Phillips 66® Guardol OAT HD Coolant/Antifreeze is an Organic Acid Technology (OAT) that is intended for use and compatible with any OAT extended life heavy duty coolant/antifreeze in any diesel commercial vehicle engine or stationary engine with aluminum and other various engine metals. The advanced formulation is based on a concentrated blend of long-lasting inhibitors designed to provide up to 600,000 miles/12,000 hours* of protection against temperature extremes, corrosion, scale, rust and premature water pump failure. Guardol OAT HD Coolant/Antifreeze is available in both concentrate and prediluted 50/50 formulas.

*TOP OFF: Will maintain extended life protection when added to any OAT extended life antifreeze/coolant.

FLUSH AND FILL: Receive protection for up to 600,000 miles or 12,000 hours with a complete flush and fill using Guardol OAT HD Coolant/Antifreeze.


Features & Benefits

  • Nitrite free, Organic Acid Technology (OAT)
  • Compatible with all heavy duty OAT formulations
  • Requires no initial Supplemental Coolant Additive (SCA) or Extender
  • Complete liner pitting and corrosion protection for aluminum and all other engine metals
  • When used as directed, Guardol OAT HD Coolant/Antifreeze provides long-lasting inhibition and corrosion protection


  • Check engine coolant level frequently and top off with Guardol OAT HD Coolant/Antifreeze when necessary. Guardol OAT HD Coolant/Antifreeze can also be used for flush and fill. To ensure best performance, the system should be drained and flushed thoroughly. A 50/50 mix of Guardol OAT HD Coolant/Antifreeze is recommended to ensure proper freezing/boilover protection. To provide the proper concentration level of inhibitors, never exceed 70%. Always check the specific maintenance and change-out intervals, coolant/antifreeze to water ratio, cooling system capacity, and service instructions recommended for your vehicle.
  • Meets or exceeds the following performance requirements:
  • ASTM D3306, D4985, D6210, D7583
  • TMC RP329, RP338
  • Cummins Bulletin 3666132
  • Cummins CES 14603
  • Navistar
  • Detroit Diesel 93K217
  • Freightliner 48-25878
  • CAT EC-1
  • Volvo 128603
  • SAE J1941
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