Symptoms
- Smoke has a distinct blue tint
- Noticeable oily smell in the exhaust
- May be worse right after starting
- Oil level might be over the full mark
Likely causes
- CommonOverfilled oilExtra oil gets drawn into the cylinder and burns, producing blue smoke.
- PossibleWorn piston ringsOn an aging engine, rings that no longer seal well let oil past into the combustion chamber.
- PossibleBad valve sealsLeaking valve seals allow oil to seep into the cylinder during operation.
- PossibleMower run while tipped or on a steep slopeRunning at extreme angles can let oil reach areas it shouldn't.
What to do
- Check the oil level and drain to the proper fill line if it's overfull.
- Run the mower on level ground only, and avoid steep slopes that can cause oil to migrate.
- Watch whether the smoke reduces to normal after correcting the oil level and running a few minutes.
- Check the oil for a burnt smell or unusual color which can indicate it's overdue for a change.
- If blue smoke persists at the correct oil level, the engine's rings or valve seals are likely worn.
- Consider the mower's age and value before investing in an engine rebuild versus replacement.
Tools and parts
- Dipstick/oil container
When to call a pro
Persistent blue smoke with correct oil level usually means internal engine wear; a mechanic can assess whether a rebuild is worth it versus replacing the mower.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.