[shorod]

Has a previous owner maybe put some stop leak in? Was the color dark, or was it more white? If more white, that may have been silicates that built up from not changing out the coolant regularly or from using tap water rather than de-ionized water. I'm making guesses here based off what I've heard others say, I'm no chemistry expert. Hopefully a similar build up is not in the heater cores.

-Rod