Coolant colour

Then why must you not mix?

Because although colour does not determine chemistry, the chemistries genuinely do differ, and their inhibitor packages frequently neutralise one another.

Mixing a phosphated Japanese fluid with a silicated European one, for instance, can produce a precipitate that resembles neither and performs the function of neither. The result is sludge, blocked passages and the loss of both protection packages.

Honda's manual states this directly, that blue Type 2 must not be mixed with green Type 1, pink, orange or yellow.

Colour is still useful, but for a different reason

Colour is information. At a glance it tells you which family of fluid is probably in the system, which is useful when you do not know the car's history.

It is also a leak-diagnosis tool: a blue puddle in the car park tells you immediately that this is coolant and not oil or brake fluid.

That is why our advice is what it is: refill with the colour the system already holds. Pink takes Valvoline Zerex Asian Red, green takes Asian Green, and blue takes Asian Blue. Switching colours inside this family causes no chemical problem, but you lose the information.

A short orientation

This is a general orientation, not a rule. Always defer to the manual.

• Blue. Often an Asian HOAT with phosphate: Honda Type 2, Nissan S-LLC, Subaru Super Coolant.
• Green. Either an older IAT type or the green variant of an Asian HOAT: Hyundai and Kia MS591-08, Mazda FL22, Mitsubishi, older Nissan LLC. Be especially careful here, since two entirely different chemistries look identical.
• Pink and red. Often Toyota SLLC or an Asian red HOAT.
• Orange. Often a Dex-Cool style OAT, usually containing 2-EHA.
• Yellow. Often “universal” fluids whose composition varies widely.