Years ago, a retired Mercedes mechanic told me that when anti-freeze is first taken from plants it is acidic. Chemicals are added to neutralize the acid, and as time goes by those chemicals loose their ability to neutralize the acid and the anti-freeze becomes acidic again. When the anti-freeze becomes acidic, at first it cleans the cooling system, then it eats away the metals and causes problems.
The retired Mercedes mechanic went on to say that if you open the radiator cap on an old cooling system that has never had the anti-freeze changed and everything looks clean, it my be that the anti-freeze has already turned to an acid and has cleaned the cooling system. And if you do not change it soon it will eat away the metals of the cooling system.
This is third hand information, or hear say, and I have no other information to back this up, but some labs that analyze fluids such as those that process oil samples, also will analyze coolant if you send them some. It may be that all you require is a simple PH test of the coolant. So if you want to maintain the coolant system perhaps you should be thinking about the age of the coolant and what you will replace it with.
BTW, other threads here on BITOG have brought up the topic of hydraulic fluids such as brake and PS. Apparently these systems have to use a fluid that absorbs moisture so that any moisture that manages to get into the system is absorbed by the fluid instead of not being absorbed and then existing in concentration is one or more sections of these systems and causing corrosion. However the amount of moisture that these fluids can absorb and prevent from causing damage is very small, such as it may be less than one percent of the volume of the fluid. Anywho, what this boils down to is that after years of use these fluids approach saturation of the amount of moisture they can handle, and should be replaced so these systems continue to be protected and run properly.
If you think about it, PS systems vent to atmosphere, and there fore every time the fluid heats up to normal operating temperature it expands, and when the system is shut off it cools and shrinks in volume. When it shrinks in volume ambient air that also contains moisture (water) is drawn into the air space above the fluid. Also PS fluid gets hot when it is used so it may be that even though PS fluid is exposed to small amounts of ambient air and the moisture that air contains, that when it is hot it boils off some of the moisture (water) that it has absorbed.
So along with anti-freeze, other fluids such a brake and PS should also be replace when they become too old, along with the original concern of maintaining the cooling system by replacing the old anti-freeze.
