Antifreeze Mix Calculator

What to work out

System volume, l

Freezing point wanted, °C

Result

Concentrate, l2.9
Distilled water, l3.1
Concentrate share, %48.3%
Freezes at, °C-35
Boils at, °C109
What mattersMix with distilled water only: tap-water salts leave scale and sediment.

More concentrate is not better

Works out the concentrate and distilled water needed for a coolant with the freezing point you want, and gives the boiling point of the resulting mixture.

The freezing curve of ethylene glycol is not a straight line. Up to about 65 percent the mixture freezes progressively later, the minimum sits near minus 65, and past that the freezing point rises again. Neat concentrate crystallises at around minus 13.

So 'I will pour it in undiluted, it will be safer' is wrong twice over: it holds off frost worse, and glycol carries less heat than water, so the engine cools less well. The working point for a temperate climate is around 50 percent, which is minus 37.

What this calculator shows

The volume of concentrate and water for your cooling system
The final share of glycol and the freezing point it gives
The boiling point — glycol lifts it by roughly a degree per six percent

What to keep in mind

The table is for ethylene glycol; propylene-glycol coolants freeze a few degrees earlier at the same concentration.
Dilute with distilled water only: the hardness salts in tap water leave scale inside the cooling jacket.

FAQs

What ratio do I mix antifreeze concentrate at?

One to one gives about minus 37 and suits most temperate climates. Minus 25 needs only 40 percent concentrate; minus 50 needs about 60.

Can I pour concentrate in neat?

No. Pure ethylene glycol freezes at around minus 13 and carries heat away worse than a mixture with water.

What water should I use?

Distilled only. Tap water carries salts that settle as scale inside the cooling jacket and the radiator.

Can I mix different coloured coolants?

Colour means nothing; the additive package does. G11, G12 and G13 use different chemistry, and mixing them drops the additives out of solution.

Worked example

Six litres down to minus thirty-five

Input: 6 l system, target −35 °C

Output: 2.90 l concentrate and 3.10 l water, 48% glycol

Note: Almost half and half — which is the standard factory ratio. That mixture starts boiling near 109 degrees even without system pressure, and the cap adds more margin on top.

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Antifreeze Mix Calculator

Result

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