Coolant...

[Dr.Kamiya]

So what's wrong with increased coolant concentration? The cooling capacity mostly comes from water, not coolant.

Water has a specific heat of about 4.19J/g-C. Ethylene glycol is only a bit more than half that at 2.36J/g-C. The commonly used 50-50 mix is 3.56J/g-C, but you can see that most of the cooling will be coming from the 50% water mix. As the amount of water in the coolant is reduced, the cooling capacity reduces sharply until you end up closer to the 2.36J/g-C of ethylene glycol.

OTOH a 75% water / 25% ethylene glycol mix will have a specific heat of 3.93J/g-C, which is a lot closer to pure water. We don't really have winter so the anti-freeze properties aren't as needed. We just need the additives in the coolant that prevent galvanic corrosion, and this can be done with as little as 15% anti-freeze.