Symptoms
- Oil puddle under the compressor
- Oily residue around the crankcase or pump base
- Low oil level on the sight glass
- Oil mist coming from the air outlet
Likely causes
- CommonLoose or worn oil drain plugThe plug at the bottom of the crankcase can loosen from vibration over time.
- CommonCrankcase overfilled with oilToo much oil gets churned up and pushed out through vents or seals.
- PossibleWorn crankcase gasket or sealGaskets harden and shrink with age and heat, allowing seepage.
- Less commonWorn piston rings pushing oil into the air streamThis shows up as oil mist in the compressed air rather than a puddle underneath.
What to do
- Unplug the compressor and wipe the crankcase area clean to see exactly where new oil appears from.
- Check the drain plug and any fill cap for tightness; snug them if loose, but don't overtighten.
- Check the oil level against the sight glass or dipstick mark; drain any excess if it's overfilled.
- Run the compressor briefly and watch the cleaned area for where oil reappears.
- If it's seeping from a gasket seam, plan to replace that gasket; this usually means removing the crankcase cover.
- If oil is showing up in the compressed air itself (oil mist at tools or in hoses), the piston rings are likely worn and need professional attention.
- Keep the area under the compressor clean going forward so new leaks are easy to spot early.
Tools and parts
- Rags
- Wrench for drain plug
- Replacement oil
Compressor crankcase gasketSearch: “air compressor pump crankcase gasket kit”
Compressor oilSearch: “air compressor pump oil”
When to call a pro
If oil is getting into the compressed air itself, have a technician inspect the piston rings and cylinder; this is a bigger job than a gasket swap.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.