Air compressor oil change

[williammcneely]

How often do you change your air compressor oil? I changed mine a little over a year ago. The oil had turned a milky color from condensation. I recently noticed it was turning white again so I did a second change. I noticed when draining the oil that there was black chunks coming out.

I removed the sight glass from the side of the compressor to take a look inside. The bottom of the base was covered with 1/4" of sludge. I think this may of been mold. This compressor sits more than it is used, but when I use it it is for several hours at a time.

ANyone else ever have this type of sludge? Sorry no pics.

 

[malibulvr]

This reminds me that I have never changed mine and I think I bought it back in 94...

 

[softailgarage]

I recently tore down my dads old 10 gallon sears model he bought back in the early 70's. The drain plug was frozen solid and it had never been drained, I had to drill it out. I got about a quart of milky fluid with chunks also. Now, I have a 60 gallon upright. I use Mobil 1 synthetic and change the oil about every 3 months. I drain the tank every other day, unless it being used heavily (sand blasting for extended periods of time), then I drain it at least once a day, sometimes more depending on the temperature.

 

[Diverbill45]

I change my oil every 400 hours or every 3 months, whichever comes first.

No matter how long I run my compressor, at the end of ech day it is shut off and the tank is drained of all condensation. I always leave some pressure in the tank in order to help keep rust from building up inside. Sooner or later rust will start to form inside the tank, over a long period of time, but if you leave some pressure in the tank it will take longer for the rust to start forming.

Hope this helps.

 

[chris142]

We change ours 2x a yr.

 

[aka Larry]

Mine is only used a few hours on the weekends at most, but I still change it once a year.

 

[mayday0017]

What does rust have to do with pressure? Not a smart *** comment an honest question....

 

[thom1968]

What does rust have to do with pressure? Not a smart *** comment an honest question....

Ditto. Seems to me since rust is oxidation, the more pressure, the more oxygen available, the faster the rust builds up....

 

[gungatim]

I change mine every year or so. Never seen any chunks or milky oil come out, usually pretty clean. I use non-detergent oil, is that the consensus or do most folks use regular automotive motor oil?

 

[b-body-bob]

^ I've read that any device that doesn't have an oil filter should use non-detergent oil, because detergent oil holds contaminants in suspension, but non-detergent lets the garbage drop out.

 

[zkling]

I change mine once per year. But it is run <4 hrs per week on average and kept in the garage where it doesn't get cold or super hot. 30wt ND oil, is cheap insurance in my mind.

 

[Diverbill45]

The question was asked about rust and pressure and all I can say is that I've been a certified scuba diver since I was 15 (1960) and I've been told quite a few times, from different dive shop operators, that you should always leave some pressure in your dive tanks. I've asked why and was always told the same thing, .... it helps the slow down the process of corrossion (alumnium tanks) and rust (steel tanks) inside the tanks. When air is being compressed it will generate heat. After the filling process is stopped, the compressed air will cool down causing some moisture to form. So without a way to dry the air being compressed, there is always going to be some moisture present .

All scuba tanks have to be visually tested every year and hydro tested every 5 years. I have a couple of tanks that date back to the late 70's and they still pass the visual and hydro tests.

Now I know there's a BIG difference in the pressures contained in a compressor tank and a scuba tank (175 lbs. for compressors, with some industrial compressors going as high as 250lbs. vs. 3200 lbs for scuba tanks). Also there's a difference in the type of filtering of the air that is placed in scuba tanks, but the principal operation of filling both are the same, with the main exception that a scube tank is placed in a tub of cold water while filling, due to the amount of heat generated trying to compress that amount of air into a much smaller container.

Now, never researching this, from an engineering point of view but, just from working with pressure piping and pressure vessels for over the past 35 years, the amount of corrossion or rust from a system that is always pressurized and a system that is not, is different.

Not saying I'm right or wrong, it's just an observation. This is why I stated that I always try to leave my compressor tank with some pressure in it.

Maybe there's someone on this site that can clear this up.

 

[mayday0017]

Awesome response! I don't know if you are right or wrong either, no background but you have history in doing it not only yourself but many others out there so there must be some reason....

 

[mayday0017]

Hm... from what I am reading about scuba tanks is the air put into them already has the moisture removed so there is none to cause corrosion. The reason you want to store with a positive pressure is to keep moist are from ever entering the bottle like it would if you let it drop and equalize with the atmosphere. So the pressure itself for dive tanks has nothing to do with keeping corrosion from forming other then it doesn't allow any to enter the tank.

If that is the only reason (and researching) that is all I can find, this wouldn't apply to air compressors because they will always have humidity.

Anyone else want to chime in? For some reason I am very curious about his and want to know more

 

[b-body-bob]

I'd say the best way to avoid rust would be to leave the tank depressurized
.
.
.
with the drain open

 

[williammcneely]

The tank is not my concern, for I have a automatic drain with an extention pipe that keeps the water in the pipe and out of the tank. Just wondering if anyone has seen the same "mold" looking stuff that I see in my oil?

 

[skruft]

I change the oil every few years and drain any water from the tank about every month. I never got around to installing an automatic drain. All that comes out is a very little water with a whitish color and a smell of oil. The compressor is not in heavy use but has been running since 1977.