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Old 04-24-2017, 06:15 AM   #2
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Join Date: Jan 2007
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Location: Grass Valley, CA
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Default Re: black foam in coolant after top end rebuild

Looks like someone put some "stopleak" type product in it before and now its coming back to bite you. My suggestion would be a coolant flush and possibly even removal of the lower block freeze plugs to check for gunk and remove as needed. Pretty common to see a bunch of gunk in the block, especially if the engine wasn't taken well care of. But the bubbles coming up to the top of the radiator while the engine is running is interesting. Have you preformed a cooling system pressure test after replacing the cylinder head gaskets?

Jeff Ismail
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