Coolant mixtures

Cooling and heating systems / Coolant mixtures

1 In cold climates, antifreeze is needed for two reasons. In extreme cases, if the coolant in the engine freezes solid it could crack the cylinder block or head. But also in cold weather, with the circulation restricted by the thermostat, and any warm water that is getting to the radiator being at the top, the bottom of the radiator could freeze, and so block circulation completely, making the coolant trapped in the engine boil.

2 The antifreeze should be mixed in the proportions advocated by the makers, according to the climate. There are two levels of protection. The first cuts risk of damage, as the antifreeze goes mushy before freezing.

The second, valid all year round, is the corrosion protection it offers - see below. The normal proportion in a temperate climate to provide maximum protection against freezing and corrosion is 50% antifreeze and 50% water.

3 Use only ethylene glycol based antifreeze and preferably soft water.

4 Antifreeze should be left in through the summer. It has an important secondary function, to act as an inhibitor against corrosion. In the cooling system are many different metals, in particular the aluminium of the cylinder head. In contact with the coolant this sets up electrolytic corrosion, accentuated by any dirt in the system. This corrosion can be catastrophically fast.

5 After about two years, the effectiveness of the antifreeze’s inhibitor is used up. It must then be discarded, and the system refilled with new coolant.

6 In warm climates free from frost, an inhibitor should be used. Again, a reputable make giving full protection must be chosen and renewed every two years. Inhibitors with dyes are useful for finding leaks, and on some makes the dye shows when the inhibiting ability is finished.