The Dodge Challenger Message Board

Dave, I have about 800 miles on my 70 Rt and just about everything on this motor was taken apart and rebuilt. The radiator was boiled out and no leaks are present. I did notice a buildup on the neck of the radiator recently of a brown sludge like material. The water looks a bit rusty. The motor did sit for about 6 months prior to installation, as well as the radiator. Could the buildup be from this? I am concerned something else is entering the coolant. Other than bubbles, is their anyway to know if gases or oil are causing this? Any experience anyone?

Did you change the freeze plugs???? and are you running with coolent or just plain water??

Oil in the water looks like a light brown/cream sludge. I don't think gases would cause it. You say the radiator was 'boiled out' but was the engine 'hot tanked' or the water jacket flushed out?

I would flush the water jacket out again with a coolant flush solution added to the water (did it sit for a long time with just water in the block?) and then re-fill with the correct amount of anti-freeze and water. Then keep an eye on it and see what happens. It might be that there was some greasy sludge sitting in the bottom of the water jacket that has been stirred up with the re-build but if it was hot tanked that should not happen.