The XT660 cooling system requires an ethylene glycol based coolant without silicate, phosphate or boric corrosion inhibitors. This type of coolant is often branded as "organic" and falls into the OAT (organic acid technology) category. Whichever brand you choose look for one that says "OAT" or "organic" on the label and is ethylene glycol based. They often say they are silicate and boric free.

These days (now most cars on the road have aluminium blocks and heads like motorcycles) there is generally no difference between car and motorcycle OAT coolants. Going back ten years or so a lot of car coolants contained silicates, which were added to the mix to scour the rust deposits from the waterways of iron blocks and copper oxide from brass cored radiators. The waterways in iron blocks (and heads) and the cores of brass radiators are substantially bigger than those in aluminium blocks, heads and radiators so are less prone to getting blocked by these silicates flowing round the system, so you don't see silicates so much anymore. The other problem with silicates for the motorcyclist is that they can destroy the mechanical seal in the water pumps of bike engines due to their abrasive nature.

In a nutshell, a car coolant will be fine as long as it is OAT ethylene glycol based type 2 coolant without silicates, boric acid or phosphates, in other words it is "suitable for aluminium engines".

Save your money and buy a car coolant if you like, but ALWAYS read the label carefully!

Note: It is not recommended to mix IAT (inorganic acid technology), or HOAT (hybird organic acid technology) coolants with OAT types because they contain silicates, phosphates and boric acid which effect the life of the coolant and can cause deposits to build up. As a precaution, in an ideal world, it is always best to flush the cooling system through with clean (preferably de-ionised) water or a flushing agent before replacing the coolant.

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