Fleetguard coolant concentrate is a highly concentrated liquid additive used in heavy-duty engine cooling systems to provide freeze protection, prevent boiling, inhibit corrosion and scaling, and protect against cavitation. It must be diluted with water (typically a 50/50 ratio) to create a functional coolant. Fleetguard offers various formulations, such as ES Compleat, which are designed for extended life and optimal protection in diesel and gas engines, using technologies like ester-based chemistry.