Air compressor oil continues to be black
I got this air compressor from my dad that passed away.
I removed the opil and as expected it was black.
So I removed the front plate (it is a single piston reciprocating compressor, probably 50 years old) and cleaned the well. I then inserted more clean transparent oil and ran the compressor for a few minutes and changed the oil. It was black. I did this 3 times and it was always black with black sediments and reducing amounts of very fine metal particles.
So I filled the compressor well with diesel fuel to rinse it...and it was black
Then I inserted turpentine (10 times) to wash it and all turp fills came out black!
What am I doing wrong?