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A coolant additive is fundamentally designed to reduce the boil-point of the cooling medium in the radiator, hoses, engine and other related parts of the vehicle cooling system. It also contains some form of corrosion inhibitor and may deposit fine particles onto metal surfaces to repair minor damage.
Coolant is available from parts stores either as concentrate OR as a pre-mix. The former should be used as a mix with clean (preferably demineralised) water in proportions stated in your vehicle manual. (Usually between 25% and 50% coolant concentrate to water) Never use 100% coolant instead of a water/coolant mix.
Contrary to information on some websites/forums, do NOT mix red and green coolants because they can create sludge in the cooling system. Also the beneficial long-life properties of the higher-priced OAT orange coolant will be significantly reduced.
Green Coolant contains phosphates and silicates as pH buffers for corrosion protection in an ethylene glycol base. The corrosion inhibitors have a fairly short life, so the coolant needs to be changed about every 50,000 Km.
OAT coolants are based on organic acids and do contain silicates to offer protection for aluminium engines.
Orange coolant is based on 2-ethylhexanoic-acid or 2-EHA and other organic acids. It does contain corrosion inhibitors that form a thin coating on metal components, These typically last up to 5 years or 200,000 Km. Orange coolant may NOT actually be orange. Some brands may be pink, red, blue, yellow or a very dark green so care must be taken because they are NOT generally compatible.
Hybrid coolants may comprise variants of any/all of the above but generally do NOT contain the phosphates that may cause unwanted deposits in modern engines.
Using isopropyl alcohol instead of proprietary antifreeze is definitely NOT recommended. Not only will it be more expensive, it lacks the essential inhibitors.
Graeme Cooper Automotive use PENRITE coolants exclusively. This brand includes ALL of the variants described above and the experts at GCA will know precisely which option best suits your vehicle.