The material compatibility of fluorosilicone oil in automotive rubber seals is highly dependent on the chemical structure of the seal's base material.  Its compatibility can be clearly categorized into three types: excellent match, partial compatibility, and incompatibility.

Excellent Match: Fluorosilicone Rubber (FVMQ)
Fluorosilicone oil and fluorosilicone rubber (FVMQ) have high chemical compatibility. Both belong to the fluorinated siloxane system, have similar molecular structures, and exhibit excellent interfacial compatibility. Under long-term contact, FVMQ seals show almost no swelling, softening, or mass loss in fluorosilicone oil environments, with a volume change rate of less than 1%.
Its resistance is particularly outstanding under extreme conditions:
After immersion in ethanol gasoline (E85) for 500 hours, the tensile strength retention rate is >95%, and the hardness change is <5 Shore A;
It maintains stable elasticity over a wide temperature range of -89℃ to 232℃, and its resistance to compression set is superior to traditional fluororubber;
It is inert to fuel, brake fluid, and antifreeze, making it the preferred sealing combination in high-temperature, highly corrosive environments.

Partial Compatibility: Hydrogenated Nitrile Butadiene Rubber (HNBR)
The compatibility of fluorosilicone oil with HNBR is better than with ordinary NBR, but there is still a moderate risk of swelling. Experimental data shows:
After immersion in fluorosilicone oil at 125℃ for 168 hours, the volume expansion rate of HNBR is approximately 3%~5%;
Tensile strength retention rate is >85%, hardness change is <10%, and no cracking or embrittlement occurred;
Suitable for low dynamic stress and medium temperature environments (such as static seals in gearbox housings and oil pan gaskets), but not recommended for high-pressure oil lines or high-frequency vibration areas.

Incompatible: Nitrile Butadiene Rubber (NBR) and Silicone Rubber (VMQ)
NBR: Due to the presence of polar acrylonitrile groups, there is a "polarity mismatch" with the non-polar fluorocarbon chains in fluorosilicone oil, leading to significant swelling. In a gasoline environment, NBR can experience a volume expansion rate of 15% to 25%, leading to decreased hardness, loss of elasticity, and a high risk of fuel leakage.
VMQ (ordinary silicone rubber): Although it shares the same siloxane main chain, it lacks fluorinated side groups. The fluorocarbon components in fluorosilicone oil can easily migrate and permeate, causing VMQ to soften, become sticky on the surface, and experience increased compression set, resulting in a high risk of seal failure after prolonged use.

Material Selection Recommendation Comparison Table
Seal Material | Compatibility with Fluorosilicone Oil | Recommended Application Scenarios | Risk Warning
FVMQ (Fluorosilicone Rubber) | Excellent | High-temperature oil seals, fuel systems, EV battery cooling lines | Higher cost, requires custom processing
HNBR | Moderate | Static seals, medium-temperature oil line gaskets | Avoid prolonged contact with high-concentration fluorosilicone oil
FKM (Fluorocarbon Rubber) | Incompatible | Prohibited from contact | May experience phase separation and interfacial debonding
NBR | Severely Incompatible | Prohibited from use | Rapid swelling, seal failure
VMQ (Silicone Rubber) | Incompatible | Prohibited from use | Fluorine migration leads to softening and adhesion