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Find answers to the most commonly asked questions about ExxonMobil Aviation products and services.

For additional information, or to make specific inquiries, please contact your ExxonMobil Aviation representative or submit an inquiry online.

General questions

Here is a brief list of common industry terminology:


Auxiliary Power Unit


Constant Speed Drive


Integrated Drive Generator


Bypass Ratio


Time Between Overhaul


Mean Time Between Failures


Mean Time Between Removals


Specific Fuel Consumption


Exhaust Gas Temperature


Extended Twin-engine Operations


In-flight Shutdown

Dates defined:

− Date Printed represents the date the certificate of oil analysis was printed

− Plant Dispatch Date represents the fill date; this is the date the product was actually packaged/filled in its container

− Date of Manufacture represents the certification date, or testing date

The shelf life on an aviation lubricant product is listed on the container/package as the “Use by” date. In the event that the package/container does not have a “Use by” date, check the manufacturing date list in the Certificate of Analysis (COA) and add the recommended shelf life. For information on recommended shelf life, please refer to the COA (shelf life referenced on bottom of the page), or the ExxonMobil Aviation Shelf Life Bulletin.

Jet turbine oils

Jet oils are lubricants developed specifically for aviation gas turbine engines. Jet oils are designed to operate over an extreme temperature range. Temperatures can range from -40 degrees Celsius for cold starting at high altitudes and go up to 250 C for bearing lubrication. Jet oils can also be used to lubricate certain land-based and marine engines (aviation derivatives) typically used for power generation or propulsion aboard seagoing vessels.

Many airlines prefer quart cans. Quart cans provide for ease in handling when performing reservoir "top-offs" during maintenance checks. Additionally, quart cans have a longer shelf life as a result of hermetic sealing. Jet oils are extremely hygroscopic due to their chemical composition; they can attract/pick up moisture from the air easily, even past the bungholes on pails and drums, due to expansion and contraction associated with temperature swings. Once a quart can is opened it is difficult to reseal, and as such, should be used entirely or disposed of. Reusing open quart cans increases risk associated with collection of moisture and/or other potential contaminants (e.g., dust, dirt, etc.), therefore it is recommended for single use application only.

The shelf life for all Mobil Jet oils in metal quarts is 10 years, and five years for all products in pails or drums. We recommend effective inventory management be employed to ensure the stock of Mobil Jet oils is rotated for storage and use.

With regard to handling, please refer to the Material Safety Data Sheet (MSDS). Generally no special precautions are necessary beyond standard good hygiene practices. In addition, there is no need to shake, stir or otherwise agitate the oil before use. The ester base oils used in Mobil Jet™ Oil II and Mobil Jet™ Oil 254 gas turbine lubricants have excellent additive compatibility and long-term storage stability characteristics.

A certificate of compliance is a document similar to what's commonly referred to as a Certificate of Analysis (COA). COAs are filed for every batch of Mobil Jet oil produced. A COA can be obtained by contacting your ExxonMobil source point or downloading a copy from our website.

Gas turbine oil coloring is determined by the additive package selected and can vary between oils. It is not an indicator of oil quality or suitability.

Yes, they are compatible. The oil approval process includes compatibility testing for all jet oils. Approval requirements mandate that jet oils must have full capability in any proportion with any other similarly certified oil. The US Military also requires that qualified oils be compatible with other oils that meet the same specification.

First, always consult with the engine/equipment builder recommendations prior to enacting the changeover to ensure compliance. Next, we recommend converting systems by simply "topping-off" the system with the new oil. This approach allows the original brand of oil to be phased out gradually over time as more "top-offs" occur. The standard "drain and fill" method is less desirable because there is the potential for disturbing system equilibrium (e.g., seal swell/compatibility, deposit loosening/washing, etc). Since oil is consumed in a jet engine on a regular basis (average - 0.20-0.80 quarts/hr), estimates indicate the oil system will typically contain more than 95 percent of the new oil in a few hundred hours of operation.

The biggest difference is that land based installations do not have the benefit of ram air cooling and therefore the reservoirs typically are larger (500+ gallons versus 6 gallons) in order to provide sufficient residence time for oil cooling. Additionally, many land-based turbines are run intermittently for peak electrical or gas compression periods, as opposed to every day as in the case of aircraft engines. All of this results in the potential for a higher possibility of acid formation due to buildup of moisture/water in the lubricant. As such, many equipment manufactures recommend reservoir drain and flush service intervals to ensure continued oil performance. It should be noted that while the larger reservoir systems provide for oil cooling, the internal engine temperatures are every bit as severe as those seen in an aircraft engine. Therefore the need for good thermal stability is still a critical performance feature of synthetic jet turbine lubricants used in land-based applications.

Mobil Jet oils are compatible with the materials provided under normal conditions of jet engine operation. For compounds and components (e.g., plastics) not typically used in aviation engines, compatibility studies must be run. Even with elastomers, great care must be exercised when applying data from one study to another. Unique circumstances could result in a response that is different from that predicted in a study. Elastomers, like lubricants, have many and varied formulations, all of which may not react in a similar fashion under the same conditions. Consequently, each situation/application must be evaluated separately.

Mobil Jet oils have a safe history of use in both ground and air operations for more than 50 years. ExxonMobil is not aware of any adverse long-term health effects associated with aircraft use of jet engine oils. Refer to the MSDS (Material Safety Data Sheets) for additional handling and safety information.

Hydraulic fluids

Hydraulic systems use a confined fluid to transmit power. The fluid used to transmit power is called a hydraulic fluid, or oil, and also functions to cool and lubricate the hydraulic system. Aviation hydraulic systems fulfill various functions, including moving flight control surfaces that help steer, take off and land aircraft. Hydraulic fluids help to engage aircraft brakes and deploy or retract landing gear.

Exxon HyJet IV-Aplus and Exxon HyJet V are fire-resistant hydraulic oils while other 5606 fluids are not considered fire-resistant. Fire-resistant fluids have evolved over time as commercial jet travel has become more prevalent. Fire-resistant fluids were developed to accommodate increased aircraft speeds during landing and withstand higher braking temperatures. Fire resistance properties of these oils include high auto-ignition temperature and zero flame propagation. Additionally, the oils must meet special OEM test requirements such as hot manifold ignition and high- and low-pressure spray tests, among others.

Fire-resistant hydraulic oils are dyed purple to differentiate them from 5606 fluids, which are red in color.

In addition to normal housekeeping requirements used to minimize contamination, you should also minimize any periods of exposure of the product to air by keeping containers closed for storage. HyJet products will rapidly absorb moisture from the air, which will lead to hydrolysis – a chemical degradation of the product. Previously opened containers with low fluid content should therefore not be stored for long periods of time.

Long-term exposure to HyJet products can cause irritation and dry skin. These fluids will also be painful if they come in contact with the eye, although there is no evidence of long-term harm to the eye. Accordingly, proper personal protective equipment should be used when handling HyJet products.

Proper handling of HyJet products is well documented in the MSDS.

The shelf life of HyJet IV-Aplus and HyJet V hydraulic fluids is 10 years for quarts and gallons, and five years in pails and drums. The date of manufacture can be determined using the batch and fill codes printed on each package.

HyJet products are fully compatible in any proportion with each other and with other commercially available phosphate ester based hydraulic fluids. Additionally, aircraft OEM require a multitude of compatibility tests, including compatibility tests with metals, elastomers, solvents and paints. Please contact your ExxonMobil aviation representative for specific compatibility inquiries.

Conversion is typically completed using the “top-off” method in which HyJet products are added to hydraulic reservoirs as required to maintain proper fluid levels. Using this method, the original fluid will gradually be phased out as more “top-offs” occur. Please contact your ExxonMobil aviation representative for specific conversion suggestions.

Yes, ExxonMobil aviation offers Exxcare as a routine in-service fluid analysis program for HyJet customers.

HyJet V hydraulic fluid offers extended fluid life over HyJet IV-Aplus without sacrificing fluid performance in preventing wear, rust and deposits or increasing weight. HyJet V hydraulic fluid is also certified for use in 5,000 psi hydraulic systems.

Piston engine oils

Semi-synthetic is a term that indicates that the oil is a blend of synthetic and mineral-based oils (plus additives). A semi-synthetic oil takes advantage of the oxidative stability, high-temperature performance and excellent lubricating properties of synthetic oils without sacrificing the natural solvency provided by mineral oil.

A multigrade oil is formulated to meet the viscosity-grading requirements of more than one SAE grade. Multigrade oils use polymeric additives that give the oil the flexibility to lubricate effectively over a wider temperature range than monograde oils.

Compared to a monograde oil, a multigrade oil will provide better cold-start protection and a stronger lubricant film at typical operating temperatures. Other benefits include lower oil consumption and better fuel economy. Multigrades are also more versatile, since they do not need to be changed seasonally.

Yes. Exxon Elite oil has a proprietary formulation. While the Exxon Elite formulation was developed in the mid-1990s, the formulation has been refined and additive package subjected to rigorous testing.

ExxonMobil engineers determined that fully synthetic oils may not have the solvency needed to handle the lead deposits resulting from the use of leaded fuel. So they developed a semi-synthetic formulation – Exxon Elite – that combines the best of both synthetics and conventional oils without sacrificing solvency characteristics. Exxon Elite oil also has a highly effective dispersant that will provide excellent deposit control.

There are many compelling reasons for all aircraft owners to try it. Exxon Elite oil can provide advantages over virtually all other commercial aviation oils currently on the market. Some consumers may find that Exxon Elite oil gives them better wear and corrosion control versus their current lubricant. Others may find better rust protection. Still others may find that Exxon Elite oil is better in all of these categories.

Yes. Exxon Elite is an SAE J1899 certified oil. That means it meets the requirements of engine OEMs and the US Military for ashless dispersant-containing oils. It meets MIL-L-22851D (obsolete) and is US Military approved.

Exxon Elite oil also has FAA Supplemental Type Certificates for Lycoming and Continental engines. The FAA has further approved Exxon Elite oil as an Alternate Method of Compliance with Airworthiness Directive 80-04-03-R2, paragraph b.1, which requires the use of an antiwear/anti-scuffing additive in some Lycoming engines. The FAA has issued a Special Airworthiness Information Bulletin stating this fact: SAIB No. NE-00-22.

The antiwear/anti-scuffing additive (sometimes referred to by the Lycoming stock number LW 16702) is a supplemental additive required in some Lycoming engines. This additive deters scuffing on the engine models in question, particularly during engine starts. The FAA has required its use in those engine models affected by Airworthiness Directive 80-04-03-R2, paragraph b.1.

Exxon Elite oil contains one of the two additives approved for this usage. Using an oil that already contains this additive results in a more consistent concentration of the additive throughout the drain interval. It should provide better protection against scuffing and wear than oils that do not contain the additive.

No. Regardless of the oil you are using, OEMs and the FAA require that standard oil drain intervals be maintained. That will not change with the introduction of Exxon Elite oil.

Yes you can, but you will not reap the full benefits of Exxon Elite if you mix it with other oils. In order to gain SAE J1899 certification, a lubricant must undergo compatibility testing that proves that it is compatible in any proportion with any other similarly certified oil. Accordingly, Exxon Elite is compatible with any certified ashless dispersant oil, including both monograde and multigrade oils. It is also compatible with break-in oils (SAE J1966) and can be used immediately following break-in.

While supplemental additives will probably do no harm, their use is not recommended. With the exception of the antiwear/anti-scuffing additives required for some Lycoming engines, the claims made by manufacturers of supplemental additives are typically hard to prove or disprove.
Exxon Elite oil contains a proprietary formulation that carefully balances the properties of its base oils with the properties of its additives to ensure that the oil provides the protection you need, lasts long enough to get you to your next drain interval and is fully compatible with other certified products. Supplemental additives are typically an unnecessary added cost.

There are a wide variety of factors that affect whether your engine makes it to TBO or even beyond TBO. According to ExxonMobil engineering tests, Exxon Elite oil's formulation provides excellent protection against wear, corrosion and rust.
Exxon Elite oil can be used in any application requiring an SAE J1899 or MIL-L-22851D (obsolete) oil. Typically, the oil specification you need is determined by engine model and not by aircraft model. Therefore, ExxonMobil always recommends checking your engine operating manual for information on oil requirements.
No. Exxon Elite oil requires no special filtration.
Significant progress has been made over the years in extending TBOs from about 1,200 hours to the 2,000-hour specification. This progress, however, did not occur as the result of changes in any single engine component or engine lubricant. The broad acceptance of ashless dispersant oils has certainly helped extend TBOs, but overall progress has been achieved through a variety of innovations. Any continued extension of TBOs, if it occurs, will likely be achieved in the same manner, and not just via a better oil.

This white, milky substance is an emulsion formed on the surface of the fluid or an oil-wetted part and indicates the presence of minute amounts of water mixed with oil. It is probably harmless. To be sure, you need to make sure you do not have water in your oil. You can do this by asking your oil analysis lab to test a sample of your oil for water (If you are not analyzing your oil, we can send you a test kit). If the lab indicates you have water in your oil, replace the oil with fresh oil.

If the lab indicates that your oil does NOT contain water, then the emulsion you are seeing is harmless and is the result of condensate in at least this part of the engine.

This kind of phenomenon has been observed in engine oils that contain potent dispersants and rust inhibitors, as present in Exxon Aviation Oil Elite 20W-50 engine oil. Condensation can occur even when an engine is stored in a warehouse, or where humidity is relatively low. One of the products of combustion is water vapor. Hot air around the engine may be saturated with water. As the engine cools, water can condense onto cool surfaces. While any water in the engine has probably boiled off, small amounts of condensation may collect around the fill cap and mix with oil droplets to form a creamy emulsion.

Exxon Aviation Oil Elite 20W-50 oil will do its job in protecting against rust from this type of moisture.

Because of the wide variety of additives used in a modern engine oil like Exxon Aviation Oil Elite 20W-50 and the manner in which these additives behave in your engine, oil color is not a very reliable way to determine oil quality.

Impurities are created in your engine as a by-product of combustion. Exxon Aviation Oil Elite 20W-50 oil is formulated with a very robust dispersant to uniformly suspend these impurities throughout the oil so that they are removed from the engine when the old oil is drained.
Sometimes these suspended impurities cause the used oil to appear darker than other oils. This is a sign that Exxon Elite oil is doing its job to keep your engine clean.

This is usually a sign that Exxon Elite oil is suspending some sludge containing wear metals left by your previous oil. This usually returns to normal after the sludge has been solubilized by Exxon Elite oil and removed from the engine.

The process takes only 2-3 drain intervals, after which your wear metals will return to a more normal level or even a bit lower due to Exxon Elite oil's superior antiwear additive package.
ExxonMobil Technical Support can review each situation individually.

Let's look at lower oil consumption first. Exxon Elite oil is more viscous at ring zone temperatures than other oils, especially monograde oils (SAE 50 and lower). Because it is thicker, not as much of it slides by the rings during combustion. And this, of course, is often seen as a measureable decrease in oil consumption.

As for those fewer cases where oil consumption moves the other direction, impurities are created in your engine as a byproduct of combustion. These impurities can sometimes form sludge and deposits in the ring zone area of the pistons in your engine. Because Exxon Elite oil is formulated with a very robust dispersant, it may begin to suspend some of the sludge and deposits, resulting in a temporary increase in oil consumption as oil slides by the backside of the rings. In these cases, oil consumption usually returns to normal after 2-3 drain intervals.

Oil pressure is directly proportional to oil viscosity. Accordingly, your oil pressure using Exxon Elite oil will change to the extent that its viscosity is different from the viscosity of the oil you were previously using. For example, if you were previously using an SAE 50 weight monograde, your oil pressure on startup will decrease because Elite is a 20W-50 multigrade and is thinner at ambient temperature.

At operating temperature, your oil pressure with Exxon Elite oil may be slightly higher than your oil pressure was with an SAE 50 weight monograde because Exxon Elite is slightly thicker at operating temperature.

Oil temperatures are set by the manufacturer of your engine and can usually be found in the Pilot Operating Handbook. Typically, you should operate you oil at 180 degrees Fahrenheit-185 F (normally aspirated engines). Maximum Oil temperature is usually 245 F.

Please check with your engine manufacturer for the recommendations for your specific engine.

The shelf life of Exxon Aviation Oil Elite 20W-50 engine oil is 10 years in quarts and five years in drums. The date of manufacture can be determined using the batch and fill codes printed on each bottle.

ExxonMobil rationalized all of our automotive products around the world to a common bottle – and we picked as a standard the bottle opening used in Europe.

Because we are not able to make changes to the packaging line during packaging runs of aviation piston oil, we must use the same bottle as all other product lines. Although we are prohibited from offering our preferred smaller opening, we are committed to finding other ways to keep our customers happy.

Grease and gear oils

In the past, helicopter OEMs have relied upon MIL and DOD specification products in gearbox applications. Most common among these recommendations is the use of MIL-PRF-23699 turbine oil. Alternately, some OEMs recommend synthetic gear oil specifications such as DOD-PRF 85734 and MIL-PRF-6086. Each are 5 cSt specifications and have been around for many years.

The unique performance characteristics and viscosity (10.9 cSt) of Mobil AGL lubricant provide improved wear protection and extreme temperature performance. Mobil AGL gear lubricant is formulated to meet the demands of today’s helicopter transmissions designed for increased horsepower capacity.
Operators received instructions and guidance directly from the OEM in regards to this change. Operators should consult conversion guidance available from the OEM for specific considerations related to any lubricant conversions. Where Mobil AGL gear lubricant is recommended by the OEM, and when switching from Mobil SHC 626 oil, operators can begin using Mobil AGL for future service fill including top-off.

The newer formulation of Mobil SHC 626 oil and all other Mobil SHC™ 600 Series oils are clearly labeled “NOT FOR AVIATION USE.” Additionally, the latest formulation of Mobil SHC 600 Series oils has been updated with Mobil SHC™ brand logos on the labels, which differentiate them from the older formulation package labels. A supplemental letter was provided that includes examples of these labels.
Mobil SHC 600 series gear oils were formulated for compatibility with industrial systems. They are “NOT FOR AVIATION USE,” meaning that they were not designed, or recommended, for lubrication of aircraft components
No. Although Mobil AGL lubricant and Mobil SHC 626 oil are fully miscible with each other, Mobil SHC 626 was not designed, or recommended, for lubrication of aircraft components, and should not be used interchangeably.

Mobil AGL gear lubricant has been approved for use by helicopter manufacturers in specified gearbox applications. MD Helicopter, Erickson Air-Crane and Boeing have recommended Mobil AGL lubricant. Operators should consult their service manuals and OEM representatives for specific guidance.

What you are seeing is a phenomenon called oil separation, and it is normal for greases to exhibit some degree of oil separation.
In the most basic terms, grease is oil that has been mixed into a soap in order to hold the lubricating oil in place. However, some degree of oil separation from the soap is necessary for the oil to provide lubrication to the intended application. Oil separation varies with storage geometry, time and temperature. But separation is normal. As long as the oil is not leaking from any seals in the airplane, the oil will perform its intended task.
Oil does separate from grease – both in use and in storage. And the lower the viscosity of the base oil used in the grease, the more separation you are likely to see. For example, the base oil viscosity of Mobilgrease 33 grease is lower than the base oil viscosity of Mobilgrease 28 grease, and the rate of oil separation is correspondingly higher.
If oil is collecting around the dome or in the crevices at the top of a pail of grease, this is considered normal, and the oil can be remixed into the grease. If, however, the surface of the pail is completely covered with a layer of separated oil, then operators should contact ExxonMobil aviation.

If the separation appears normal, the oil can be mixed back into the grease. Refer to the aviation shelf life bulletin, which addresses the process for remixing the oil and soap in a container in which you see separation.

Basically, it says to remix the separated oil into the top 2.5 cm of grease.

You can help minimize oil separation by releasing pressure on the pumping devices used to apply the grease when not in use.

Please contact your ExxonMobil aviation representative.

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