For any who may be interested, I have spent quite a bit of time web researching coolant related radiator problems. Based on the research I have done, the only value of measuring the voltage potential between coolant and ground, with the battery connected and electrical items switched both on and off, including the engine, and starter, is to determine if stray current due to poor grounds is contributing to radiator corrosion.
There are numerous commercial tests available to evaluate coolants, including evaluating a coolant's fitness for continued use.
Some firms have in the past advocated (and performed for a fee) conductance measurement of coolant in order to attempt to ascertain the total amount of dissolved solids in the coolant. These tests are not considered very useful, due to the fact that the vast majority of the conductance is due to the glycol in the coolant, and not the dissolved solids.
The suggestion raised in this thread that measuring coolant conductance may be useful is, on its face, a reasonable suggestion.
My comment that measuring the voltage to ground was not measuring conductance of the coolant was a polite way of saying "hey guys, you are on the wrong track in presuming that the voltage measurement is meaningful with respect to the coolant life remaining, particularly if you think your are measuring conductance of the coolant. The effects of the engine, radiator, and electrical system are what is primarily driving the voltage being measured and it is not reasonable to expect that these factors will remain constant enough over a period of time so that they can be ignored.
The statement that measuring voltage from coolant to ground while in the engine is the same as measuring the resistance or conductance of the coolant is just plan wrong, despite the many different ways Mike has tried to say he did or did not say that, and that regardless of whether he said this or that, that it is in fact true. It is not true, and proceeding as if it is would be a waste of anybody's time.
If anyone wants to further pursue using conductance to evaluate coolant life, then they need to accurately measure the conductance, and not what stray voltage happens to exist within the engine from time to time. A more rational starting point is to just find out what the industry is already doing in this field. I have already posted a website that provides a good jumping off point for anybody who is interested pursuing this further and that is
www.amalgatech.com. Look at the specific tests they offer, and review their tech documents. Despite the cheesy website, it appears they offer substantial expertise in this field. They directly comment on using conductance measurement to evaluate coolant life remaining.
With respect to voltage being measured with the battery disconnected, on the face of it, it is not surprising, as what you have is an aluminum radiator, which is extremely susceptible to galvanic action, coupled by coolant to a cast iron block capped by an aluminum head. For those inclined, measure the voltage from the aluminum core (outside the radiator) to the engine block and see what you get. I haven't done this, but I expect that the radiator and block are two plates in a oversize, inefficient, low capacity battery.
Doug does have it right that having a firm that understands engine coolant failure analysis examine the sludge would likely result in an expert opinion as to the immediate cause of the sludge, and addition, I expect, an enumeration of the most likely root causes.
Rich, you've elevated yourself to comical level. Electricity does follow the path of least resistance and this is a pillar of electrostatics. Ever heard of a short circuit? :-[ Take your own example. If you had a 12V battery across the two resistors you've named in parallel, guess how much of the current travels through the 100K ohm resistor. [waiting....]
