Which water to use
This question matters more than it appears. Half of a ready 50/50 mix is water, meaning half of what goes into the system is chosen by you. The good news is that Zerex Asian Blue is more forgiving here than most.
What the manufacturer says
According to the data sheet, the concentrate should be diluted with clean tap water or demineralised water. It separately notes that the product is hard water compatible.
That is a substantive detail. Many coolants insist strictly on distilled water, because the calcium and magnesium in hard water react with the inhibitors and precipitate. The phosphated formulation in Zerex Asian Blue is more robust in this respect.
And still, what we recommend
If you have the choice, use distilled or demineralised water. It costs a few lari at a pharmacy or parts shop and removes the mineral question entirely. Saving five lari alongside a 250-lari fluid makes no sense.
If distilled water is not to hand, clean tap water is permitted by the manufacturer and will not cause a disaster.
What you must never use:
- Mineral or spring water, because minerals are precisely what we are trying to avoid.
- Well water or irrigation water.
- Tap water, if in your area it runs rusty or cloudy.
Why scale is a problem
Scale deposits as a thin layer on the walls of the coolant passages. That layer is a thermal insulator, which is the exact opposite of what you want. A millimetre of deposit measurably degrades heat transfer.
The worst consequences appear in a hybrid's inverter circuit, where the passages are narrow to begin with. That is why on a hybrid our recommendation for distilled water is more categorical.