Coolant Mix Calculator

How much coolant to drain and replace with concentrate to reach a target mix.

Freeze protection (ethylene glycol, approximate)

ConcentrationFreeze protection
30%about −15 °C (5 °F)
40%about −24 °C (−12 °F)
50%about −37 °C (−34 °F)
60%about −52 °C (−62 °F)

Most manufacturers specify 50/50. Going above about 60–70% reduces both freeze protection and heat transfer. Always use the coolant type the manufacturer specifies (OAT, HOAT, P-HOAT and so on) and check the concentration with a refractometer. Never open a hot cooling system.

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