An Introduction to Coolant Technology

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. It also serves to prevent freezing and most importantly protection from corrosion. 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 to 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. However not all engine coolants need to provide freeze protection.  This is especially true when equipment is used in tropical climates.  In this type of climate you will always need an engine coolant but you may not need the coolant to have freeze protection. 
Consequently water based coolants are often used in these regions.  So in effect, the type of coolant fluid used depends on both the application and the geography/climate in which it is used.  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 may require a low freeze point as well as an elevated boil point ensuring its capacity to perform in all situations encountered in the environment.  Such characteristics are exhibited when glycols are combined with water and for this reason form the basis for all engine coolants.
The two main glycols that are used as engine coolants are: ethylene glycol and propylene glycol. Both can be used in automotive or heavy-duty engine coolants or glycol-based heat transfer fluids, although it is generally accepted that ethylene glycol based fluids when used as directed offer the greatest cost-effective performance advantage.  Propylene glycol based engine coolants or low temperature heat transfer fluids tend to be used in locations where a low toxicity product is required and due to the toxicity of ethylene glycol it cannot be used.
Other base fluids are coming available in the engine coolant market such is 1, 3 propandiol otherwise known as PDO and Glycerin.  However, since the majority of the Global engine coolant market uses either glycols or water we will focus on the use of these materials when discussing engine coolants and heat transfer fluids. 
Engine coolants perform several functions in addition to providing freeze and boil protection. Coolants must also contain additives that inhibit corrosion and scale formation in the engine’s cooling system. Modern engine coolants use a mixture of glycol and water or just de-ionized water with corrosion inhibitor chemicals and dyes included to complete the package.
Such a combination results in a product that provides the following benefits:
  • Effective heat transfer
  • Prevention of cooling system corrosion
  • Effective boiling point
  • Freeze point depression where or if required
  • Chemical stability
  • Safe for use as directed
An easy way to think of engine coolant is consider what it’s made of specifically three main items namely glycol, de-ionized water and corrosion inhibitors as shown below:
Ethylene Glycol or Propylene glycol + Deionized Water + Corrosion Inhibitors = Engine Coolant
The differences between engine coolants are primarily dictated by the quality of the glycol and water used and just as important if not more important are the corrosion inhibitors used. Each corrosion inhibitor technology system is designed for a specific or broad application, dependent on the coolant application and environment in which it is to function.