# Air compressor oil continues to be black



## RedCurl

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!:tango_face_sad:
What am I doing wrong?


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## Romore

I would suspect the pump was badly overheated, the oil is burnt .


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## adam

Air compressor is old and may be its want a service. Only oil change does not solve your problem.


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## joyjafor

the compressor has been old enough and the piston and cylinder may have rusted. Change both of them. It may solve your problem.


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## motormonkey

After fifty years, a lot of gunk and crud can settle out of the oil, and this stuff can set up like concrete in the sump of the compressor. It could be that fifty years worth of gunk and crud are still in the bottom of the compressor, and your attempts at cleaning it out have only been partially successful. A little blackened oil from this is not necessarily a bad thing if that's the case. 

How does the compressor work? Does it build up adequate pressure? Does it overheat? Does it have excessive drag? Any abnormal noises? If it's working okay, put fresh oil in it and run it. If it's not working okay, it's probably time to disassemble it and figure out why.


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