Flushing cooling system

Cooling systems have a tendency for electrolysis. Before you flush next time take a DVOM set for MV and place one probe on the filler neck and the other suspended in the coolant. You will usually get some voltage if your system hasn't been flushed or cleaned in a while. A combination of corrosion over time and voltage being pulled through the block during start up etc... Acid is the real culprit so often a base like baking soda can be used when flushing to help neutralize the acidity. I do not recommend any type of corrosive "flush". Distilled water is a must when refilling.