If your not in a freezing climate you can use just water and that is the best. Theres no need for anitfreeze/coolant if its not gonna freeze. Engine ice is good too Ive allways used what ever the dealer had at the time.
If your low on coolant you can add distilled water, tap water isn't real good for the inside of the radiator....
I agree with the above poster who suggested Engine Ice its good stuff, just flush out the old stuff with distilled water before changing over because your NOT suppose to mix Engine Ice with regular antifreeze..
Ok so what will tap water do? I do geothermal heating and a/c systems and I know that the water is the best thing to use since it carries more btus per gallon than antifreeze. The stuff we use on our systems is a propylene glycol mix with water which is very close to the engine ice but I'm sure that has more additves in it.
Tap water has a lot of impurities that can gum up your cooling system. Distilled water is water that is converted to steam, then back to liquid to remove all those impurities, keeping everything clean and free flowing.
Yes water works great for heat transfer, but it's not always the goal to make it run as cool as possible. You want the bike to run at an efficient operating temperature. In warmer climates, as you've said, this is not an issue with water. Anti-freeze also provides protection from corrosion and electrolysis which water does not.
Tap water is full of stuff that isn't water; organic and non organic chemicals, minerals, metals, microorganisms like algae, and other contaminants will cause corrosion and could plug up the radiator itself and coolant passages in the engine. Distilled water does not have these issues, but also does not have any additives to prevent breakdown of the cooling system.
Open or closed system it wouldn't really matter, it's more a function of time. The longer you have those impurities in the system the greater the damage will be. Fresh is a mute point, because the fresh water is as dirty as the water you put in there the first time.
When I flushed mine I used antifreeze with a 1:1 ratio, that's what the owners manual said, drain the the tank on the side and the radiator, leave the radiator drain screw out and run fresh water through until it comes out clear. Let everything drain fully then put all the drains screws back in and fill the radiator up from the fill hole in the top, then fill the storage tank to the line and fire her up. Let it run for a few min and the check the fluid levels and add if nessesary before putting the plastics back over the radiator.
We always buy a 50-50 premixed antifreeze solution for any vehicles that we have here or for customer use, I have noticed a big difference in the cooling systems after using this antifreeze.............