Originally posted by wildstoats
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This particle from Pelican might explain what happened.
Electrolysis
One failure mode associated with dirty coolant is known as electrolysis. Electrolysis occurs when stray electrical current routes itself through the engine coolant. The electricity is attempting to find the shortest path, and impurities in the coolant often generate a path of least resistance that the electricity travels across. The source of this stray electricity is often from electrical engine accessories which have not been properly grounded. A missing engine or transmission ground strap can also cause the coolant to become electrified. Sometimes the path of least resistance becomes a radiator, a heater hose, or even the heater core. These components are often well grounded, and offer a ground path from the engine to the chassis by means of the semi-conductive path of the coolant.
Electrolysis can destroy your engine quickly. Although it's semi-normal to have very small amounts of voltage potential in your coolant system, values greater than about a tenth of a volt can start reactions between the coolant and the metal in your engine. In particular, electrolysis affects primarily aluminum engine components, resulting in pitting and scaring of the aluminum surface. This eating away of the metal can cause coolant system leaks, and in particular, radiator leaks around aluminum welds. Cast-iron components are also vulnerable, but typically the aluminum metal parts fail first. On BMWs in particular, electrolysis can be easily seen attacking aluminum cylinder heads. Figure 1 shows a picture of the thermostat area of a cylinder head that has been partially damaged by electrolysis. Notice how the aluminum has been eaten away, and eroded by the chemical/electrical reactions.
The process works somewhat like electrical discharge machines (EDM). These machines work by passing a large electrical current through metal, literally zapping away bits of material until nothing remains. Unfortunately, the electrolysis process works in a similar way, zapping bits of metal in proportion to the amount of electrical current passing through the coolant. A poorly grounded starter can literally destroy a radiator or head within a matter of weeks, depending upon how often the car is started. A smaller current drain, like an electric cooling fan, may slowing erode components over many months.
How can you test for electrolysis? Other than actually seeing visible signs of erosion, you can perform a current flow test. Connect the negative terminal of a voltmeter to the chassis ground. Test for adequate continuity by touching another point on the chassis - the resistance should be near to zero. With the engine cold and running, submerge the positive probe into the coolant tank, making sure that the probe does not touch any metal parts. The voltage should be less than .10 volts. If not, methodically turn off or unplug each electrical accessory until the reading reads below .10 volts. Have an assistant switch accessories (like the A/C compressor, heater blower, etc.) while you measure the voltage.
If an accessory doesn't have an on/off switch, test it by temporarily running a ground from the housing of the accessory to the chassis. Ground each component and check the volt meter. If the wire restores a missing ground connection to the accessory, then you've found a component with a faulty ground.
During this test, be sure to check the starter. Not only will a poorly grounded starter struggle to turn over the engine, it will also zap away tremendous amounts of metal in your cooling system. Watch the meter carefully when starting the engine. Any voltage spike will indicate a faulty ground connection.
They are actually Bolle's with lenses that turn dark with sunlight and clear inside plus they have a prescription. I use them as my safety glasses. 
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