One thing about using any 50/50 mix of antifreeze is it should be changed every 2-3 years or so. I know lots of people who do change theirs but they never empty the block. If you don't totally empty the whole system its like changing oil and leaving the old filter on. Electroylsis is a big factor in motors with different metals, like aluminum heads and steel block. As the coolant get solder , it also gets more acidic and can turn the radiator into a very weak battery. I've seen the insides of radiator being eaten up by this.