I have been using a cool coat on my Black Dog for a few years now when it is really hot.
Her coat underneath the cool coat feels cool to the touch and she certainly does not pant as much with it on.
This is supplemented by letting her have a dip in the water or hosing her down.
It seems to work.
This is not the first black dog I have had.
Lighter shades don't seem to suffer so much.
Black dogs do suffer more from direct sun.
You are obviously monitoring your use of a cool coat, most owners do not and just assume it is doing good, but water gets warm very quickly and the coat traps heat in the dog.
It is internal organs getting too hot that does for dogs, they have no idea until it is too late, they have a furry coat for a reason and the one thing they struggle with is dissipating internal heat, they do not sweat, a coat does not help with this, unless you have a bald dog I very much doubt your vet would recommend any type of coat. They are very adept at keeping themselves warm not so good at keeping cool.
They have lived for years without them, most love rolling on snow or frosty ground, all mine have over the years, coats are a human thing that humans have transferred to dogs, in most cases they do not help at all.
They associate you picking up the coat and putting it on with going out, that is all, same as they do when putting your coat on.
