Frequently asked questions
Find answers to the most commonly asked questions about ExxonMobil Aviation products and services.
Q. There are many acronyms used in the aviation industry. What do they mean?
A. 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
Q. What do the dates on the certificate of analysis refer to?
A. 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
Q. What date should I use to determine shelf life remaining?
A. 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
Q. What is a Jet oil?
A. 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 minus -40°C, 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.
Q. Why are the Mobil Jet™ oils sold in metal quart cans?
A. 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 (i.e. dust, dirt, etc.), therefore it is recommended for single use application only.
Q. What is the shelf life for Mobil Jet oil products?
A. The shelf life for all Mobil Jet oils in metal quarts is 10 years and 5 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.
Q. How should the Mobil Jet oils be handled?
A. 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 JetT™ Oil 254 have excellent additive compatibility and long-term storage stability characteristics.
Q. How do we obtain a certificate of compliance for Mobil Jet oils?
A. A certificate of compliance is a document similar to what's commonly referred to as a Certificate of Analysis (COA). COA's 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.
Q. Why is Mobil Jet Oil 254 darker in color?
A. 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.
Q. Are Mobil Jet oils compatible with competitive aviation gas turbine oils?
A. Yes, they are compatible. The oil approval process includes compatibility testing for all jet oils. Approval requirements mandate that jet oils must be 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.
Q. How do I change a system from an existing brand to a Mobil Jet oil?
A. 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 (i.e. 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% of the new oil in a few hundred hours of operation.
Q. What are the differences between a land based turbine installation and those that operate in the aviation environment?
A. 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 build up 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.
Q. Are Mobil Jet oils compatible with elastomers, plastics, metals and seals?
A. Mobil Jet oils are compatible with the materials provided under normal conditions of jet engine operation. For compounds and components (i.e. 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.
Q. Are jet oils hazardous or toxic?
A. 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.
Q. What is a hydraulic fluid and how is it used?
A. 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.
Q. How are Exxon HyJet™ IV-Aplus and Exxon HyJet™ V different from conventional hydraulic oils (MIL-PRF-5606)?
A. HyJet IV-Aplus and 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.
Q. Why are HyJet products purple?
A. Fire resistant hydraulic oils are dyed purple to differentiate them from 5606 fluids which are red in color.
Q. Are there any special handling requirements for HyJet products?
A. 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.
Q. What is the shelf life for Exxon HyJet IV-A plus and Exxon HyJet V?
A. The shelf life of Exxon HyJet IV-Aplus and Exxon HyJet V is 10 years for quarts and gallons, and 5 years in pails and drums. The date of manufacture can be determined using the batch and fill codes printed on each package.
Q. Are HyJet fluids compatible with other hydraulic fluids, elastomers, plastics, metals and seals?
A. 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.
Q. How do I convert an aircraft hydraulic system from a competitive product to a HyJet product?
A. 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.
Q. Do you have a hydraulic fluid analysis program?
A. Yes, ExxonMobil Aviation offers Exxcare as a routine in-service fluid analysis program for HyJet customers.
Q. What is the difference between Exxon HyJet IV-Aplus and Exxon HyJet V?
A. HyJet V offers extended fluid life over HyJet IV-Aplus without sacrificing fluid performance in preventing wear, rust and deposits or increasing weight. HyJet V is also certified for use in 5,000 psi hydraulic systems.
Q. What is semi-synthetic oil? Why use synthetics?
A. 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.
Q. What is a multigrade oil and why should I use one?
A. 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.
Q. Is Exxon Aviation Oil Elite™ 20W-50 any different than other oils?
A. Yes. Exxon Elite 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 also has a highly effective dispersant that will provide excellent deposit control.
Q. Why should I use Exxon Elite?
A. There are many compelling reasons for all aircraft owners to try it. Exxon Elite can provide advantages over virtually all other commercial aviation oils currently on the market. Some consumers may find that Exxon Elite gives them better wear and corrosion control versus their current lubricant. Others may find better rust protection. Still others may find that Exxon Elite is better in all of these categories.
Q. Is Exxon Elite OEM approved? Is it U.S. military approved?
A. Yes. Exxon Elite is an SAE J1899 certified oil. That means it meets the requirements of engine OEMs and the U.S. military for ashless dispersant-containing oils. It meets MIL-L-22851D (obsolete) and is U.S. military approved.
Exxon Elite also has FAA Supplemental Type Certificates for Lycoming and Continental engines. The FAA has further approved Exxon Elite as an Alternate Method of Compliance with Airworthiness Directive 80-04-03-R2, paragraph b.1, which requires the use of an anti-wear/anti-scuffing additive in some Lycoming engines. A Special Airworthiness Information Bulletin stating this fact has been issued by the FAA: SAIB No. NE-00-22.
Q. What is the anti-wear/anti-scuffing additive you're referring to, and why is it important?
A. The anti-wear/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 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.
Q. If I use Exxon Elite can I extend my drain intervals?
A. 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.
Q. Can I mix Exxon Elite with conventional mineral oils – either monogrades or multigrades?
A. 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.
Q. Can I use supplemental additives with Exxon Elite?
A. While supplemental additives will probably do no harm, their use is not recommended. With the exception of the anti-wear/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 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, and 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.
Q. Will Exxon Elite help my engine make it to TBO (time between overhaul)?
A. 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's formulation provides excellent protection against wear, corrosion and rust.
Q. Are there any restrictions as to type/age of airplane for using Exxon Elite?
A. Exxon Elite 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.
Q. Do I need a special oil filter with Exxon Elite?
A. No. Exxon Elite requires no special filtration.
Q. Will ExxonMobil ever produce an extended-TBO oil?
A. 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.
Q. Sometimes I see a white, milky substance (sometimes described as foam) in the area of the oil filler neck or dip stick. What is this substance?
A. 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 you 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. 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 will do its job in protecting against rust from this type of moisture.
Q. Why does Exxon Elite turn dark very early in the drain interval? (This may be especially pronounced right after converting to Exxon Aviation Oil Elite 20W-50)
A. 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 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 is doing its job to keep your engine clean.
Q. The wear metals in my used oil analysis increased immediately after converting to Exxon Elite. What caused this?
A. This is usually a sign that Exxon Elite 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 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's superior anti-wear additive package.
ExxonMobil Technical Support can review each situation individually.
Q. I saw a change in oil consumption after converting to Exxon Elite. What's going on with oil consumption?
A. Let's look at lower oil consumption first. Exxon Elite 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 by-product of combustion. These impurities can sometimes form sludge and deposits in the ring zone area of the pistons in your engine. Because Exxon Elite 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.
Q. Why does oil pressure sometimes change right after converting to Elite?
A. Oil pressure is directly proportional to oil viscosity. Accordingly, your oil pressure using Exxon Elite 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 may be slightly higher than your oil pressure was with an SAE 50 weight monograde because Exxon Elite is slightly thicker at operating temperature.
Q. What is the recommended oil temperature for Exxon Elite? What is the maximum oil temperature?
A. 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°-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.
Q. What is the shelf life for Exxon Aviation Oil Elite 20W-50?
A. The shelf life of Exxon Aviation Oil Elite 20W-50 is10 years in quarts and 5 years in drums. The date of manufacture can be determined using the batch and fill codes printed on each bottle.
Q. Why did ExxonMobil change the bottle opening of Exxon Aviation Oil Elite 20W-50?
A. 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.
Q. What is the major difference between Mobil AGL™ Synthetic Aviation Gear Lubricant and other products that are traditionally used in helicopter transmissions?
A. In the past, helicopter OEMs have relied upon MIL and DOD specification products in gear box 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.
Mobil AGL’s unique performance characteristics and viscosity (10.9 cSt) provide improved wear protection and extreme temperature performance. Mobil AGL is formulated to meet the demands of today’s helicopter transmissions designed for increased horsepower capacity.
Q. What instructions should helicopter operators follow when switching from the current Mobil SHC 626 to Mobil AGLTM Synthetic Aviation Gear Lubricant?
A. 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 is recommended by the OEM, and when switching from the current formulation of Mobil SHC 626, operators can begin using Mobil AGL for future service fill including top-off.
Q. How can operators tell the difference between current Mobil SHC 626 product and the newer formulation of Mobil SHC 626?
A. The newer formulation of Mobil SHC 626 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.
Q. Why does the latest formulation Mobil SHC 600 Series labels and PDS contain the statement "NOT FOR AVIATION USE"?
A. 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
Q. Was a statement provided to customers regarding compatibility of Mobil AGL and the latest formulation of Mobil SHC 626 labeled “NOT FOR AVIATION USE”?
A. No. Although Mobil AGL and Mobil SHC 626 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.
Q. What actions should be taken in the event that helicopter operators mistakenly fill or top-off their helicopter gear-box with the latest formulation Mobil SHC 626 labeled “NOT FOR AVIATION USE”?
A. They should inform their helicopter OEM they used unapproved oil and seek their advice.
Q. What approvals does Mobil AGL Synthetic Aviation Gear Lubricant have?
A. Mobil AGL Synthetic Aviation Gear Lubricant has been approved for use by helicopter manufacturers in specified gear box applications. MD Helicopter, Erickson Air-Crane, and Boeing, have recommended Mobil AGL Synthetic Aviation Gear Lubricant. Operators should consult their service manuals and OEM representatives for specific guidance.
Q. When we open pails of grease we sometimes see oil floating on top. What is this?
A. What you are seeing is a phenomenon called oil separation, and it is normal for greases to exhibit some degree of oil separation.
Q. Why does oil separate?
A. 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.
Q. Why do we see more oil separation with Mobilgrease™ 33 than with Mobilgrease™ 28?
A. 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 is lower than the base oil viscosity of Mobilgrease 28 and the rate of oil separation is correspondingly higher.
Q. What is normal?
A. 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.
Q. What do we do when we see normal oil separation?
A. 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.
Q. Is there anything we can do to minimize oil separation?
A. You can help minimize oil separation by releasing pressure on the pumping devices used to apply the grease when not in use.
Q. What do we do when we think oil separation is abnormal?
A. Please contact your ExxonMobil Aviation representative.