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Please refer to The AeroShell Book, Shelf life, periodic inspection and re-testing section (Edition 20, Page 36).

The validity of shelf life is based on the container remaining unopened, undamaged and stored under shelter at constant ambient temperature condition.

Once the product has been opened, there is no specified shelf-life period. This is because Shell has no control over the product's storage conditions, and therefore cannot guarantee the product's quality.

The answer is a definite no. When Shell first started evaluating multigrade aviation piston-engine oils over 25 years ago, testing proved that multigrades formulated only with mineral base oils did not have adequate base oil viscosity (thickness) to properly lubricate all high load points in the engine. Then we tested and flight evaluated a formulation made with all-synthetic base oils.

This formulation had excellent anti-wear characteristics in all tests run. However, in the flight evaluations, some engines would reach 600 to 900 hours, then lose oil consumption control and/or compression. When the engines were disassembled, we found that the piston rings were covered with a grey tacky substance that was primarily made up of the lead by-products of combustion (from the use of leaded aviation gasoline). Although synthetics are excellent lubricants with good high temperature stability and very good low temperature flow characteristics, they are relatively poor solvents.

In an aircraft engine, the lead by-products of combustion must be dissolved by the base oil so they can be carried away from the ring belt area and removed from the engine when the oil is changed. AeroShell Oil W 15W-50 is formulated with 50% synthetic base oils to give it the excellent low temperature flow needed for quick lubrication during cold starting. The synthetic base oils, along with the unique anti-wear additive system, provide effective anti-wear protection. In addition, its mineral base oils provide lead absorbency to guard against ring sticking and excessive sludge. The bottom line: The synthetic component of AeroShell Oil W 15W-50 will not harm your engine. Instead, it gives you the best of both oils

Frequent and consistent oil change intervals are one of the most critical factors in promoting engine health and longevity. But, in addition to oil change intervals, it is just as important how you change it.

Engine overhaul shops typically recommend changing both the oil and filter every 25 hours. Some operators prefer to change the oil at 25 hours and the oil filter every 50 hours. While this method is within the original manufacturer鈥檚 recommendation, consideration should be given as the primary purpose for changing oil is to remove contaminants. If you do not change the oil filter each time, the new oil will automatically start off with one quart of contaminated used oil. Secondly, oil filter inspection is probably the single most important tool for monitoring the health of a piston engine. So, when the oil filter is changed, it should always be cut open and inspected.

Low usage aircraft should have their oil changed every four months. When an aircraft engine sits idle, the used oil in the engine can be quite acidic which, when combined with water from the atmosphere, causes corrosion. This problem is then compounded when the rust particles that are formed, get into the oil and act like a grinding paste when the engine is next started, causing further wear and damage. By changing the oil more frequently, you reduce the chances of corrosion occurring resulting in a significantly less abrasive oil in the engine.

Finally, and maybe most critically, very close attention should be paid to oil pressure coming up within 15-20 seconds on the initial start-up after the oil change. Attention should always be paid to oil pressure coming up at every engine start, but especially following an oil and filter change. Aircraft piston engines are subject to oil pressure anomalies, primarily loss of prime at the oil pump.

This condition is likely to occur during an oil change. Pre-oiling with a pressure pot is highly recommended. Turning the engine through with the starter (with spark plugs removed) is also an acceptable method but use extreme caution around the moving propeller.

If oil pressure is not established in the first 15-20 seconds, abort the start. Do not attempt another start until the problem is found and corrected. Running an engine without oil pressure, even for a brief period will destroy any benefits of even the most frequent oil change intervals.

The compatibility question covers two considerations:

Mixing one grade of AeroShell PEO with another:

All approved SAE J-1899 (former MIL-L-22851) and SAE J-1966 (former MIL-L-6082) AeroShell piston engine oils are compatible and can be mixed with each other.

The effects on the engine of changing from one AeroShell PEO grade to the other.

If you typically run on AeroShell W 15W-50, and you find yourself in a place where only single grade AeroShell PEOs are available, you can safely add the single grade AeroShell PEO to your engine. They are completely compatible.

If you run on a single grade AeroShell PEO during the summer but want to switch over to AeroShell Oil W 15W-50 (multigrade) for the winter, you can safely replace the single grade with the multigrade at your regular drain interval. The idea that you have to stick with the type of oil you started with comes from the days of unusual chemistry when the resulting oils were incompatible.

If you have a high-time engine running on ashless dispersant oils and need to replace a cylinder, you can switch to a mineral oil for 50 hours or so to break in the new cylinder. The only time Shell recommends against switching is in a high-time engine run exclusively on straight (non-ashless dispersant) mineral oil. Here, a switch to ashless dispersant oil can loosen deposits left behind by the straight mineral oil.

Can AeroShell Oil W100 Plus/ AeroShell Oil W 15W-50 be used for a 鈥渟hort storage鈥�? If yes, up to how many months?

What is the maximum storage period with AeroShell Fluid 2XN?

It is important that an aircraft be properly prepared if it is going to be inactive for a protracted length of time. This extends to the oil you use.

When an aircraft sits unused, especially in humid conditions, it rusts. Rust forms in the engine on cams, lifters and cylinder bores. Rusting can cause pitting, and the rust particles may act as a very fine grinding compound in your oil. This can lead to increased wear and reduced engine life.

If your plane is going to be stored for the winter or if you are in the middle of a major restoration or repair project, it makes sense to use a special preservative such as AeroShell Fluid 2XN. AeroShell Fluid 2XN can be used without blending for long-term engine inhibition or blended in the ratio of one part of AeroShell Fluid 2XN to three parts of fresh AeroShell straight mineral (break-in) oil (80, 100, 120) to be used as an inhibited flyaway oil. (When using AeroShell Fluid 2XN in radial engines, you cannot use the product as flyaway oil; it should only be used for ground running.) This resulting mix is excellent for use in engines that are going to be inactive for several months, as is often the case over winter. This blend of AeroShell Fluid 2XN and AeroShell straight mineral (break-in) oil can be used in any certified aviation engine, although it is not recommended for use in two-stroke or automotive-derived engines.

Using AeroShell Fluid 2XN is easy. Once the AeroShell Fluid 2XN has been mixed with AeroShell straight mineral oil, the normal operational oil can be drained and replaced with this blend. You should run the engine for about 15 minutes, either on the ground or in the air, to circulate the oil then shut the engine down and follow the normal storage procedure. For additional protection, this oil can also be sprayed into the cylinders and other areas. Once the engine has cooled, it is worth blocking off the intake and exhaust, if possible, to reduce the flow of air (and therefore moisture) through the engine. However, you should remember to placard the cockpit to remind yourself and other pilots that this has been done.

Once you are ready to change back to your normal oil, you must first run the engine (for radial engines, only ground run). Run the engine to its normal operating temperature, then let the engine and oil cool down to a temperature that is safe to proceed with the oil change. Next, drain the preservation oil and refill the engine with the correct grade of AeroShell piston engine oil. Many operators with low-utilisation aircraft are taking advantage of the anti-wear and anticorrosion additives found in AeroShell Oil W 15W-50 multigrade and AeroShell Oil W Plus products. They often ask whether to use dedicated inhibiting oil such as AeroShell Fluid 2XN and the answer lies in the utilisation of their aircraft. If you intend to carry on flying throughout the year, but may have a few periods of several weeks鈥� inactivity, you should use AeroShell Oil W 15W-50, AeroShell Oil W100 Plus or AeroShell Oil W80 Plus. However, if you intend to lay the aircraft up for several months (winter or summer) and perhaps enjoy the occasional flight during this period, you should use AeroShell Fluid 2XN mixed with AeroShell straight mineral (break-in) oil. The engine can only be flown for a maximum of two hours when using AeroShell Fluid 2XN per storage, and a total of 50 hours over the life of the engine when using AeroShell Fluid 2XN.

By definition, AeroShell Oil W 100 (single grade) and AeroShell Oil W 15W-50 (multigrade) both meet the same specification. At normal operating temperatures (about 200掳F, 93掳C), both oils will have the same thickness or viscosity. In a perfect world, with perfect flying conditions and weather, both oils would provide excellent service in an aircraft flown at least once a week.

However, in reality, things are rarely perfect. Under normal conditions, AeroShell Oil W 15W-50 does a lot of things better than a single grade:

The biggest advantage for AeroShell Oil W 15W-50 is in cold weather starting. AeroShell Oil W100 is up to 10 times thicker at cold temperatures than AeroShell Oil W 15W-50. The improved low temperature flow characteristics improve cranking, and more importantly, speed the oil to the bearing surfaces faster once the plane has been started.

Another major difference is that AeroShell Oil W 15W-50, AeroShell Oil W100 Plus and AeroShell Oil W80 Plus contain the LW 16702 anti-wear additive that is not found in AeroShell Oil W100. This additive, along with the semi-synthetic base oils, helps to reduce friction and improve flow in AeroShell Oil W 15W-50. These additives improve lubrication and reduce oil consumption past the oil rings. Conversely, the improved flow can increase oil loss through leaks or loose intake valve guides. Therefore, your oil consumption may go up or down if you switch from AeroShell庐 Oil W 100 to AeroShell庐 Oil W 15W-50.

The improved flow and reduced friction characteristics of AeroShell庐 Oil W 15W-50 will also help to reduce oil temperatures unlike using AeroShell庐 Oil W 100. This is particularly important in engines that run hot, such as turbocharged, high-performance or aerobatic aircraft engines. Pilots should always remember to monitor the oil temperatures to ensure that they are not too high. In cold weather, you should also make sure that the engine temperature is high enough to boil off the water that naturally accumulates in the crankcase. Temperatures in the 180鈥�200掳F (82鈥�93掳C) range are recommended for most applications.  AeroShell Oil W 15W-50 Multigrade also provides vastly improved resistance to oil cooler plugging on extremely cold, high-altitude flights.

With that said, is AeroShell W 15W-50 always a better choice than AeroShell Oil W single grades? The answer is, not necessarily. Single grade oils have their place; it is just a matter of knowing when and why to use which oil.

In summary, HPC oils will have:

• very low coking propensity (in both liquid phase and vapour/oil mist phase)
• higher oxidative stability
• higher thermal stability
• improved compatibility with a wide range of elastomers
• better defined load-carrying capacity

Oil separation, or oil bleed as it is commonly referred to, is the result of many contributing factors. AeroShell greases are made up of thickening agents (such as clay or lithium complex soaps), grease additives, and lubricating oil. All of these components are very carefully blended to provide desirable grease lubricating properties. However, of all the components that make up a grease formulation, it is the lubricating oil that is actually providing the lubrication. A calculated amount of oil bleed is required at all temperature ranges for the grease to be effective.

For example, a grease like AeroShell Grease 33 that is certified for use from 鈥�73掳C to +149掳C must have acceptable oil-bleed rates at both temperature extremes to provide proper lubrication and protection of the intended part. Greases typically exhibit more oil separation the warmer the ambient temperature, which is why this phenomenon is more apparent during the warmer months of the year.

Another factor that has a direct effect on oil-bleed rate is the amount of grease used. Often excessive amounts of grease are used in an effort to expel contaminants from the component being serviced. The excessive purged or vented grease left in a static state around the component should be removed to avoid oil drops forming in these locations.

The general industry theory is that the proper amount of grease is approximately one-third of the open volume of the unit being serviced. That said, there are a large number of variables to consider when determining how much grease to use.

First and foremost, we would advise consulting the appropriate aircraft or component maintenance manuals or service bulletins for specific advice on not only the correct grade of grease to use, but also on the proper method of application. Many aircraft components specify the purge method of grease application.

Purging is the process of injecting grease into the grease fitting until all of the old grease has been pumped out and replaced by the new grease. This method is often utilised in cases where it is necessary to expel contaminants such as wear debris, dirt, and water on a periodic basis. When using the purge method, it is important that excess grease be removed after servicing as it will attract dirt and hold debris, making future service intervals more difficult to accomplish.

Care should be taken in applications where open venting of excess grease is not one of the design characteristics of the unit being greased. In these cases, adherence to the recommended amount of grease to use per the maintenance manual is critical.

Another thing to watch out for is over-greasing of some closed systems. This can have a negative impact on seal longevity and may cause the unit to operate at a slightly elevated temperature initially after servicing.

What is grease incompatibility? The National Lubricating Grease Institute (NLGI) definition states that two greases show incompatibility when a mixture of the products shows physical properties or service performance which are markedly inferior to those of either of the greases before mixing. Performance or properties inferior to one of the products and superior to the other may be due to simple mixing and would not be considered as evidence of incompatibility; this is sometimes referred to as "performance dilution".

In general, mixing of greases made with different thickener types should be avoided; thus clay thickened greases should not be mixed with soap thickened (e.g. lithium complex) greases as this can lead to breakdown of the thickener structure. Incompatibility between greases can also arise from additive interactions.

In some cases, different greases approved to the same specification may be incompatible with each other; to account for this, the MIL-PRF-23827C specification was amended to divide approved greases into Type I (soap-based) and Type II (clay-based).