Antifreeze

What does it do and which should you use?

Antifreeze is a concentrated product, normally based on glycol and containing inhibitors

Antifreeze is a concentrated product, normally based on glycol and containing inhibitors.

Making sure that you've got the correct anti-freeze in the right concentration is critical to the health and well-being of your engine.

The coolant capacity of modern systems is smaller and the operating temperatures and pressures higher, while greater use of lightweight materials such as aluminium increases the risk of corrosion.

As a rule of thumb, only about 28% of the thermal energy released by burning fuel in the engine is available for driving the car.

  • About 7% is used to overcome friction in the engine, drive train, tyres etc.
  • Another 35% disappears out of the exhaust, and
  • The remaining 30% has to be removed by the coolant or the engine block would go into melt down.

Engines are constructed from several different metals and it's important to prevent corrosion and scale build up in the cooling system at normal operating temperatures. Around 60% of engine failures can be attributed to cooling system problems.

Antifreeze is multi-functional and vital to the correct operation of the engine. A modern coolant/antifreeze needs the following features:

  • Corrosion prevention
  • Excellent heat transfer
  • Protection from freezing
  • Prevention of scale build up
  • Compatibility with hard water
  • Stability at high temperature
  • Compatibility with plastics and elastomers used in the engine
  • Low foaming
Coolant expansion tank

Coolant expansion tank

Since around 1930 the necessary freeze protection and heat transfer has been provided by mixtures of water and ethylene glycol. This is available in large quantities from the petrochemical industry and has the added advantage of raising the boiling point of the mixture.

More recently propylene glycol has been introduced as a less hazardous alternative to ethylene glycol although this is much more expensive and some manufacturers have been reluctant to use it.

The important recent technical advances have been in the field of corrosion prevention, hard water compatibility and control of scale build up. Engine design has changed to improve fuel efficiency and lower emissions as well as reducing weight and costs. These demands have made engine operating conditions even more severe, so that much more is required from the cooling system.

The coolant/antifreeze used at first fill is chosen by the vehicle manufacturer as the most suitable. Subsequent service top ups or renewals should use a product meeting the original specification so the vehicle warranty is not affected.

Beyond the warranty period, it is still best to follow the vehicle manufacturer's recommendation, however the coolant/antifreeze used should at least meet minimum specifications such as BS6580:2010 or ASTM D 3306. These are national standards that provide a basic level of performance for cars and light vans.

The concentrate is diluted with water prior to use and to ensure adequate cooling system protection a concentration of between 40% and 50% (by volume) is recommended. It's important to remember that vehicle cooling systems are sealed and, under normal circumstances, should not need topping up. If the coolant level in the radiator expansion tank drops, the cooling system should be checked fully.

Developments in coolants have led to the introduction of Organic Acid Technology (OAT). The corrosion inhibitors in OAT products last much longer in service than those in traditional antifreeze and are usually only changed every 5 years.

In spite of improvements in the quality and life expectancy of the products there are many older vehicles which still use traditional antifreezes and these must be renewed every 20,000 mile or 2 years. These coolants are cheaper than the longer life technologies and, although they do not achieve the same corrosion protection performance at the higher temperatures generated in modern engine cooling systems, they should at least meet recognised national standards e.g. BS6580:2010 or ASTM D3306.

Water quality

Although tremendous progress has been made in improving the performance of modern day antifreeze/coolants there is still one factor that can reduce their effectiveness – the quality of the water used for dilution! High levels of calcium and magnesium in tap water, that cause furring of kettle heater elements, can also lead to deposits and scale build up in the engine cooling system. If you are in a hard water area it is advisable to use distilled or deionised water in the cooling system rather than tap water.

(updated 31 January 2012)