Don Hall
Full Access Members
If you have a DMM, set it to volts, place the red lead on the battery positive - negative lead in the coolant with the engine running. If you have anywhere near .5 volts or more you might want to replace the heater core and radiator in the near future before they give up the ghost on you.
An explanation of what stamp11127 is suggesting: http://sancarlosradiator.com/VoltageDrop/testing_for_electrolysis.htm