I bought a 2003 cargo van used and have been following the Dex-Cool issues since looking into changing all the fluids.

The topic of pH testing the radiator fluid to determine if it is still potent AND protecting the metal against corrosion seems to be the most direct way to check if changing the coolant is in order. Although if the coolant is cloudy or thick or different colors of coolant are known to have been mixed it is reported that changing the coolant is the best policy.

I'm not finding specific numbers in all the discussions that are specific to brands of anti-freeze or in the bottle and mixed valves.

So here is a place to start. Add your numbers if you have them.
Note my first error in this exercise was in how to use the pH test strip. In using Hydrion (insta-chek 0-13) test strip off a roll - the test strip is to be dipped and immediately compared to the color chart. Waiting 5 seconds makes a difference depending on what is being tested. I do not know if this is the universal method so check with the manufacturer of what you are using.

I purchased Prestone GM Dex-Cool.
Out of the bottle the pH test = 8+.
Mixed 50/50 with distilled water the pH test = 7.
For the coolant in the van at 54125 miles the pH test = 7.

2003
Chevy Express 3500

 

old dexcool turns into an acid factory that eats gaskets. If your at pH 7 your ok as that is neutral.
There are other factors to consider; like corrosion inhibitors that wear out. So if in doubt...change it out.

 

Other than the observations I mentioned how would you test for active or depleted corrosion inhibitors?

To my understanding it is the pH test that determines the quality of the corrosion inhibitors.