This specification covers the requirements for a fully-formulated propylene glycol-base coolant for cooling systems of heavy-duty engines. When concentrates are used at 40 to 60% propylene-glycol concentration by volume in water of suitable quality, (see Appendix X1), or when prediluted propylene-glycol base engine coolants (50% volume, % minimum) are used without further dilution it will function effectively during both winter and summer to provide protection against corrosion, cavitation, freezing, and boiling.