil pressure spikes (resulting in longer life from oil coolers), less strain on the starter and dramatically improving flow to critical engine components at start up. Due to the formulation of multigrades as compared to straight grade oil, consumed or burned multigrade oil leaves fewer deposits on the pistons and combustion chambers. Typically a pilot will see cleaner crankcase and exhaust systems after switching to multiviscosity oil.

Making the Switch
Some pilots argue that the change to multigrade is unnecessary because they may not fully appreciate the numerous benefits. Using the appropriate multigrade oil year-round can help airplane owners avoid the hassle and potential for human error associated with adjusting aviation engine oil seasonally. There are many advantages to using multiviscosity oil − starting from the time you fire up your plane until you park it in the hangar. So whether you live in Alaska or Florida or are operating a radial or opposed piston engine, multigrade oil will keep your airplane running smoothly and efficiently from day one.

Full synthetics and synthetic blend motor oils are marketed heavily for use in automotive applications because of their ability to provide better performance at very low temperatures (often with 0W- or 5W- viscosities) and better oxidation stability at prolonged high temperatures in support of longer drain intervals promoted by automotive OEM's. It is our opinion that the advantages which make synthetic and synthetic blend engine oils so attractive in automotive and trucking applications, rarely apply to the needs of aviation piston engines using leaded fuel or specifying a SAE J1899 engine oil.

Mineral-based multiviscosity oils provide excellent cold-cranking and cold flow characteristics in line with what one might expect from a synthetic. On the other end of the temperature spectrum, most aviation piston engines operate in the 190 – 210°F range, well below the capability of the oil. An additional important distinction to make between automotive and aviation applications is that aviation piston engines are serviced, rightfully so, at very short intervals which eliminates the need for extended drains sometimes associated with synthetic oils.

Synthetic oil is incapable of solubilizing engine contamination and combustion by-products (synthetic blends provide better solubility than full synthetics because they are mixed with mineral base oils) in aviation engines that run on 100LL fuel. Mineral-based formulations provide the best natural solubility characteristics which is why they tend to run cleaner than their synthetic blend counterparts.

For many pilots, it boils down to a simple economic evaluation that mineral formulations provide everything their engine requires without the unnecessary added cost and unrealized benefits of a synthetic or synthetic blend.

A persistent perception in the aviation community is that monograde, commonly referred to as straight-grade, aviation piston engine oils adhere to engine parts better than their multigrade counterparts, thus providing better protection during periods of inactivity. While it may make initial intuitive sense that a thicker straight-grade oil would remain on engine components longer than a multigrade oil, the simple fact is that all aviation engine oils drain off the parts down to a residual oil film thickness of three to four microns (25 microns = 1/1,000 of an inch) after just a few hours – regardless of the brand or viscosity of the aviation engine oil tested. So the idea that one achieves greater oil retention with single grade oils is a busted myth.

To answer the question on whether there is any oil and/or how much oil is left on engine parts after the engine is shut off, we tested for oil retention in the laboratory to measure the amount of oils retained on a surface over time. The study explored oil retention for both multigrade and monograde aviation piston engine oils.

The oil retention test was performed by measuring the mass of oil retained on the surface of a steel coupon which was suspended from a highly sensitive balance. The steel coupon was dipped into the test oil which was heated to 200°F and then cooled down to room temperature to mimic the situation in aviation engines when the engine is shut down at a higher temperature and then cools down to ambient temperature for idling or inactivity. The total weight of the steel coupon plus the amount of oil retained on the test piece was recorded every 2 hours for 48 hours total. Test results showed that after the parts rested for 12 hours, very little of the original oil film remained on the surface and the rest flowed back to the reservoir regardless of the viscosity and initial temperature of the oils tested. In fact, the oil drains very quickly within the first 2 hours, and then slows down significantly over time leaving less than 8% in mass and 2um in oil film thickness (as measured by FTIR) on the surface after just 20 hours.

Lycoming has three engines in varying configurations that require the Lycoming additive LW-16702 or equivalent. These engines have cam lobe and lifter design features that require additional scuff protection above and beyond the other Lycoming engine models. Below is the list of engines that we found in the Lycoming literature that requires the LW-16702 or equivalent additive as found in Phillips 66 Type A 100AW.

• O-320H
• O-360E
• LO-360E
• TO-360E
• LTO-360E
• TIO-541
• TIGO-541

A dispersant is an ashless (non-metallic) engine oil additive that helps prevent sludge, varnish and other engine deposits by breaking up insoluble contaminant particles. These microscopic particles are kept suspended (or "dispersed") in the oil so they can be carried to the oil filter or until the oil is drained when no filter is installed. Ashless dispersants do not create hard deposits when burned.

A detergent is a cleanliness additive made of metallic compounds to protect from sludge and varnish build-ups. However, these metallic compounds can form harmful deposits when burned and those hard deposits could lead to pre-ignition problems in aviation piston engines. For this reason, detergents are not allowed in aviation piston engine oils qualified under SAE J-1899 (obsolete MIL-L-22851) or SAE J-1966 (obsolete MIL-L-6082). No current aviation piston engine oil meeting the SAE J-1899 specification contains detergent compounds.

* Some aviation applications using diesel engines, Rotax engines or some other specialized power plant may require different engine oil formulations.

Please do not use an automotive engine oil in your aviation engine that calls for a product meeting the SAE J1899 (formerly MIL-L-22851) standard. The design and testing of automotive engine oils does not take into consideration their use in any other application other than automobile engines. A very important issue is that automotive oils all contain chemistry that, when burned, often produces hard combustion chamber deposits which could lead to pre-ignition. This is not an issue in automotive engines because they consume much less volume of oil in any given operating time frame. If you used a quart of oil every four hours in your car, you would be ready to rebuild the engine. The designs, normal operating environment, fuel consumed and requirements of automotive and aviation piston engines are very different and their engine oil needs are just as unique.