Aerospace Greases, Turbine Oils and Hydraulic Fluids

Updated October 12, 2026

Lubricant types and where they are used

Start from the equipment manual or drawing, which names the spec. The spec then fixes the temperature range, the base stock and the seals the fluid was tested against.

The specifications that govern aerospace lubricants

Every row below comes from the specification or its notice on EverySpec. Status is as shown there when we checked; later revisions may exist, so confirm on ASSIST before ordering.

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How the designation is built: class, grade and NATO code

Lubricant specs do not use part numbers in the hardware sense. The designation is the spec, the revision, and a class, grade or type, and each has a NATO code that identifies the same product across allied supply systems.

• MIL-PRF-23699G, Class HTS reads as a 5 centistoke synthetic ester turbine oil in the high thermal stability class, NATO O-154. The four classes are C/I corrosion inhibiting (O-152), HTS high thermal stability (O-154), STD standard non-corrosion inhibiting (O-156) and EE enhanced ester (O-167). The spec's acquisition paragraph tells buyers to state the class.
• MIL-PRF-7808L, Grade 3 reads as the normal grade (NATO O-148), which is supplied when no grade is specified. Grade 4 (NATO O-163) is specified when higher viscosity or greater thermal stability is needed.
• MIL-PRF-27617G, Type II reads as fuel and oxidizer resistant grease for -40 to 204 °C, NATO G-398.

The class matters in service. MIL-PRF-23699G intends STD oil for normal turbo equipment where corrosion during long downtime in moist conditions is not a concern, C/I where corrosion inhibition is wanted, HTS for hot running engines showing coking or oil degradation, and EE for improved fluorocarbon seal compatibility and load carrying.

Compatibility and mixing rules

Mixing is governed by the specs themselves, and the rules are narrower than many people assume.

• Turbine oils. MIL-PRF-23699G says all of its classes are interchangeable and fully compatible with each other, but mixing across classes diminishes the added benefit of C/I, HTS or EE oil and the mixture reverts to STD performance. It also states that its oils are not intended for gas turbine systems with silicone or fluorosilicone seals operating at elevated temperature.
• Hydraulic fluids. MIL-PRF-87257C calls its fluid completely compatible with MIL-PRF-5606, MIL-PRF-6083, MIL-PRF-46170 and MIL-PRF-83282 fluids, and says it may be interchangeable with them for some applications, with the choice depending on the system. MIL-PRF-83282D requires compatibility testing of candidate fluid mixed with MIL-H-5606 and MIL-H-87257 fluids.
• Greases. MIL-PRF-81322G and MIL-PRF-32014A each require a new product to be compatible with greases already qualified to that same specification, tested by mixing and seven days of storage. That test says nothing about mixing a grease from one spec with a grease from another. Treat cross-spec mixing as a change that needs engineering approval, and clean out the old grease when changing specs.

Seal compatibility is part of every fluid spec. MIL-PRF-23699G tests swell against standard elastomer stocks including SAE AMS3217/1, AMS3217/4, AMS7276 and AMS-R-83485. When a fluid change is proposed, check the O-ring compound against the new fluid before approving it.

Space, vacuum and oxygen service lubricants

Liquid oxygen and vacuum service narrow the choice sharply. MIL-PRF-27617 grease is intended for fuel systems and is also suitable as a lubricant for valves, threads and bearings in liquid oxygen service in aerospace vehicles and support equipment. The same spec warns that it may not be suitable for dynamic aluminum or magnesium bearings because of possible ignition hazards, which is the kind of limit that has to be carried onto the drawing. Oxygen service hardware also needs precision cleaning; see precision and oxygen cleaning.

In vacuum, the question is outgassing. NASA Goddard's outgassing database reports total mass loss and collected volatile condensable materials measured by ASTM E595, and it includes greases and lubricants as a category. Ask for the product's E595 data or its database entry when a lubricant is going near optics, sensors or other contamination sensitive surfaces, and apply your program's acceptance limits.

Where liquid lubricants are not acceptable, solid film lubricants take over. MIL-PRF-46010 covers a heat cured, corrosion inhibiting solid film lubricant, and MIL-PRF-46147 covers two types of air cured, corrosion inhibiting solid film lubricant. The selection and application detail is on dry film lubricants.

Storage, lots and shelf life

Fluids and greases are lot controlled products. MIL-PRF-83282D defines a bulk lot as a homogeneous quantity in a single container or made in a single plant run not exceeding 24 hours with no change in ingredients, and MIL-PRF-32014A uses a 48 hour limit. The lot number is what ties your container to the conformance tests.

Storage limits come from the spec and the manufacturer. MIL-PRF-83282D notes its fluid may be stored in areas ranging from -40 to +50 °C. Many lubricants carry a shelf life assigned by the manufacturer or by the DoD shelf life program, and the container date is what receiving checks. How dating and extensions work is on shelf life control.

Ordering checklist for lubricants

• Specification and revision, with class, grade or type, for example MIL-PRF-23699G, Class STD.
• Qualified product name and manufacturer. MIL-PRF-23699G points to the Qualified Products Database on ASSIST for current qualified oils; check the equivalent list for the spec you are buying.
• Container size and packaging. Several specs list packaging as an acquisition requirement.
• Manufacturer lot number, date of manufacture and shelf life or expiration on every container.
• Conformance test results for the lot where your program requires them; MIL-PRF-23699G lists submittal of conformance test results as an acquisition option, and certification of conformance to material prohibitions.
• Factory sealed containers only, no decanting or repacking.
• Certificate of conformance tracing to the manufacturer and lot. See certificates of conformance.

Counterfeit and quality risks, and how to receive lubricants

The common failures are commercial product relabeled as a mil spec product, decanted or repackaged containers with no lot traceability, expired stock, and the wrong class or grade. Fluid contamination is a quieter risk: a hydraulic fluid that meets the spec in the drum can fail a cleanliness requirement after being transferred through dirty equipment.

• Check that the product name on the container is on the qualified list for that spec and class.
• Match the lot number on the container to the certificate.
• Reject broken seals, hand labels and containers that are not the manufacturer's.
• Check dates against the minimum remaining life on the PO.
• For hydraulic fluid going into a system with a cleanliness class, ask how it will be tested before use.

See receiving inspection and counterfeit parts avoidance.

How we source greases, oils and fluids

We do not stock lubricants or publish prices. We source the qualified product through authorized distributors or the manufacturer, flow the spec, revision, class and shelf life requirement down on the order, and check lots, dates and certificates before shipping. We can put lubricants on the same PO as the bearings, seals and machined parts they serve, or pack them into a kit for a build or a launch campaign. When a spec has gone inactive, as MIL-PRF-5606 has for new design, we will source to the callout you have and flag the replacement specs so your engineering can decide. Hard to find legacy products go through our obsolete parts process.

Related pages: aerospace sealants, structural adhesives, and the chemicals category.

Get lubricants sourced with the hardware they serve

Send the spec, class or grade, container size, quantity and the remaining shelf life you need at receipt. A person replies within one business day with a source and the paperwork you will receive. Request a quote for lubricants and hardware. Back to all parts.

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Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.

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Related

• Aerospace Sealants: Specs, Dash Numbers and Buying
• Aerospace Structural Adhesives: Film, Paste and Specs
• Shelf Life Control: Buying and Receiving Age Sensitive Items

Sources

• MIL-PRF-23827C, Grease, Aircraft and Instrument, Gear and Actuator Screw (EverySpec)
• MIL-PRF-23827C Notice 2, 2016 (EverySpec)
• MIL-PRF-81322G, Grease, Aircraft, General Purpose, Wide Temperature Range (EverySpec)
• MIL-PRF-32014A, Grease, Aircraft and Instrument (EverySpec)
• MIL-PRF-27617G, Grease, Fuel and Oxidizer Resistant (EverySpec)
• MIL-PRF-7808L, Lubricating Oil, Aircraft Turbine Engine, Synthetic Base (EverySpec)
• MIL-PRF-23699G, Lubricating Oil, Aircraft Turbine Engine, Synthetic Base (EverySpec)
• MIL-PRF-83282D, Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base (EverySpec)
• MIL-PRF-87257C, Hydraulic Fluid, Synthetic Hydrocarbon Base (EverySpec)
• MIL-PRF-5606J, Hydraulic Fluid, Petroleum Base (EverySpec)
• MIL-PRF-46147D, Lubricant, Solid Film, Air Cured (EverySpec)
• NASA Goddard outgassing database (ASTM E595 data)