(I found this in the MT article Ari referenced - anybody BTDT? I'm gonna try
it tomorrow...)

Because of the stored electricity inside the system, the

                               coolant can also be tested with an ordinary
digital

                               voltmeter as described in the book "Automotive

                               Engines: Theory & Servicing," by Herbert
Ellinger and

                               James Halderman (Prentice Hall). With the
instrument

                               on its lowest voltage setting, insert one
lead into the

                               coolant and attach the other lead to a good
engine

                               ground or to the negative battery terminal.
A reading of

                               less than 0.2 volts is acceptable; 0.5V is
borderline;

                               0.7V or higher is unacceptable

Austin