The separator tank is overfilled. Excess oil floods the separator element, and oil gets pushed into the compressed air lines.

What you'll see

Oil carry-over that starts immediately after an oil top-up or oil change. The compressor was fine before, and now there's oil in the air. The oil sight glass shows the level above the maximum mark.
Before you assume this is the problem

If the oil level is at the correct mark and you still have oil carry-over, the problem is elsewhere. Check the separator element, scavenge line, and MPV. See: Separator Element Worn, Scavenge Line Blocked.

Could also be:

See all causes of oil carry-over →

How to diagnose

  1. Check the oil level sight glass

    Look at the oil level indicator on the separator vessel while the compressor is running unloaded. The level should be in the upper part of the green zone -- not above it. Important: check the level during unloaded running, not when stopped. When the machine stops, oil drains back from the cooler and piping into the vessel, so the level appears higher than during operation.
    Result: Oil above maximum mark during unload running = overfilled.

How to fix it

  1. Drain excess oil

    Drain oil until the level is at the correct mark. Fill to the level mark, not higher. On most machines this means filling to the middle or upper portion of the sight glass during unloaded running. Check the service manual for your specific machine.

Common mistakes

The most common mistake is checking oil level with the compressor stopped and filling to the top. When the machine starts, oil from the vessel gets pumped into the cooler and piping -- the level drops. People see this drop, panic, and add more oil. Then when the machine stops, all that oil drains back and now the vessel is overfilled. Always check and fill during unloaded running.

Parts & tools

Drain container. No special parts needed -- just remove excess oil.

Review safety precautions before starting →