coolant

Coolant is a fluid used to remove heat from systems that generate significant heat during operation, and to prevent freezing and excessive boiling. It often contains additives to inhibit corrosion, suppress foaming, and protect seals and metals.

In automotive engines, coolant is usually a glycol–water mixture sold as a 50/50 blend and may use ethylene glycol or propylene glycol. Inhibitors such as silicates, phosphates, or organic acids protect the cooling channels and pump from corrosion. The system includes the radiator, water pump, thermostat, hoses, and expansion tank. Manufacturers specify IAT, HOAT, or OAT types, and mixing incompatible formulations reduces protection. Conventional coolants commonly require 2–3 years of service; extended-life products can last 5 years or more, depending on the product and vehicle manual.

Outside automobiles, coolants are used in process cooling, power generation, and electronics cooling. In refrigeration and HVAC, the term refrigerant refers to a working fluid in a closed cycle designed for phase changes and large temperature shifts, rather than just freezing point depression. Safety concerns include ethylene glycol’s toxicity, while propylene glycol is less toxic. Proper disposal or recycling of spent coolant is required by regulations to prevent environmental harm and exposure.