When's the last time you changed your bike's antifreeze? Can't recall? Don't be embarrassed, neither can I, and that's probably true for far too many of us.
In techno-speak, antifreeze is a cyroprotectant, meaning that its substance is used to prevent the formation of ice crystals in something that would be better off unfrozen. In its primary role, antifreeze prevents the water in your bike's cooling system from turning into a rigid and highly destructive internal engine component whenever the temperature drops below freezing. Antifreeze also raises the boiling point of water (in this role it's referred to as a colligative agent) so it provides a degree of protection against overheating as well, Typically, antifreezes are created from a family of alcohols called glycols. Ethylene glycol is popular for use in things like internal combustion engines and solar heating systems, while its near-relative, propylene glycol, is sometimes used to prevent ice crystals from forming in ice cream. As you may imagine, confusing the two would have unpleasant repercussions, but at least the ice cream wouldn't overheat.
Because motorcycle engines use lots of easily corrosible materials, aluminum being one of the worst, antifreezes contain corrosion inhibitors-silicates, phosphates and borates being the most popular, to keep it alkaline. Unfortunately, the inhibitors don't last forever and as they're depleted, the antifreeze becomes acidic. Once that happens, internal corrosion starts to become an issue, which is why the OEMs recommend changing coolant regularly.
There is a caveat though. Many auto parts stores, particularly the ones that do a lot of heavy truck business, carry coolant test strips. In reality, these are nothing more than a piece of litmus paper that can be used to check the Ph of your coolant. If the coolant falls into the green zone, there's no need to replace it. If it doesn't, change is in the air.
Your shop or owner's manual should provide the 411, but essentially, it goes like this:
Locate the cooling system's drain bolt, which should be located at the system's lowest point.
Loosen the radiator cap, and remove the drain bolt. In many cases you'll also have to remove the reserve or expansion tank's siphon hose.
Drain the old antifreeze into a sealable container. Antifreeze is highly toxic, and it only takes a few ounces to kill a healthy adult. It has a very sweet taste, which makes it attractive to children and animals. I can't stress how dangerous this stuff is, so dispose of it quickly and properly, especially if you've got kids and pets, and promptly hose down any spills to dilute it.
If the system shows signs of corrosion, flush it using cool water. If it's really bad, you may need to remove the radiator and have it professionally cleaned.
Refill the system with fresh coolant. If you're using straight antifreeze, a 50-50 mix of antifreeze-to-water will protect your engine to -34°F and prevent boilover to 265°F. And yes, if possible, mix the stuff with distilled water. Personally, I find the pre-mixed stuff to be more convenient, but either type works fine. Oh yeah, if you're buying the antifreeze from a discount or auto supply shop, make sure it's approved for use in an aluminum block/head engine. These days it all should be, but who knows?
Once the fresh stuff is in, warm the engine up, and following the manual's instructions, bleed the air out of the system. Then top off the system.