Determining the level electrolytic metal erosion with a voltmeter?

[Sean 96 McViper]

I read some ware that you can determine the level electrolytic metal erosion occurring in your cooling system using a voltmeter. By placing the positive probe into the coolant and the neg. probe on some metal part of the engine. A reading of 2 volts or higher is bad! Has anybody done this with their car, and is this a reasonable test?

I just bought a rad cap to fight this phenomenon as well, I thought it sounded like cheep insurance.