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Diamond Class® Heat Transfer Fluids


Phillips 66® Diamond Class Heat Transfer Fluids are premium quality fluids specifically developed for use in liquid-phase heat transfer systems. They are available in two different formulations, designated “O/S” for use in open systems and “C/S” for use in closed systems.

Features & Benefits

  • Outstanding performance in closed or open systems
  • Outstanding thermal stability to minimize deposits
  • Long service life
  • Less waste oil disposal
  • Reduced operating costs


  • Diamond Class Heat Transfer Fluid O/S is optimized for use in pressure-relieved, forced circulation, liquid-phase heat transfer systems where there is the possibility of contact between the heat transfer fluid and air in the system. The O/S fluids are recommended for use in systems operating with continuous bulk oil temperatures up to 550°F (290°C).
  • Diamond Class Heat Transfer Fluid C/S is optimized for use in closed, liquid-phase, forced circulation heat transfer systems equipped with expansion tanks and pressure relief valves. Preventative measures should be taken to minimize oil oxidation by eliminating air from the system prior to bringing the oil up to operating temperature. The use of an inert gas, such as nitrogen, under positive pressure in the expansion tank is recommended at all times during operation. Under no circumstances should the hot oil come into contact with air. C/S 32 is recommended for use in systems operating with continuous bulk oil temperatures up to 620°F (327°C).
  • Skin film temperature can be estimated at 50°F to 75°F above bulk oil temperature in properly designed and operating systems. If skin film temperatures rise higher than this, the service life of the oil may be shortened. Additionally sludge and coke may be deposited resulting in reduced efficiency of the system.
  • Some common applications include:
  • Liquid-phase heat transfer systems*
  • Heat transfer medium for industrial manufacturing processes
  • Heat transfer equipment used in the manufacture of resins and coatings
  • Asphalt heating
  • Die casting
  • Plastic injection molding and extrusion
  • Wax coating equipment

* Caution: These fluids are not to be used in “vapor-phase” heat transfer units, nor should they come into contact with water, which can cause steam and pressure to build up in the system and create the potential for an explosion. Also, under no circumstances should the bulk oil be exposed to continuous high temperatures without the presence of an expansion tank, as the fluid will degrade quickly.