How Stuff Works

Anti-Freeze

Rather surprisingly, anti-freeze didn’t come to the mass motoring market until the 1920s, following military usage and a whole heap of home- or locally-brewed alcoholbased concoctions.

Because water was known to be such a magnificent conductor of heat, it became the coolant liquid of choice within internal combustion engines. This was fine for vehicles used in climates where freezing temperatures were not a problem, but for everywhere else, including these fair lands, what was needed was an additive to prevent the water’s negative thermal expansion.

Negative thermal expansion? Ice takes up more space than the water from which it is formed so can damage any relatively rigid container – the engine, in this case – in which it sits. This damage could be catastrophic, with split blocks and cylinder heads being common results of freezing.

Most classic engines came fitted with core plugs as expansion failure points, to attempt to avoid their destruction, should the coolant contained therein have reached its solid state.

There, in a nutshell, was the reason why anti-freeze became such a hot topic among the burgeoning motoring public.

The earliest anti-freeze added to plain water was methanol (methyl alcohol). However, methanol had a relatively low boiling point, lowering the point at which the coolant mixture became a gas and so causing problems, especially with early, unpressurised cooling systems.

To address this and other problems, ethylene glycol was developed; with its higher boiling point, low freezing point, low viscosity, excellent thermal conductivity and stability across the range of temperatures within which it was expected to work, made it an attractive proposition and it remained the cooling system tipple of choice – until it fell out of favour due to its environmental toxicity.

At around the same time, cooling systems became pressurised, preventing the coolant water from achieving its gaseous state at a mere 100 degrees Celsius, keeping it as a liquid way above this temperature.

Thus, engine coolant was able to work at a temperature range way beyond that of plain water, but there were still problems.

Water alone, when circulated through the cooling system – the latter containing components manufactured using many differing metals – promoted galvanic corrosion between them. Anti-freeze alone could not prevent this, so products began to be formulated with corrosion-inhibiting ingredients included.

Anti-freeze, therefore, became an increasingly sophisticated chemical cocktail, featuring lubricants for water pump seals, as well as additives to help keep rubber items supple.

The environmental toxicity of ethylene glycol proved to be its downfall and so other formulations took its place, including propylene glycol and, even more recently, antifreezes featuring ‘organic acid technology’ (OAT), the latter with its claimed extended service life.

However, it’s been claimed that modern anti-freezes featuring OAT have caused damage to gaskets within older engines and so are not recommended, unless the manufacturer specifically refers to the safety of the product within older machines. Generally, these newer anti-freezes can be identified by their red or orange colour.

Like all good stuff, ethylene glycol-based anti-freeze remains available, and with excellent corrosion inhibitors included in the formulation. classic-oils.net/classic-Oils-2-yearBlue-anti-Freeze