— Understanding Engine Coolants
Engine coolants are critical for maintaining optimal engine temperature, but confusion often arises between terms like antifreeze, coolant, and radiator fluid. Many technicians and fleet managers ask, is antifreeze and coolant the same thing ? In reality, coolant refers to the ready-to-use liquid circulating in the cooling system, while antifreeze is the concentrated glycol-based additive mixed with water to make that coolant. This mixture protects the engine from overheating and freezing by absorbing heat and significantly raising the boiling point of the fluid. By carrying away excess heat and incorporating corrosion inhibitors, engine coolant keeps combustion engines running efficiently under all driving conditions.
What Does Coolant Do in a Car?
Engine coolant (also called radiator fluid) circulates through the engine block and radiator to absorb and carry away excess heat. It is typically a 50/50 mix of water and antifreeze (glycol) plus corrosion inhibitors.
The coolant is pumped through passages in the engine where it picks up heat, and then flows to the radiator to dissipate that heat to the outside air . For instance, the liquid cooling system comprises a water pump, radiator, hoses, and thermostat, which work together to circulate coolant and regulate the engine temperature . In effect, coolant prevents the engine from overheating in hot conditions and from freezing solid in cold weather . It also lubricates components like the water pump and provides corrosion protection, extending engine life .
Understanding Antifreeze: The Core Component of Coolant
Antifreeze is the concentrated chemical (often ethylene glycol or propylene glycol) that is mixed with water to create engine coolant. Its main role is to modify the properties of the coolant mixture.
Specifically, antifreeze lowers the freezing point and raises the boiling point of the fluid, so that the engine stays in its ideal temperature range in all conditions. In cold climates, sufficient antifreeze prevents the fluid from freezing and damaging the engine; in hot conditions, it prevents boiling over. Because pure antifreeze is still corrosive and viscous, it is almost always diluted (commonly 50/50) with water to form the coolant. Antifreeze formulations also include corrosion inhibitors, rust inhibitors and other additives to protect engine components and extend system life.
Difference in Coolant and Antifreeze: Are They the Same?
Despite common usage, antifreeze and engine coolant are not the same product. Coolant refers to the diluted mixture (water plus antifreeze) circulating in the engine, whereas pure antifreeze is the concentrated additive. As one guide explains, “coolant is the product you put into your car, while antifreeze is the active ingredient in coolant”. Another expert notes that “antifreeze is a key
component of engine coolant,” emphasizing that the terms share similarities but are technically different. A 50/50 antifreeze-water coolant typically protects down to about –34°F and raises the
boiling point above 220°F. In short, “all coolants are antifreeze, but not all antifreeze are
coolants”, so be sure to use the product in the correct form (concentrate vs premixed).
Engine Coolant, Radiator Fluid, and Other Terms
You may also hear the coolant mixture referred to by other names. In service manuals and OEM literature, engine coolant and radiator fluid are interchangeable terms for the same thing: the fluid that flows through the radiator and engine to manage temperature. In fact, one source explicitly states that“coolant is also known as radiator fluid,” highlighting that these names all refer to the circulating mixture. Other phrases like radiator coolant or engine antifreeze generally mean the same engine coolant. No matter the terminology, the important point is to use the correct coolant formulation specified for your vehicles’ engines.
Choosing and Maintaining the Right Coolant
Not all coolants are the same. There are different formulations—traditional inorganic acid technology(IAT) coolants (typically green), hybrid organic acid technology (HOAT) coolants (yellow/orange), and organic acid technology (OAT) coolants (red/pink). For example, TERZO Lubricant offers long-life OAT antifreeze designed for extreme conditions (see our coolant products for details). When choosing a coolant, it’s important to match the type to the engine manufacturer’s specification. Use premixed fluids or mix concentrate with distilled water to achieve the correct ratio (often 50/50). Proper maintenance is also key: experts recommend flushing and replacing coolant periodically (every 2–5 years or about 30,000–50,000 miles) to prevent additive depletion and corrosion. Failing to change degraded coolant can allow rust or scale to build up and compromise the cooling system.
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