Foaming compressor oil in older 375

by Nick
(California)

Ok, so my boss brought home this older 375 compressor. While I'm servicing it I change the compressor fluid filter and fill with just a 30wt motor oil. Which is what I put in our shop compressors. Start it, let it run for a while. I can't see any fluid in the sight glass so I shut it off, drain it of pressure, and open the compressor fill lid so I can add fluid to bring it to the proper level. Once opened foam slowly started to crawl up and out of the full tube.



3 questions

1. Should I have not opened the full lid after running it??
2. When do I check the fluid level? When running, or cold?
3.Is there any oil I can put in it that won't foam like that lol? I've read to use atf but idk jack about these large compressors


Pictures

http://s29.postimg.org/5ayed3o2f/image.jpg

http://s29.postimg.org/6c38fyufr/image.jpg

Comments for Foaming compressor oil in older 375

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Feb 06, 2015
foamy oil
by: Doug in s.d.ca

It's a Sullair 375 towable then? Any history? Did you run it for awhile before oil change?

Questions you ask:
1. Should I have not opened the full lid after running it??
Shouldn't matter

2. When do I check the fluid level? When running, or cold?
Yes - it doesn't matter enough to care (without foam, anyway)

3.Is there any oil I can put in it that won't foam like that lol? I've read to use atf but idk jack about these large compressors

So, you used ATF? Any idea what was in it before?
My guess is whatever was in it plus the atf made the foam. The picture looks like it's full, but if the foam is so bad you see only foam when it runs, you should probably drain it.
Ideally, you'd use sullair lubricant, but since it's out of warranty, you should be ok with non-detergent synthetic 30 weight. You might have to change it more than once to get rid of the foam.

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