[SwissXC90]

Originally Posted by Semnoz

Due to a recent issue with a leaking coolant hose (very short hose hidden away next to the EGR), I had to top up the coolant fluid a few times; sometimes water (if that's all I had) and sometimes orange antifreeze (when I've stopped at a garage).

And given the lack of history before I got the car, I have no idea what the antifreeze/water ratio is.

Once I've replaced the host, is there any harm in me just topping it up with 100% antifreeze ?

In other words, is there any risk in having, say, 2/3rds antifreeze and 1/3rd water ?

Extremely important if your vehicle will be in regions of the world where you may be approaching the lower limit of your antifreeze.

Where I am in Switzerland, we have areas that can reach -20°C in Winter.
If your car is parked outside in one of these areas, you need to be really sure your coolant is protected down to at least -20°C. Otherwise your engine is damaged when the coolant freezes and expands, and that is not good at all.

But if you have coolant made for -20°C, and you dilute it a little bit, and your area of the world never gets colder than 0°C, then you are likely to be OK as you have 20° of reserve to play with.