GM has been using Dex Cool since 1996. Their recommendation is 5 years or 150,000 miles, whichever comes first. It works really well. They also recommend distilled water. I am not sure about the voltmeter test. It has been a long time since I tried it. Dex Cool was formulated to better protect aluminum components better than the previous coolant. A lot of problems with it have been from the gaskets with the particular engines that it was put in. I have used it and will continue to use it in my Pontiac's.
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