Abstract: The invention provides a fluid composition for a fluid coupling, which is excellent in viscosity stability and torque stability, and comprises a polyorganosiloxane base oil having a viscosity of 3,000-500,000 mm.sup.2 /sec at 25.degree. C. and at least one 5-membered heterocyclic compound incorporated in a proportion of 0.01-3.0 wt. % based on the total weight of the composition, said 5-membered heterocyclic compound being selected from the group consisting of thiadiazole derivatives and thiazole derivatives, both, having at least one monovalent group represented by the formula --S.sub.x --R.sup.6 in which R.sup.6 is a saturated or unsaturated monovalent group or atom composed of at least one atom selected from a carbon atom, a hydrogen atom, an oxygen atom, a nitrogen atom and a sulfur atom, and x is a number of 1 or greater.

Abstract: A composition for hydraulic, lubricating and coupling is disclosed herein, which comprises organopolysiloxane and at least one additive selected from the group consisting of an anti-wear agent which is phosphorus type or sulfur type, a metal deactivator and a corrosion inhibitor. The composition according to the present invention further comprises an antioxidant. The composition according to the present invention can be used at high temperature for a long period, without showing a significant increase in viscosity.

Abstract: A composition for hydraulic, lubricating and coupling is disclosed herein, which comprises organopolysiloxane and as an anti-wear agent at least one compound selected from those of the general formulas (I) to (IV), or an anti-wear agent of at least one compound selected from those of the general formulas (I) to (IV) together with a storage stabilizer. A composition for hydraulic, lubricating and coupling is also disclosed herein, which comprises organopolysiloxane together with a combination of two or more compounds selected from those of the general formulas (V) and (VI) as an anti-wear agent, or a combination of at least one compound selected from those of the general formulas (V) and (VI) as an anti-wear agent and a storage stabilizer. If necessary, the composition according to the present invention further comprises an antioxidant. The composition according to the present invention can be used at high temperature for a long period, without showing a significant increase in viscosity.

Abstract: In the fluid for viscous coupling according to the present invention, organopolysiloxane is used as base oil, and by adding phosphorus type anti-wear agent or by adding the combination of said phosphorus type anti-wear agent with antioxidant or by adding the combination of phosphorus type anti-wear agent with sulfur type anti-wear agent and/or zinc dithiophosphate type anti-wear agent or further by adding antioxidant, it is possible to increase heat-resistant property without changing the viscosity when viscous coupling is in operation and to provide the fluid for viscous coupling with few wear fragment iron quantity and with high durability.