AeroShell Fluid 31 Aircraft Hydraulic Fluid

AeroShell Fluid 31 is a synthetic, low-viscosity aircraft hydraulic fluid designed for high-performance hydraulic systems that demand excellent stability and reliability. It is formulated with synthetic hydrocarbon base oils and a proprietary additive package to provide superior low-temperature performance, oxidation stability, and wear protection. Because it resists breaking down under extreme pressure and thermal stress, AeroShell Fluid 31 is widely used in modern commercial, military, and high-performance aircraft. Its exceptional cleanliness also supports the precise operation of advanced hydraulic components.

AeroShell Fluid 31 is commonly used in hydraulic systems powering landing gear, flight controls, thrust reversers, and brake systems. Its strong anti-wear properties help protect pumps, actuators, and valves from premature wear, even in high-pressure environments. With its excellent thermal and oxidative stability, the fluid ensures consistent responsiveness and reliable power transmission across a wide range of temperatures. This makes it a preferred choice for operators who fly in diverse climates and require dependable hydraulic performance.

AeroShell Fluid 31 is formulated with synthetic hydrocarbon base oils, also known as polyalphaolefins (PAOs). These synthetic oils offer superior low-temperature behavior and enhanced thermal stability when compared to mineral-based hydraulic fluids. The result is a fluid that maintains optimal viscosity, resists evaporation, and prevents deposit formation in high-stress environments. Its synthetic composition contributes significantly to its extended service life and overall system cleanliness.

AeroShell Fluid 31 is engineered to operate effectively across a temperature range of approximately -40°F to  401°F (-40°C to 205°C). This wide operating window ensures reliable performance during cold starts, high-altitude flights, and hot-weather operations. Even at extremely low temperatures, the fluid maintains sufficient flow and responsiveness, which is essential for aircraft that operate in arctic or winter environments. At high temperatures, its synthetic formulation protects against viscosity loss and thermal breakdown.

Unlike MIL-PRF-5606, which is a mineral-based hydraulic fluid, AeroShell Fluid 31 is a synthetic PAO-based formulation designed for superior thermal stability and broader temperature performance. AeroShell Fluid 31 also offers significantly greater fire resistance, making it a safer choice for aircraft operating in high-heat environments. Additionally, it resists oxidation better than 5606, which helps reduce varnish, sludge, and other deposits that can impair hydraulic components. Many operators upgrade to AeroShell Fluid 31 for improved safety, longer service life, and enhanced cold-weather functionality.

Yes, AeroShell Fluid 31 offers improved fire resistance compared to older mineral-based hydraulic fluids such as MIL-PRF-5606. Its synthetic formulation raises the flash point and reduces the risk of fluid ignition during leaks or high-temperature events. While not entirely fireproof like phosphate-ester fluids, AeroShell Fluid 31 offers a meaningful safety advantage in high-temperature applications. This increased fire resistance contributes to its widespread use in modern aircraft hydraulic systems.

AeroShell Fluid 31 is designed to be compatible with most common materials used in aircraft hydraulic system seals, including nitrile rubber and fluorocarbon elastomers. Its synthetic formulation reduces the risk of swelling, shrinkage, or hardening of seals when used within manufacturer-approved systems. However, operators should always review OEM guidelines to ensure full compatibility. Proper material compatibility helps extend seal life and minimize hydraulic leaks.

Mixing AeroShell Fluid 31 with other hydraulic fluids is not recommended unless specifically approved by the aircraft or component manufacturer. Different fluid chemistries – especially between mineral and synthetic formulations – can lead to additive clashes, viscosity changes, or reduced fire resistance. Before switching to AeroShell Fluid 31, it is best practice to flush the system and remove residues of the previous fluid. This ensures optimal performance and avoids unpredictable behavior within the hydraulic system.

AeroShell Fluid 31 provides exceptional low-temperature fluidity, making it ideal for cold-weather operations and high-altitude flight. It offers strong anti-wear and corrosion protection, helping extend the life of pumps, actuators, and valves. Its synthetic formulation resists oxidation and thermal breakdown, reducing the formation of varnish and deposits that can compromise hydraulic performance. Operators also benefit from improved system cleanliness, extended fluid life, and enhanced reliability across a wide range of operating conditions.

AeroShell Fluid 31 is widely used in modern jets, turboprops, and military aircraft requiring a low-viscosity, synthetic hydraulic fluid with excellent thermal stability. It is especially popular in aircraft designed for extreme environments or that rely on high-pressure, high-performance hydraulic systems. Many commercial airlines and defense operators specify AeroShell Fluid 31 for its strong safety, reliability, and long-term maintenance benefits. Its broad approval list makes it suitable for a wide range of airframes and components.

AeroShell Fluid 31 remains extremely fluid and responsive at very low temperatures, allowing hydraulic systems to function reliably during cold starts and high-altitude operations. Unlike some mineral-based fluids that thicken in cold conditions, Fluid 31 maintains stable viscosity and flow characteristics. This ensures quick system response and reduces the risk of sluggish actuators or pump cavitation. Its cold-weather performance is one of the reasons it is preferred for aircraft operating in northern or arctic regions.

Yes, AeroShell Fluid 31 is engineered for outstanding oxidation stability, helping prevent the formation of varnish, sludge, and deposits. Its synthetic base oil and additive package resist chemical breakdown at high temperatures and under prolonged system stress. This stability helps maintain hydraulic cleanliness, extend fluid service intervals, and improve overall component life. It is one of the defining advantages of using synthetic PAO-based fluids in modern aircraft.

Service life depends on the aircraft, operating conditions, and maintenance practices, but AeroShell Fluid 31 generally offers longer service intervals than mineral-based fluids. Its high oxidative stability slows degradation, allowing the fluid to remain effective for extended periods. Regular fluid analysis is still recommended to monitor contamination levels and overall condition. Many operators find that AeroShell Fluid 31 reduces maintenance frequency and supports more predictable hydraulic system performance.

Like all aviation hydraulic fluids, AeroShell Fluid 31 should be handled with care. Prolonged skin or eye contact should be avoided, and appropriate PPE – such as gloves and eye protection – should be worn during maintenance. The fluid should be used only in well-ventilated areas to avoid inhalation of mist or vapors. Always refer to the product’s Safety Data Sheet (SDS) for specific handling guidelines and safety recommendations.

AeroShell Fluid 31 should be stored in sealed containers in a clean, dry, temperature-controlled environment away from direct sunlight. Keeping containers tightly closed prevents moisture ingress and contamination, which can degrade the quality of the fluid. Proper storage helps preserve oxidation stability and ensures the fluid maintains its certified performance when put into service. Always follow manufacturer guidelines for long-term storage conditions and shelf-life expectations.