I have read that measuring the voltage between the coolant and the engine block can show whether the coolant is corrosive. What voltage indicates the coolant is still safe to use? Just can't seem to effectively use the search engine.
I have not use the voltage test but found this,
"Take your DVOM, Place the Pos. lead in the coolant and the Neg. lead to ground from the battery. If you have a reading greater than .2V then your coolant is now a acid type battery. So the coolant needs to be changed. If less than .1 volts you are usually good for 6 months and need to check it again then."
I get good search results using Google with something like,
coolant corrosion test site: mtfca.com/discus/messages/
in the search box.
Here is some more links on the subject:
And, "The best way for testing is to use coolant test strips which measures the coolant’s pH, Reserve Alkalinity and Freeze Point / Boiling Point coolant to water mixture."
Recommended voltage reading are all over the place. I would recommend the test strips.
This is easier http://www.cooltrak.com/ Most independent shops can test it for you if you don't care to purchase the strips.