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A Guide To Antifreeze/Engine Coolant

Overheating can cause major damage to your vehicle's engine block and to its delicate components. However, a high quality antifreeze/coolant can prevent this from happening. We’ve composed a guide to what antifreeze/coolant is, what it’s made of, and some of our favourite types for your car or motorcycle.

What is antifreeze/engine coolant?

Antifreeze is an additive that you add to your engine to reduce the freezing point and increase the boiling point of the liquid inside the radiator. It helps to keep the liquid in your engine at a stable temperature – preventing your engine from freezing up or overheating.

Generally, antifreeze and engine coolant refer to the same thing. However, regular water can also be referred to as coolant, as it’s effective at preventing your engine from overheating. It’s worth noting, though, that using water as engine coolant won’t protect against sub-freezing temperatures or corrosion inside the engine. Antifreeze, on the other hand, can protect from both of these things.

How does antifreeze work?

Most commercial antifreeze formulations include a glycol (to suppress the freezing point and raise the boiling point), corrosion inhibiting compounds and a coloured dye (commonly orange, green, red, or fluorescent blue) to aid in identification. A 1:1 dilution with water is usually used, resulting in a freezing point in the range of -37 °C to -42 °C, depending on the formulation.

There are two basic types of coolant available dependent on the corrosion inhibitors used:

1. Inorganic additive technology (IAT)

2. Organic additive technology (OAT)

Inorganic Additive Technology

This is the traditional coolant based on inorganic additives and is called inorganic additive technology (IAT). It is a tried and proven chemistry that provides a fast-acting protective film. The additives deplete and the coolant needs to be drained and replenished every couple of years. This type can be used on all mixed metal engines with components including steel, cast iron, copper, brass, aluminium and solder without any detrimental effects.

Organic Acid Technology

The newer OAT coolants work differently than the older silicate based IAT coolants. Aluminium and ferrous metals form a surface-layer of corrosion in the presence of moisture, even with the little bit of moisture in the air. OAT coolants prevent this metal-oxide layer that protects the surface against this corrosion.

Inherent with their design, the OAT coolants last longer than the older traditional IAT coolants. This category of antifreeze cannot be used in systems containing yellow metals.

Why are coolants different colours?

Coolants/antifreezes are coloured so you can visually see when you add them; colour intensity can be an indication of over dilution. Keep in mind that the different colours that antifreeze and coolant come in don’t really mean anything – the manufacturer can dye the product any colour they want. The colour is no guide to the actual type of antifreeze and the label should be read before use.

What is best for performance use?

It is always best to use the engine manufacturer's advice. If your engine contains yellow metals (copper and brass as in older vehicles) then the long-life products based on organic technology should be avoided. As a general rule, most modern engines require the long-life organic antifreezes.

Is there any advantage to using concentrate over pre-mixed coolants?

None - other than the user may want to use the pre-mixed product due to ease of handling or cost and vice versa.

Can concentrate and pre-mixed coolants be mixed?

A simple answer is that, generally, you can mix concentrate and pre-mixed coolants. However, don’t mix IAT and OAT antifreeze together. When mixed, they can form a sludgy gel that can clog up your cooling system. In more severe cases, this can cause problems in your water pump and heater cores, to mention a few.

With thanks to Martyn Mann - Technical Director, Millers Oils for his contribution to this article.

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