Diagnosis
The most common cause is a failure of the bar oil reservoir's venting system. The small vent hole in the oil cap can become clogged with sawdust or congealed oil. As temperature changes (like a warm garage cooling at night), air inside the tank contracts, drawing in air. If the vent is blocked, this creates a vacuum that can later equalize by slowly pushing oil past the main cap seal or O-ring. A damaged, missing, or pinched O-ring on the cap is the other primary culprit, providing a direct path for leakage.
How to Fix It
- Remove the bar oil cap and thoroughly clean the entire cap, paying special attention to the tiny vent hole in its center. Use a needle, pin, or compressed air to clear it.
- Inspect the black rubber O-ring on the cap for any cracks, nicks, or flat spots. Clean it and the mating surface on the tank.
- Reinstall the cap, ensuring the O-ring is seated properly and the cap is tightened firmly by hand—do not overtighten.
- Wipe the saw completely clean, then store it lying on its side (as if making a cut) on a piece of cardboard. Check after several hours to confirm the leak has stopped.
If That Didn't Work
Inspect the plastic oil reservoir itself, especially around the fill neck and seams, for hairline cracks. Ensure the oil tank is not overfilled; the correct level is just below the fill neck. If the cap and O-ring are not the issue, the internal oil pump seals might be faulty, allowing oil to seep back into the tank and overflow. For cracks or suspected pump issues, contact Greenworks support for a replacement part.
Heads Up
Always use proper bar and chain oil, which is tackier than motor oil and designed not to leak as easily. Never store the chainsaw upright or with the bar pointed downward, as this positions the oil cap at the lowest point, encouraging seepage. The side-storage position is recommended.