Fluorosilicone oil significantly outperforms methyl silicone oil in terms of fuel resistance, primarily due to the special chemical stability and solvent resistance conferred by the fluorine elements introduced into its molecular structure.
I. Core Performance Differences
1. Chemical Structure and Stability
Fluorosilicone oil: The main molecular chain is a siloxane structure, and the side chain contains trifluoropropyl groups (-CF₃), forming an "electron shielding effect," giving the molecule extremely strong chemical inertness. This structure provides it with natural resistance to polar substances such as fuels and solvents.
Methyl silicone oil: Contains only methyl (-CH₃) side chains, lacking the protection of fluorine elements, resulting in higher molecular polarity and a greater tendency to interact with fuel components.
2. Specific Performance in Fuel Resistance
Fluorosilicone oil:
After long-term immersion in aviation fuel, gasoline, diesel, etc., the volume change rate is ≤25% (23℃ × 24 hours).
It can resist fluorinated coolant (HEXAFLUO BoreafTM) media, showing zero corrosion.
Maintains stable physical properties in a 500-hour methanol gasoline immersion test.
Suitable for lubrication of compressors and valves in contact with liquid oxygen, oxygen, corrosive and oxidizing gases.
Methyl silicone oil:
Limited fuel resistance; long-term contact with fuel leads to volume expansion and performance degradation.
Only suitable for non-polar or weakly polar environments; easily swells and fails in polar solvents (such as alcohol, acetone) or mineral oil.
When used in fuel systems, special modifiers need to be added to improve its resistance.
3. Temperature Range and Adaptability to Fuel Environments
Fluorosilicone oil: Operating temperature range -60℃ to 250℃, remains soft and does not harden at low temperatures, and does not easily volatilize or coke at high temperatures. Particularly suitable for extreme temperature environments such as aviation and automotive fuel systems.
Methyl silicone oil: Operating temperature range -50℃ to 180℃, prone to waxing or significant viscosity reduction in high-temperature fuel environments, leading to decreased lubrication function. 4. Surface Characteristics and Material Compatibility
Fluorosilicone oil: Extremely low surface tension (20-25 mN/m), forming a low-surface-energy protective layer that is not easily contaminated by oil. It has good compatibility with oil-resistant rubbers such as EPDM and NBR, and does not cause material swelling or embrittlement.
Methyl silicone oil: Higher surface tension, may cause swelling in natural rubber, and its performance deteriorates after prolonged contact with mineral oil.

II. Comparison of Application Fields
Typical Applications of Fluorosilicone Oil
Aerospace: Aircraft fuel tank sealing rings, base components for hydraulic system lubricants.
Automotive industry: Automotive oil seals, fuel hoses, oil pressure system sealing rings.
Military industry: Hydraulic system bellows for military aircraft, sealing strips for special vehicle doors and windows.
Chemical industry: Corrosion-resistant and solvent-resistant defoamers, lubricants, and greases.
Typical Applications of Methyl Silicone Oil
Electrical insulation: Impregnation of transformers and capacitors, and insulation treatment of electronic instruments.
Mechanical protection: Buffering agents for automotive internal combustion engines, shock-absorbing materials for precision instruments.
Surface treatment: Waterproof, mildew-proof, and insulating films for glass and ceramic surfaces.
Medical field: Surface lubrication treatment of medical devices, excipients for anti-bloating tablets and burn ointments.

III. Selection Recommendations
Prioritize fluorosilicone oil: When the application involves fuel systems, polar solvent environments, and wide temperature range requirements (especially low-temperature environments), fluorosilicone oil is a more reliable choice, although its cost is 3-5 times that of ordinary silicone oil.
Prioritize methyl silicone oil: In conventional lubrication, electrical insulation, moisture-proof and dust-proof applications, and other non-fuel contact environments, methyl silicone oil remains an ideal choice due to its cost advantage and good overall performance.
By introducing fluorine elements into the siloxane main chain, fluorosilicone oil achieves a qualitative leap in fuel resistance, making it the preferred material in demanding environments such as aerospace and automotive fuel systems, while methyl silicone oil maintains its economical and practical advantages in conventional application fields.