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This is Why Your John Deere Lawn Mower is Smoking

Smoke rolling out of your John Deere lawn mower can be alarming. You may immediately be thinking about the worst things that can cause smoke including an engine replacement. The thought of such a significant repair or possible lawn mower replacement can be very overwhelming. Sometimes signs of smoke isn’t as bad as you think and can be solved inexpensively if the problem is caught soon enough.

A John Deere lawn mower can begin smoking when oil burns due to an insufficient engine oil level, failed engine gasket, piston ring problem or valve train issue. An air restriction causing the engine to run rich can also contribute to smoking in your John Deere.

Let me share with you the different reasons your John Deere may be smoking. I’ll share some simple things to check and let you know when you need to consult a professional engine mechanic.

John Deere mower is smoking

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing or operating. Consult a professional if you don’t have the skills, knowledge or are not in the condition to perform the repair safely.

Reasons Why Your John Deere Lawn Mower Smokes

John Deere Lawn Mower Air Filter is Plugged

Your air filter’s main function is to keep dirt and debris from entering the air intake and damaging your engine. Your engine requires clean air to operate efficiently. It’s important to never run your John Deere mower without a filter. Dirt in the engine will compromise the life of your engine.

A plugged air filter restricts the amount of air being mixed with fuel causing the engine to run rich. This is when more fuel is being burned than air which can cause a black smoke to emit from your muffler.

When your air filter is plugged so air isn’t allowed to pass through the filter, your engine may pull air and oil out of the crankcase. A smoke will emit when the oil burns off.

Keeping your air filter clean is essential to keeping your John Deere running at its best. Replace your air filter annually and periodically check and clean it throughout the mowing season. You will need to check, clean and replace your air filter on a more frequent schedule when operating in dry dusty conditions.

Here are steps to clean your paper air filter:

  • Remove your John Deere air filter by removing your filter cover from the air filter housing and gently pull out the filter. Be careful so you don’t knock dirt into the air intake.
  • Wipe any dirt that remains in the housing with a clean dry rag.
  • Tap your air filter against a solid surface to knock as much loose dirt out of your air filter as possible. Never use an air compressor to blow out your paper filter.
  • Hold your filter up to the light. You can reuse your air filter if you can see light shine through the paper element. You need to replace your filter with a new one if you can’t see light.

Insufficient Engine Oil Level in Your John Deere Lawn Mower

Most engines installed in John Deere mowers have a dipstick to be used as a reference when filling your engine oil. You need to make sure the engine’s oil level registers on your dipstick to the full level between the dipstick marks. Having a crankcase with too little oil or too much oil can result in engine problems and smoking.

It is necessary to check your engine oil before each time you mow. Check your oil with your mower off and when your engine oil is cool. Failure to do so can result in avoidable engine damage.

John Deere Has a Low Engine Oil Level

A sufficient oil level is needed to lubricate the moving parts in your engine. When there isn’t enough oil in the crankcase, the lack of lubrication can cause increased friction. This friction causes a heat that can be so hot it melts parts and burns off oil creating a smoke.

You can try to change the engine oil and bring your oil to the correct level, but most of the time this won’t work. When your engine smokes and quits because of a lack of oil, an oil change usually won’t fix it. Most likely, the lack of lubrication has caused internal engine damage that needs to be diagnosed and repaired by a small engine mechanic.

John Deere Has a High Engine Oil Level

When your John Deere crankcase is overfilled with engine oil, increased pressure is built in the crankcase. This pressure pushes oil into your cylinder and up into the air intake through the valve train. This oil creates a smoke when it is burned off. Find out more about the effects of running your John Deere with too much oil here.

Correct the amount of engine oil by draining a little oil to bring the oil level between the marks on the dipstick. There are several ways you can drain some oil from your John Deere.

  • Drain plug / drain valve cap: Remove the plug or cap and replace quickly to only allow a little oil out of the crankcase.
  • Oil filter: Remove the air filter, and drain a little oil out of the filter. Reattach the filter.
  • Turkey baster: Use this household utensil to suction a little oil out of the engine fill hole. Do not reuse the baster for cooking purposes.
  • Oil evacuator: Vacuum a little oil from the oil fill area using an evacuator.

Once you have removed some oil, check your engine oil using the dipstick. Continue to add or remove oil until your oil is at the required level between the fill lines on the dipstick. Replace your air filter if you find oil has gotten on your filter.

Piston Ring Problem in Your John Deere Lawn Mower

After checking the engine oil and air filter, it gets a little harder diagnosing why your John Deere is smoking because the other causes are internal engine problems. There is a troubleshooting step that can be done that will indicate you have an internal problem.

The only issue is it won’t identify the exact cause of the internal problem. You will need to bring your John Deere to an experienced small engine mechanic to perform further diagnostics.

For this troubleshooting step, you are checking for signs of oil on your spark plug. Grab a 3/4” or 5/8” socket, depending on the engine used in your John Deere. Remove the spark plug(s) and check the tip for oil. Oil indicates there is something internally wrong with your engine.

Oil on the plug could indicate you have a piston ring or valve train problem. To diagnose either of these issues, the engine needs to be torn down and checked. An engine mechanic may find scoring in the cylinder wall. This scoring allows oil to enter the combustion chamber, burn off and create a smoke.

Valve Train Problem in Your John Deere Lawn Mower

A valve train problem can cause your John Deere mower to smoke. When the valve becomes overheated you can develop a burnt valve. While a red hot muffler can indicate you have a burnt valve or timing problem, the only way to confirm you have a burnt valve is by removing the cylinder head and performing a leak down test.

This test needs to be performed by a small engine mechanic. The mechanic will have to cut the valve and seat at certain angles if a burnt valve is found. The valve must be seated correctly to complete the engine combustion chamber.

Bad Engine Gasket in Your John Deere Lawn Mower

Oil can leak out of a bad engine gasket and onto your hot muffler causing your mower to smoke when the oil burns off. A bad gasket on your John Deere may not be that difficult to find and replace, but it can become increasingly harder to repair depending on its location.

Difference Between Blue and Black Smoke in Your John Deere Lawn Mower’s Engine

The color of smoke can give you a clue to what type of problem you are dealing with. Although, I highly recommend going through the steps above, the color of smoke can help confirm what you are finding or give you a place to start.

  • Black Smoke – This color usually is due to your John Deere’s engine running very rich. Running rich is when more fuel is being burned than air. Check your air filter for an air restriction. If this isn’t your problem, check for other air flow restrictions including a stuck choke.
  • Blue or White Smoke – This color smoke is due to burning excess oil. It is best to follow the steps above to identify the root cause starting with checking the engine oil level followed by checking for damage of the piston rings, valve train or engine gasket.

You invested a considerable amount of money in your John Deere lawn mower. Checking your engine oil level and air filter before each mowing could prevent costly repairs.