Coolant concentration & top-up calculator
Concentration % = refractometer reading (°Brix) × the coolant's refractometer factor. The factor is on the coolant's data sheet; it is 1.0 only for a coolant that reads direct, and many read well above it. A sump of 200 L holding 170 L at 4 % needs 5.2 L of concentrate in 24.8 L of water (a 17.3 % premix) to end full at 6 %.
Enter the reading, the factor, the target and the sump's volumes, and the calculator gives the concentrate and water to add, what to draw off first when there is no room, and the premix ratio.
Concentration
Sump
- Concentration now c
- Add concentrate X
- Add water W
- Draw off first D
- As a premix
- Premix ratio, concentrate : water
- 1 : 4.8
How it’s calculated
c = reading × factor, the factor from the coolant's data sheet (1.0 is only a default). With D drawn off, the sump ends full at the target when (V − D)·c + X = Vf·ct and X + W = Vf − V + D. A ratio of 1 part concentrate to n of water is 100/(n + 1) %; one part in n of the mix is 100/n %.
Mix ratios
| Ratio 1 : n | As 1 part to n of water | As 1 part in n of the mix |
|---|---|---|
| 1 : 5 | 16.67 % | 20.00 % |
| 1 : 10 | 9.09 % | 10.00 % |
| 1 : 12 | 7.69 % | 8.33 % |
| 1 : 15 | 6.25 % | 6.67 % |
| 1 : 20 | 4.76 % | 5.00 % |
| 1 : 25 | 3.85 % | 4.00 % |
| 1 : 30 | 3.23 % | 3.33 % |
| 1 : 40 | 2.44 % | 2.50 % |
| 1 : 50 | 1.96 % | 2.00 % |
How do you measure coolant concentration?
With a refractometer: zero it on water (the water you mix with, if you can), put a drop of clean coolant from the working sump on the prism and read the Brix scale. The Brix scale is set for sugar in water, so the reading is the concentration only when the coolant's factor is 1.0; otherwise multiply by the factor on its data sheet.
How much concentrate do I add?
Balance the concentrate. If the sump holds Vf full and has V in it at c, and should end full at ct, the concentrate to add is Vf·ct − V·c and the rest of the room is water. When the sump is too full for that (too lean with no room for enough concentrate, or too rich with no room for enough water), draw some off first; drawing off more than the least leaves room to top up with a premix. Coolant makers advise topping up with a premix rather than pouring in neat concentrate or plain water.
Is 1:20 the same as 5 %?
Not quite. One part concentrate to 20 parts water is 1/21 of the mix, 4.76 %. Some makers' charts write 1:20 for 5 %, meaning one part in 20 of the mix. The table gives both readings so you can match the chart you are reading.