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Quick answers to common causes
There are a few common reasons why your lawnmower may be smoking white and spitting oil:
- Dirty air filter – A clogged air filter can restrict proper airflow to the engine causing it to run hot and smoke.
- Low oil level – If the oil level is low, the engine parts are not properly lubricated leading to overheating and smoking.
- Blown head gasket – A blown head gasket allows engine oil and coolant to mix, which can cause white smoke.
- Worn piston rings – Worn piston rings allow too much oil to get into the combustion chamber, leading to smoking.
Detailed explanations of potential causes
Here are more in-depth explanations of the most likely causes of a smoking, oil-spitting lawnmower engine:
Dirty Air Filter
The air filter on your lawnmower is responsible for keeping dust and debris out of the engine. Over time, the filter can become clogged with particulates, restricting airflow to the engine. Without proper airflow, the engine can overheat leading to smoking and oil spitting. Replacing a dirty air filter is an easy fix that can restore proper airflow and prevent overheating issues.
Low Oil Level
Oil serves the critical function of lubricating the moving parts inside your lawnmower’s engine. If the oil level falls too low, those internal components are not fully lubricated and will generate excess friction and heat when running. That heat can cause oil to burn and create white smoke coming from the engine. It can also thin out the oil, leading to less effective lubrication and oil spitting out of the engine onto the mower housing. Regularly checking the oil level and topping it off prevents low oil issues.
Blown Head Gasket
The head gasket seals the space between the engine block and cylinder head. Over time, this gasket can become damaged from overheating issues or normal wear and tear. A blown head gasket creates openings where engine oil and coolant can mix together. The result is often white smoke emanating from the engine due to burning oil and steam from leaking coolant. Replacing a damaged head gasket involves significant engine disassembly and should be left to a professional mechanic.
Worn Piston Rings
Inside the engine, piston rings seal the small gap between each piston and cylinder wall. Their job is to prevent excessive oil from getting into the combustion chamber. When the rings wear out, they lose compression and allow more oil to be burned in the engine, resulting in white smoke in the exhaust. The smoke may be worse when accelerating, as more fuel and air rush past the worn rings. Worn piston rings usually require a full engine rebuild or replacement to fix properly.
When to Seek Professional Help
While some smoking lawn mower causes like a dirty air filter are easy DIY repairs, others like a blown head gasket require advanced technical skills and tools. Here are some good guidelines on when to seek help from a professional:
- White smoke continues after changing the air filter and oil
- You find signs of oil and coolant mixing together
- The mower is burning excessive amounts of oil between changes
- You lack the technical confidence to disassemble major engine components
Reputable small engine repair shops have the expertise to properly diagnose and fix internal engine issues. They can also identify if repairable damage is beyond the value of your lawnmower and that a new unit may be the most cost-effective solution.
Interim Steps to Prevent Further Damage
While waiting for shop availability or parts shipments, you’ll want to take some simple steps to prevent additional damage:
- Stop using the lawnmower immediately to prevent overheating or seizing.
- Allow the engine to fully cool before transporting to avoid burns.
- Carefully clean accumulated debris, oil drips, and grass clippings.
- Disconnect the spark plug wire to prevent accidental starting.
- Store the mower in a clean, dry place away from rain and moisture.
Proper interim care protects your investment and prevents avoidable issues that compound the required repairs.
Preventative Maintenance for a Healthy Lawnmower
Smoking and oil spitting are often symptoms of an underlying lack of preventive maintenance. Here are some proactive care steps that can maximize your lawnmower’s life and performance:
Regular Oil Changes
Oil Type | Change Interval |
---|---|
Conventional oil | Every 25 hours of use |
Synthetic blend oil | Every 50 hours of use |
Full synthetic oil | Every 100 hours of use |
- Check oil level before each use and top off as needed.
- Replace oil filters at least once a season.
- Use the oil weight recommended by the mower manufacturer.
Air Filter Replacement
- Inspect air filters at least monthly and replace as needed.
- Clean foam filters can often be reused with new oil.
- Replace paper filters at least once a season.
- Use OEM spec replacement filters for proper fit and performance.
Cooling System Maintenance
- Remove debris clippings blocking air intake and cooling fins.
- Clean the underside and check engine mounting bolts.
- Tighten loose fan blades that can rob cooling power.
- Confirm the throttle linkage is closing fully when released.
Spark Plug Care
- Inspect spark plugs at 100-hour intervals.
- Look for cracked porcelain, electrode wear, or excessive deposits.
- Set the gap per manufacturer specifications.
- Replace with the specified OEM plug to avoid performance issues.
Conclusion
White smoke and oil spitting from your lawnmower is usually a sign of underlying engine issues that require prompt attention. Start with DIY fixes like replacing the air filter and topping off oil. But for persistent issues or serious engine damage, rely on a professional for proper diagnosis and repairs. With preventative maintenance and prompt response to problems, your lawnmower can have a long and healthy life ahead. Let us know if you have any other questions!