Antifreeze for Subaru Outback
In Georgia an Outback is used in ways it rarely is elsewhere: long climbs, rough roads, a full cabin and 35 °C summers. All of that puts more load on the cooling system than the factory service interval assumes.
Photographs come from the manufacturer's official materials.
Cooling system volume (litres) roughly six to eight litres
Gradients, load and boiling point
On a long climb with a loaded car the engine sheds far more heat than on level ground. That is exactly when the fluid's boiling point starts to matter.
At 50/50 Zerex Asian Blue boils at 128 °C with a standard 15 psi cap, and at 60/40 it boils at 133 °C. Plain water boils at 100 °C. The difference is precisely the margin you need on a gradient.
If you drive to the mountains in winter
A 50/50 mix protects to −36 °C, which is more than enough for lowland Georgia. If the car winters in the mountains, 60/40 gives −48 °C.
One important detail as well: going beyond 70 per cent concentrate makes protection worse. Neat antifreeze carries heat poorly compared with water and freezes at a higher temperature than a 70 per cent mix. More is not better here.