Hi All - just installed a pressure regulator (boost) on my 350/berkeley pump boat.  all that equipment checks out fine. the cooling system is closed - jet pump to exchanger to barr log exhaust.  the regulator knocks back the pressure and volume of water going thru the exchanger and out the logs.  after installation i noticed carbon in my antifreeze...with a closed system I am scratching my head trying to figure out how carbon could even get into the antifreeze.  anyone run across this before...thxs kenai