Re: Radiator sludge
I'm guessing it simply has not had radiator inhibitor put in the cooling system as it is supposed to. Keep flushing the system until the water seems clear then perhaps run the vehicle with the heater turned to hot then reflush it again. You could even use some radiator flush product to try and clean it well.
Then refill system using the correct amount of inhibitor, usually glycol based, and run engine to operating temp with heater on and radiator cap off to bleed air from system. Check levels and put cap on. Make sure the overflow bottle is cleaned out too and the hose to the bottle is in good condition.
71 429SCJ Mustang