Back in the day of cool running engines, iron heads and copper radiators we used to just put a garden hose to the radiator and fill it up. That will quickly destroy an engine now. It is critical you use a coolant with the proper chemistry for your car. The water pump and the cooling passages in the interior of the engine will suffer with any substitute, and replacing many modern water pumps can be shockingly expensive.
Living in a hot climate makes the proper coolant even more critical. Water boils at 246F with a 15 psi pressure cap; 50% glycol boils at 265F and 70% glycol boils at 276F under the same pressure.
In my experience the most common cause of premature engine death is timing belt neglect; the second most common cause is cooling system neglect. Using the correct coolant, mixed if necessary with purified water (no tap water ever in car cooling systems!), can more than double the life of the engine in any climate. I will not even consider buying a used car that does not have the proper coolant or has any trace of rust in the cooling system... I learned about that the hard way.
Napa Kool is fine. Buy the test strips so you can make sure you've got and maintain the proper level of anti corrosion additives. Flag michael is dead on about the temps...your radiator cap is the major source of boilover protection, if it gets hotter than 246*, who cares if it doesn't boil until 270*...you are already causing potentially serious damage to the engine at that point.
Ignoring the boiling point, water is a better coolant than antifreeze in any case, so an engine with straight water (with corrosion additives) will run cooler than an engine with ANY antifreeze in it. Obviously as percent antifreeze increases, the coolant will be less efficient at removing heat from the engine.
Sounds wrong, but trust me...the antifreeze manufacturers have been doing a GOOD job making people think you have to have antifreeze. You do, only if freezing is an issue for you. No race tracks around here allow antifreeze, so they use water and it works fine.
I would use manufactures recommended coolant. You may not need freeze protection but it will cool better than plain water with anti-rust.
One 12 can of water-soluable water-pump lubricant and 100% distilled water will COOL the engine more efficiently than any percentage of high viscosity antifreeze IF it never freezes where you live. Go to the Stewart water-pump website and it will tell you the same thing.
Prestone - Radiator Super Anti-Rust
will be the best option for you.
HI all anit-freeze has anti-rust .. if you don't use antifreeze then you should be able to buy a rust inhibitor at any parts store..
