Blue sky view from the side of a plane

FAQs  

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.


  • airplane landing

    General questions

    Get background on common issues that aviation professionals face in their everyday operations.

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  • Aircraft engine viewed at night

    Jet turbine oils

    Explore details on Mobil Jet™ oils — designed to meet today and tomorrow’s aviation challenges.

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  • Exxonmobil Aviation hydraulic fluid protecting a valve.

    Hydraulic fluids

    Discover best practices and recommendations for our series of Mobil™ HyJet™ hydraulic fluids.

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  • propeller plane motor

    Piston engine oils

    What you need to know about using Exxon Aviation Oil Elite™ 20W-50 engine oil.

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  • Close up of bearings protected by ExxonMobil Aviation grease.

    Greases and gear oils

    Find insights on using our multipurpose airframe and wheel bearing greases and gear oils.

    Learn More

General questions

Here is a brief list of common industry terminology:

APU

Auxiliary Power Unit

CSD

Constant Speed Drive

IDG

Integrated Drive Generator

BPR

Bypass Ratio

TBO

Time Between Overhaul

MTBF

Mean Time Between Failures

MTBR

Mean Time Between Removals

SFC

Specific Fuel Consumption

EGT

Exhaust Gas Temperature

ETOPS

Extended Twin-engine Operations

IFSD

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.

Mobil HyJet IV-Aplus and Mobil 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. Mobil 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 Mobil 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 Mobil HyJet products is well documented in the MSDS.

The shelf life of Mobil HyJet IV-Aplus and Mobil 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.


Mobil 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 Mobil 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 Mobil HyJet customers.

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

The Mobil™ brand carries significant brand equity and is widely acknowledged as a premiere brand and leading supplier of high-performance lubricants. With the rebrand, our former Exxon products now align with and leverage the strength of the Mobil brand.

There will be no change in product formulation. The changes taking place are related to brand elements and GHS labeling requirements. Changes include:

  • The product brand will be changed from Exxon to Mobil. Exxon HyJet™ V will be rebranded to Mobil HyJet V. Exxon HyJet™ IV-Aplus will be rebranded to Mobil HyJet IV-Aplus.
  • The Running Tiger icon will be replaced with the Mobil Pegasus.
  • Quart and gallon size cartons will be harmonized to use a white Mobil branded carton. We are discontinuing the use of craft/brown cartons, which some countries and customers may have seen previously.
  • Warning labels are being added to the face of the packaging where applicable (Global Harmonized System (GHS) and the U.S. Occupational Safety and Health Administration (OSHA)).

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.

Greases and gear oils

Although aviation and other forms of lubrication greases have very similar formulations, aviation greases differ in the degree of quality assurance and product integrity demanded by the aviation industry.

Aviation greases also undergo a much higher level of scrutiny for quality assurance and quality control than similar industrial greases. They also undergo more extensive testing than other types of lubrication greases to assure compliance with OEM, military and civil specifications and requirements. In addition, aviation grease formulations cannot substitute new additives, base oils or thickeners without OEM, military and civil authority endorsement. In many cases, full requalification of the grease may also be required.

While many base oils and additives used in greases have a defined odor when fresh, odors can also be the result of in-service degraded grease. However, ExxonMobil aviation greases formulated from 100 percent polyalphaolefin (PAO) base oil, such as Mobilgrease™ 33, will minimize these objectionable odors. Greases containing an ester base stock may be susceptible to hydrolysis and could generate an odor.

Grease odor does not impact grease performance.

Depending on the storage conditions, duration and temperature, greases can exhibit some degree of oil separation. For example, higher oil separation in a grease can merely be a direct effect of formulating it with a lower-viscosity base oil.

If oil is collecting around the dome or crevices at the top of a grease pail, the oil can be remixed into the grease. If, however, the pail’s surface is completely covered with a layer of separated oil, then operators should contact their supplier before applying the grease.

Again, operators should be wary of instances where more than one type of grease is used to ensure that grease transfer does not cause incompatible greases to come in contact with each other. Incompatible greases may result in an increase in oil bleed.

For more information on oil bleed and grease separation, review the technical topic here.

You can help minimize oil separation by storing oils in a climate-controlled environment and releasing pressure on the pumping devices used to apply the grease when not in use.

Oil bleed is a term used to explain the separation of oil or seepage of oil from the grease during normal operating or storage conditions. Oil bleed is easily identified by the presence of oily sections of greased components and/or the formation of small pools of oil around componentry.

Excessive oil bleed can impact a grease by causing it to harden, rendering it unsuitable for use.

ExxonMobil aviation greases are all expertly formulated to deliver exceptional performance and component protection even under extreme operating conditions. Each of our aviation greases delivers exceptional performance over wide temperature ranges:

  • Mobilgrease™ 28 – A multipurpose airframe and wheel bearing grease for plain and rolling bearings with an operating temperature range of -54ºC to 177ºC (-65ºF to 350ºF)

  • Mobilgrease™ 33 – A high-performance, BMS3-33-approved multipurpose airframe grease with an operating temperature range of -73 ºC to 121ºC (–100ºF to 250ºF)

  • Mobil™ Aviation Grease SHC 100 – An advanced wheel bearing grease with an operating temperature range of -54ºC to 177ºC (-65ºF to 350ºF)

Flash point is the lowest temperature at which a grease gives off sufficient vapors that will ignite in air when exposed to an ignition source. The flash point of a grease is often governed by the flash point of the oil used in the grease.

Over-greasing of a bearing or component can lead to a number of issues, including high operating temperatures, seal failures and bearing failures.

The most common visual indicators to help you determine if a grease needs to be replaced are to look for any hardening, softening or significant color changes. More advanced techniques involve vibration analysis, used grease analysis or thermal imaging. A detailed lubes program analysis by your supplier will help you identify the key features you need to assess grease life in service.

A number of options exist for removing grease from your application or bearing. These can range from purging and wiping down the part to solvent washing of the part. It is generally recommended that you contact your OEM supplier to determine what is an acceptable method to clean the application or bearing.

Base oils can consist of a wide range of fluids from low-viscosity mineral oils to heavy cylinder stocks to specialized synthetic lubricants. The inherent features seen in a base oil may also be seen in the grease, such as good high-temperature performance, oxidation resistance or low-temperature performance. Base oil selection is generally determined on the desired performance features of the grease.

No, not all greases are compatible, and the mixing of grease brands should not be taken lightly. If commingled greases are incompatible, the grease intermixing can result in reduced performance. All greases contain base oils, thickening agents and chemical additives that can interact adversely if incompatible greases are mixed.

To confirm if grease formulations are compatible, operators can consult the Standard ASTM D6185– Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases, which is based on performance data from testing mixtures of both greases. 

Most OEM, industry and supplier recommendations suggest performing a compatibility test to assess the risk of mixing two greases. Standard compatibility tests may consider the stability of the oil/thickener matrix by evaluating a grease’s shear stability, dropping point, storage stability and high-temperature performance.

ExxonMobil aviation has tested many combinations of greases to find that compatibility is generally “borderline.” The normal aviation industry practice is to fully purge all old greases from any application, regardless of compatibility. This is a standard operating practice and should be followed without exception.

For more information on grease compatibility and for conversion guidance, please review the technical topic here.

When incompatible greases are mixed together, the consistency typically becomes harder or softer than the individual greases. These consistency changes generally become more pronounced as operating temperatures and/or the rate of shearing increases.

While in operation, incompatible greases may also exhibit excessive oil separation or bleeding tendencies.

Grease oxidation is not a well-defined occurrence and can take many forms, including consistency change (harder or softer), color change, odor generation, increase in noise from the component or a temperature increase of the component.

The most common methods to screen for grease oxidation are vibration testing or thermal imaging of the component. An increase in either could be a sign of the grease oxidizing.

Shelf life specifications can differ between aviation greases. While the average industry shelf life of aviation greases is about three years, ExxonMobil aviation greases offer extended shelf life beyond the industry average, ranging from six to 10 years – more than double the industry standard.

ExxonMobil aviation grease shelf life is listed as the “use by” date on the container. To maximize shelf life, normal storage temperatures should range from 0°C to 40°C (32°F to 104°F), and containers should be kept indoors in a clean and dry environment to avoid hydrolysis and other environmental factors.

Mobilgrease™ 33 and Mobilgrease™ 28 aviation airframe greases have a shelf life of 10 years, more than three times the industry standard.

Mobil™ Aviation Grease SHC 100 has a shelf life of six years – double the industry standard.

Grease containers should be stored indoors in dry, cool and clean environments. Normal storage temperatures should range from 0°C to 40°C (32°F to 104°F). In the event that a stored grease is briefly exposed to severe temperatures or environmental conditions, technicians should consult their suppliers with concerns.

Once a container is opened, the grease should be used as soon as possible to avoid potential contamination. Since the rate of grease degradation can be impacted by exposure to contamination and storage and handling conditions, the listed shelf life recommendation for a grease is no longer applicable once a container is opened.

For more information on storage and handling best practices, review our technical topic here.

As the application temperature increases, the viscosity of a grease’s base oil will decrease.

When selecting greases, operators should also consider the base oil’s viscosity index, which measures an oil’s change in viscosity at different temperatures. Typically, greases formulated with synthetic base oils have a higher viscosity index compared to mineral base oils and will experience less base oil viscosity loss at higher temperatures.

As a result of the 10-year shelf life associated with Mobilgrease™ 33 and Mobilgrease™ 28, operators can reduce waste disposal, carrying costs and inventory turnover.

Extensive testing and research conclude that ExxonMobil aviation greases are capable of delivering the same quality of benefits throughout their full lifespan. According to this quality assessment, operators can safely rely on these greases to potentially reduce costs and continue to support their sustainability efforts for extended periods of time.

Mobil™ Aviation Grease SHC 100 carries a six-year shelf life, which is more than double the shelf life of similar greases. In addition, Mobilgrease 28 is approved for use as both a multipurpose airframe and wheel bearing grease, making it useful for operators looking to consolidate grease inventories, reduce waste and lower operating costs.

We recommend that exposure to high water concentrations, including precipitation and de-icing fluids on the tarmac, be avoided. Potential issues could involve hardening or softening of the greases, increased corrosion or decreased effectiveness of the performance additives. For greases formulated with ester base stocks, you may see increased hydrolysis or breakdown of the grease. To be safe, we recommend that technicians should evaluate their grease every 10,000 hours for irregularities and consult their supplier with any questions. Hydrolysis is preventable.

The use of contaminated greases can cause a wide range of issues, including deposit formation, reduced wear protection, increased wear, increased corrosion and reduced bearing life. We recommend that if a contaminated grease is used, the grease must be replaced immediately and the part should be examined for potential damage.

Grease color changes in-service can be a result of operating temperatures well above a grease’s temperature rating, or a result of contamination (e.g., dust from carbon brake that causes wheel bearing grease to appear dark).

In some airframe applications, a black grease may signify hydrolysis of the ester base oil or grease, identified with some BMS3-33 and MIL-PRF-23827 approved greases.

Changes in grease color can be the result of a number of factors, some of them more negative than others. For instance, the change can merely be caused by a change in the chemical dye used in the grease.

However, if the color change is caused by high temperatures, contamination or reactions with other substances, the color change may indicate a change in grease performance. Some of these effects include:

  • Chemical changes in a grease’s base oils or additives, such as hydrolysis, which may reduce the load-carrying or structural stability of the grease

  • Presence of particle contamination that can cause premature wear of bearings or affect grease quality

  • Reaction with unknown material may cause a change in color

The color of fresh grease is simply a function of dyes added to the formulation, which is often required by aviation industry organizations such as SAE International Aerospace or by an OEM QPL-specific directive. Other greases are required by specifications to be free of dyes.

Different grease colors sometimes help to avoid accidentally mixing greases; however, greases with the same color are not always compatible. For more information on aviation grease color, please review the technical topic in full here.

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