Grey sludge in brand new radiator - what does it mean.

Oklacarcollecto said
Maybe it is garbage still left from the old radiator that was still in the engine and possible crap they put in it to seal the leaks. As said before flush several times and then go from there.
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Not just an old fart but a smart fart. I hadn't thought of the left over sealin stuff. That's a great thought.