Morris Lubricants’ rundown on antifreeze coolants

Morris Lubricants’ rundown on antifreeze coolants

Morris Lubricants gives readers the rundown on antifreeze coolants.

For anyone running a vehicle with an internal combustion engine, an antifreeze coolant is essential, but it does a lot more than the name would suggest.

Operating at high temperatures…

The best cooling medium is water. However, when the engine reaches running temperature it will exceed the boiling point of water, 100˚C. If the water boils away, catastrophic damage can occur in the engine. To combat this, antifreeze coolants feature the addition of monoethylene glycol, which elevates the solution’s boiling point to around 108˚C.

…and low temperatures

If the engine has been at rest and the ambient temperature falls below 0˚C, water freezes, and the ice formed expands. This is a big issue in the engine cooling system as there is nowhere for the expansion to go. As the water freezes, high internal pressures are generated that can crack heads, cause splits in cylinder liners, make hoses leak, fracture radiators and break water pumps. By incorporating monoethylene glycol to the water it reduces the freezing point, potentially driving it down to -35˚C.


Another important function of an antifreeze coolant is to prevent any metallic components from rusting or corroding, such as the engine block, water pumps or gaskets. It is therefore essential that the antifreeze coolant uses the correct chemistry in its formulation to stop this.

Rusting and corrosion are prevented by an inhibitor package, which is a combination of chemical compounds chosen to optimise its ability to protect the cooling system. This chemistry is referred to as either inorganic or organic acid technology.

Inorganic chemistry is extremely active and will seek out all materials in the cooling system, whether susceptible to rusting or corrosion or not. This constant level of activity results in it becoming depleted after around two years. At this point it should be drained and changed.

Organic acid technology only targets materials where rusting or corrosion is starting to take place. This chemistry is selective and does not become depleted as quickly and will work for up to five years. Some manufacturers may require a combination of these technologies and ‘hybrid’ antifreezes are available for specific engine designs.

And there’s more!

Additional chemistry may also be added to the formulation of antifreeze coolants such as antioxidants to stop corrosive acid formation as well as additional compounds to prevent hard water deposits and extra pH buffering agents to maintain an optimum pH level (around 8). The formation of foam can also inhibit the properties of the antifreeze coolant, therefore an antifoaming agent may be added to the formulation to prevent foam developing within the cooling system.


The language of antifreeze coolants tends to be based on their colour. But be aware, colour is not an indication of quality or performance and is purely cosmetic having no impact on how the antifreeze coolant performs in terms of engine protection.

Choosing the correct antifreeze coolant

As engine designs become more complex and engines are manufactured from different metals and composite materials, the correct antifreeze coolant must be used. If not, the antifreeze coolant will damage the engine and reduce its efficiency. When choosing the correct antifreeze coolant, you need to make sure it meets the specifications set by the engine manufacturer.

Antifreeze coolants perform in the engine all year round and do not just cover the winter months. Selecting the correct antifreeze coolant is vital and choosing a product based on colour should be avoided. Best practice is to select the antifreeze coolant based on the engine manufacturer’s specification. If there is any doubt as to which antifreeze coolant is required, check with the engine manufacturer, seek independent technical advice, or use online tools such as

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