Time to get out car antifreeze

Winter is on us and vehicles that have to sleep outside at night are feeling its icy grip.

Time to make sure the antifreeze mixture in the cooling system is up to scratch.

Early in the last century it was found that ethylene glycol, a chemical compound derived from petroleum, lowers the freezing point when mixed with water. So since 1937, when widespread industrial production started, it has been a mainstay of antifreeze formulations.

How much it lowers the freezing point when mixed with water, depends on the concentration strength.

A graph of freezing point vs concentration strength shows that as the percentage of ethylene glycol in the mixture increases, the freezing point drops.

But this only happens until the concentration strength reaches 70% (that is, 70% ethylene glycol mixed with 30% water), after which it rises again if you add more ethylene glycol.

In concentrated form most automotive antifreezes consist of about 95% ethylene glycol, the other 5% being made up of corrosion inhibitors, anti-foamants and water. It is in this additive package that the difference between various brands of antifreeze lies.

It is recommended that the coolant in a car's engine be drained and replaced with a fresh antifreezewater mixture every two years or 40000km to refresh the additives that are slowly depleted.

Just make sure, if the car is still under guarantee and that the product is approved by the car manufacturer. And take care, before refilling, to flush the entire cooling system, not just the radiator, to get all the old antifreeze out.

At the same time it's advisable to use the pre-mixed form of the long-life product, because that would have been diluted in the correct ratio with demineralised water to minimise scale deposits inside the engine.