Rust brown inside compressor pump, not tank

[Squankum]

Drained the oil on my Kobalt 30g 1.8 hp 2 cylinder (cast iron inline 2 cylinder single stage) compressor the other night. When I peer into the drain hole, I see rust brown up to a "waterline" of where the oil used to be.

Is this normal? Because of cast iron, air, moisture, this isn't an internal combustion engine?

Is this because, hey, cheap Chinese stuff, there's no coating or paint on the inside?

Or?

Sticker on compressor says to use automotive full-detergent synthetic 10W-30.

 

[Outlawmws]

It almost sounds like it's water contaminated? Was it like a milk shake?

 

[Squankum]

The good news is, the oil wasn't milkshakey, no froth, no foam. Just rusty brown like the stain I saw inside, but still looked like oil.

Bought the compressor used off Craigslist but it looked mighty clean and lightly, if at all, used. It was two or three years old at the time, I'm guessing.

I've used it a bit but not oodles, in the past year I've had it.

Other issues:

I installed a 90 degree bend/pipe/ball valve drain on the bottom of it and always blow out the water at the end of a day where I've used it. I've always gotten nothing but water mist.

Lately, I've occasionally gotten dark gray/black oil in the mix. Looking back, I think it happened on days when I was using my grinders and it ran a lot. Also, there's a small oil leak somewhere on outside the motor that I er, haven't looked into, but hasn't been happening lately, just as I've not had oil out the bottom in the past two weeks. The fan seems to blow the leak from the front of the motor.

Recommended tools are listed on a sticker/chart on the tank of this compressor, and air sanders and grinders and other high volume things aren't recommended -- but I bet lots of folks are getting away with it. And I wasn't doing that much grinding. What happens if you make a compressor motor work too hard? (It's not like I went hard for an hour on it. Maybe 10, 15 minutes, and still, some pauses in the work, I'm sure it caught up and didn't run constantly.)

I just figured, not having changed the oil since I've bought it, I could start off with clean oil and see if that helps. But yeah, removing the fan belt sheet metal cage and inspecting the entire motor and the crank seal are high up the to-do list.

 

[mrpizza]

Most of the smaller compressors, and even a lot of the 60 gallon ones aren't rated for much over a 50% duty cycle rating. My Husky is a 50% rating, but I routinely blow past that. I just change the oil a little more frequently if I have beat down on it a lot. It sounds like some condensation built up in the crankcase and rusted the walls a little bit.

 

[mayday0017]

It's paint inside the unit, the "oil line" has stained or built up in an area so that area doesn't look the same color but if you take it apart it will be "rust brown" primer/paint too.... Unless your oil is milky white don't stress it, there is no way you could have rust inside there with all the oil splashing around.

 

[Squankum]

Unless your oil is milky white don't stress it, there is no way you could have rust inside there with all the oil splashing around.

Thanks! I'm not new to mechanical stuff, but I am to compressed air. Thanks for the reassurances, guys.

 

[Squankum]

DUMBO UPDATE

Last night, I installed a drain valve where the drain plug usually goes. As I fiddled about, cleaning the female threads in the block, I noticed that the paint had chipped around the drain plug hole in the past few days and... yep, that brick red/rust brown color is a base layer/primer paint. Mayday, you called it.

D'oh! Now I know.

Thanks again.