With the advent of extended life coolants, common cooling system maintenance has become sort of a lost art. Anti-freeze and related components now have a longer expected service life and these systems probably don't get the regular check-ups they deserve.

 

Most overlooked...

Cooling systems must have the correct ratio of anti-freeze and water. A 50/50 mix of anti-freeze and water is recommended for most situations. In extreme cold climates, a 60% concentration of anti-freeze can be used to increase freeze protection.

 

More is not always better...

Using too much anti-freeze affects coolant flow and heat transfer.  Something else to consider... Too much antifreeze can cost you each time you drive by reducing fuel mileage and horsepower. 

 

Consider your water quality.  Some people shop for the best quality anti-freeze but don't think quality of water that's mixed in the cooling system.  If your area has hard water, you may be adding high levels of calcium, magnesium, and other minerals to your cooling system.  This "hard water" circulates around the system and turns to scale.  Many parts stores carry purified cooling system water and most stores carry antifreeze that is pre-mixed with high quality water.

Invest in a good anti-freeze tester.    Don't be fooled by an ordinary hydrometer.  Use a refractometer for accurate results. 

Always allow the cooling system to fully cool before performing any cooling system service.

 http://www.eetcorp.com/antifreeze/antifreeze-faq.htm 

http://www.imcool.com/articles/antifreeze-coolant/whygoodradsgobad.php