Letting it cycle from cold to warm, etc., will draw moisture into the sump.  Also, it may not be getting warm enough to help evaporate any moisture in the system.  You could try a space heater pointed at the sump area and run that continuously to keep the oil warm and limit the amount of cold moist air that it sucks back in as it cools.  You could also look into an engine block heater if the compressor has a dipstick.  I think using heat tape that you would use on gutters, for example, might be a fairly easy fix.  Try to keep the sump/case at 70 degrees F or higher.  Not sure how far away your compressor is from your garage but it you can draw warm air into the compressor intake you may also get less moisture into the pistons which could pass into the sump.

In reciprocating aircraft engines it needs to run the oil temp above 180ºf to "burn" off the condensation in the oil and crankcase.

When I built my garage years ago I mounted the furnace on the outside back wall with the ducts through the wall. That puts the fire outside my very fume filled building. The furnace is big enough to maintain good temp inside for painting. My problem is that I built a lean-to big enough to house my compressor as well. This compressor is 30 years old and still pumps up from empty in same amount of time it took when new, so I don't think it is completely shot. Just recently it started to freeze up like this which is due to the weather pattern we are having right now with high humidity and fluctuating temps that freeze at night. I don't heat the garage round the clock unless I am painting. I thought about a calrod heating element in the drain plug hole, but the splasher hits it.
I may try the no freeze tapes around the crank case to keep it warm enough to minimize condensation.
But, I still need to get the excess of moisture out that is in there right now. I need to find some kind of flush or oil that can absorb the moisture and get it out.

Are you running non-detergent air compressor oil or an automotive oil?  Most air compressor specific oils are designed to minimize the mixing of water and oil.  One site suggested running the compressor continuously using a buffer or some other tool to get it good and hot and then continue to run.  Proper oil (not assuming you are not using the proper oil now) and minimizing hot to cold cycles (keeping the sump heated) should straighten it out.  

Here are some suggestions  https://www.machinerylubrication.com/Read/864/flush-gearbox 

Another method that may help in your case is to use a low pressure desiccant dried air source which blows continuously through the sump.  We're talking 1 psi or less.  Basically, by creating a slight positive pressure in the sump when running or not running, cold air from the outside will not enter the sump as it cools down.  So, a small dryer and very low pressure regulator are all that may be needed.  Also, you can buy desiccant breathers to use on the sump.  Rather than venting to air, install a desiccant breather.  When the compressor cools, it will pull dried air into the sump.

Some sites recommend a double flush to get the current water out.  Drain completely, refill, drain, and fill again.  If there is residual goo below the drain plug, you could try to suck some of that out with a small tube with vacuum or a syringe.
 

Is there room to install an electric heat element under base of compressor to keep oil warm?
I would also install a thermostat control so it doesn’t run all of time, just when cold.

Heat tape for roof or pipes may be a good idea for tank so condensation doesn’t freeze and plug drain on tank. I would place insulation around tank over the pipe wrap. Just like a hot water tank.  I like the idea of the automatic system too as well as the desiccant for air intake.

You could make a simple intake with some pvc pipe that directs intake air through desiccant.
Just make sure it large enough and it doesn’t inhale desiccant into compressor.
If it could draw warm air from shop would help as mentioned already.

Could also use some rigid insulation (reflective too) and surround the compressor as well.
Then there’s the reflective bubble wrap.

Last edited by Nos681 (2/01/2020 9:06 AM)

Have you thought  about running a heat duct from your furnace to your air compressor lean-to? That should give you enough heat to keep your compressor from freezing up in the winter and in the summer you can close the duct  to the lean-to. Be sure to insulate the duct work if you run it on the outside. Side note if your lean-to is not inclosed you may want to wall it up  if you run a heat duct to the lean-to.

Last edited by flamingpony (2/09/2020 10:22 AM)