What is Engine Coolant and What Does it Do?

An engine coolant is a heat transfer fluid designed to remove excess heat from an internal combustion engine. An operating engine typically converts only one third of the energy derived through the combustion of fuel into work that moves the vehicle. The other two thirds is converted into heat, of which one third goes out with the exhaust. This leaves the remaining third in the engine block, necessitating the need for a coolant to adsorb this heat, transport it to the radiator and dissipate it into the environment. Through the removal of this heat by the coolant fluid, the engine is able to operate in an efficient manner. Therefore engine coolant is a generic term used to describe fluids that remove heat from an engine, in effect ‘cooling’ the engine.

Not all fluids are efficient heat transfer materials, when employed in the extreme setting as found in a combustion engine. Selection of the proper fluid is influenced by the environment in which the engine is used and the interaction of the fluid with the materials that comprise the engine. Some environments such as those found in northern latitudes may expose an engine to periods of extreme cold, requiring the fluid remain liquid in order to function properly. In effect, the heat transfer fluid must be impervious to freezing or expressed in other terms, it must possess “anti-freezing” characteristics. It is for this reason that engine coolant is sometimes referred to as antifreeze. Antifreeze is a more specific term used to describe products that provide protection against freezing. Many people use the terms coolant and antifreeze interchangeably. For the purpose of consistency, we will use the term coolant when describing an engine heat transfer fluid.

Conversely, during engine operation the fluid must possess the ability to remain a fluid as it is heated during operation. It must resist the tendency to boil and form vapours as this reduces its ability to transfer heat. An efficient heat transfer fluid for use in combustion engines will have a low freeze point and an elevated boil point ensuring its capacity to perform in all situations encountered in the environment.