50/50 is whats used here in Minnesota too. Our summers are very hot a nd humid. Trust me, a 75% coolent mixture would kill a car with our summers. To be honest I don't know if i'd trust that car. Even with a 50/50 mix of Dex my car gets up to 225* frequently in the heat with a 180* T-stat. I don't even want to think about how hot that car was getting.