You’ve been mowing along for a while when all of a sudden your lawn mower quits running. This is a common occurrence that many homeowners experience some time during the life of their lawn mower.
A John Deere lawn mower quits when hot due to a plugged air filter; old fuel; dirty carburetor; the wrong type of engine oil; too much or too little engine oil; clogged cooling fins; bad ignition coil; bad fuel cap, or plugged lawn mower deck.
Follow the safety precautions listed in the operator’s manual. Always remove the spark plug wire prior to performing any repairs. Wait for the engine to cool and for all moving parts to stop.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
10 Reasons a John Deere Lawn Mower Shuts Off When Hot
Plugged Air Filter
The first thing I check when the mower shuts down is the air filter. When mowing in dirty dusty conditions, the air filter can become plugged keeping a good flow of air from getting to the engine.
Without sufficient air, the engine isn’t able to form combustion and your John Deere mower will quit running.
It’s important to check the air filter before each use to ensure it is in good condition. I like to start out each season with a new air filter and then clean it several times throughout the season.
If you use your mower more than the average homeowner, you will need to clean and replace the filter more often.
SOLUTION: Here are instructions to clean a paper air filter and foam pre-filter (if your engine uses a foam pre-filter). For all other types of filters consult your operator’s manual.
Clean a Paper Air Filter
- Remove the air filter from the air filter housing.
- Wipe the remaining dirt from the housing. Don’t let any dirt or debris fall into the air intake.
- If your filter uses a foam pre-filter, remove the pre-filter.
- Tap the paper air filter against a solid surface to loosen the dirt and remove as much as possible.
- Hold your filter up to a light to check for light shining through the paper.
- Reuse the filter if you can see light shine through the paper element. Use a new air filter when you cannot see light, the filter is extremely dirty, covered in oil, or damaged.
Clean a John Deere Foam Pre-Cleaner: This is a foam filter used in combination with a primary paper filter. DO NOT add oil to a foam pre-cleaner. It can damage the paper filter.
- Inspect the filter to ensure it is in good condition. If it is brittle, torn, or has dark spots it’s time to purchase a new one.
- Wash the foam filter using mild detergent and water to remove the dirt and oil from your filter.
- Rinse until all the soap is removed and the water runs clear.
- Squeeze excess water and lay flat to air dry. Placing the filter in the sun will help speed up the drying process.
- Once dry, place the foam pre-cleaner onto the paper filter.
Bad or Old Fuel
Another thing that can cause your mower to quit running is old gas. Gas doesn’t just suddenly cause a John Deere to stop running.
Old gas breaks down and leaves behind varnish that builds up in the fuel system over time. The varnish and gummy deposits can cause fuel restrictions where one day your mower will quit after you’ve been running it for a while.
To minimize future fuel issues, use the right kind of gas and understand how to properly care for and store it. Read my article This is the Gas to Use in Your John Deere Lawn Mower to learn more.
SOLUTION: Drain old gas from the fuel tank using a siphon and dispose of it properly. Mix fresh gas with a fuel additive to stabilize and clean the fuel system. Once mixed, add it to the fuel tank.
I use a product called Sea Foam Motor Treatment in my fuel because it has cleaning agents for the engine and the fuel system. Read more about the advantages of using Sea Foam in your fuel system in my article here.
If you still have a clog in your fuel system after changing your fuel and using a fuel system cleaner, check out my article on why a mower isn’t getting gas for other items that can cause a lack of fuel.
Dirty Carburetor
The carburetor’s function is to mix fuel with air to create combustion in the engine so the mower starts and runs. The deposits left behind by old gas can plug the fuel jet and cause small internal parts to stick.
A carburetor failure can cause a mower to quit after it gets hot when sufficient fuel isn’t getting to the engine.
To narrow down the issue to the carburetor, first, confirm you are getting a good supply of fuel to the carburetor. If you aren’t, you need to look for a restriction in the fuel filter or fuel line, or for a fuel pump failure.
Second, remove the air filter and spray carburetor cleaner into the air intake. Start the mower and allow it to run. If it begins to run sluggish and then shuts down after the carburetor cleaner is burned, you may have a problem with the carburetor.
SOLUTION: If you are a little mechanical and don’t mind working with small parts, you should be able to disassemble and clean your John Deere carburetor following the instructions in this guide.
Unsure about tackling the cleaning of your carburetor? Have your local lawn mower repair shop clean it for you. Another option to fix your carburetor issues is purchasing and installing a new carburetor.
Wrong Engine Oil
It is best to use air-cooled engine oil that contains a high concentration of zinc. Zinc is an additive used as a cooling agent.
This type of oil varies from the oil used in cars. A car uses water in a liquid to cool the engine while a John Deere gas lawn mower uses air to cool its small engine.
Most lawn mower small engine manufacturers recommend using SAE30 or 10W-30 engine oil. You may need to change your oil viscosity to 20W-50 when operating in higher ambient temperatures.
Use this chart along with your owner’s manual as a reference to select the correct engine oil for your mower so it doesn’t result in overheating your engine.
SOLUTION: Drain the engine oil. Fill the crankcase with fresh oil using the viscosity recommended by the engine manufacturer that is sufficient for the ambient temperature.
Too Much Engine Oil
When there is too much engine oil in your mower, the engine may shut down. Too much oil causes the crankshaft and rod to have to push through excess oil so they are unable to rotate freely.
It can increase crankcase pressure and put internal parts under load causing the engine to quit when it gets hot.
Additionally, the engine may run terribly and shut down when too much oil creates smoke that clogs the air filter. When the filter is unable to get clean air, your mower may shut off while mowing.
SOLUTION: Remove excess oil so you have the correct amount of oil in your mower as specified by the engine manufacturer. Remove the spark plug wire and then drain a little oil using one of the following methods:
- Drain Plug: Quickly remove and replace your drain plug to only remove a little oil
- Oil Filter: Remove the oil filter. Have a rag ready to collect a little oil out of the filter.
- Oil Fill Hole: Some push mowers won’t have a drain plug or oil filter. You’ll have to tip over your mower to remove a little oil out of the oil fill hole. Keep the carburetor and air filter on the high side when tilting your mower.
- Oil Extractor Pump: Use an oil evacuator to vacuum a little oil out of the oil fill area.
- Turkey Baster: Use a turkey baster to suck a little oil out of the oil fill.
Check your engine oil level and add or drain more oil if needed. Once you have corrected the oil level, check and replace your air filter if it has signs of oil on it.
Too Little Engine Oil
With an oil level that is lower than the manufacturer’s recommended level, your mower may quit when it gets hot. Oil is required to lubricate the internal parts of the engine so they move smoothly.
Operating a mower with low engine oil causes the oil to heat up and thicken increasing friction in the engine.
SOLUTION: You can attempt changing your engine oil and bringing it to the correct level. However, most of the time, once your mower shuts down due to running on low oil, the simple fix of an oil change will not work.
Most likely, you have internal engine damage that requires a small engine mechanic to perform tests to properly identify your engine problem.
Regularly checking the engine oil level is a preventative measure you need to take prior to each mowing. Low engine oil can indicate the engine is burning or using oil. It may also indicate you have an engine oil leak. Read more about this in my article on overheating.
Damaged or Clogged Engine Cooling Fins
Cleaning your engine cooling fins needs to be completed annually and check periodically throughout the season. Debris and dirt can plug the fins and prevent them from dissipating heat from the engine block and cylinder to keep them cool.
Broken or clogged cooling fins or a buildup of debris around the engine can be the cause of your mower to shutting off.
SOLUTION: Remove debris around your cooling fins and replace any broken fins. Remove debris collecting under your engine shrouds and confirm the heat shield is securely in place.
Bad Ignition Coil
When the ignition coil gets hot it can stop working causing your mower to shut down. The windings on the coil separate and short out. A faulty ignition coil won’t be able to provide sufficient voltage to the spark plug.
SOLUTION: First, confirm you are running a good spark plug. Next, use an ohmmeter to test your ignition coil to confirm there is no break in the continuity of the coil. Replace when you find a faulty coil.
Bad Fuel Cap
A gas cap has a built-in vent that allows air to pass through the cap. This is necessary to equalize the air pressure inside the tank with the air pressure outside of it.
When fuel is being consumed, air needs to be able to flow into the tank. This isn’t possible if the gas cap has a plugged vent.
A plugged fuel tank vent will restrict fuel flow because the tank will form a vacuum because air is no longer able to get into the tank. This will cause a John Deere to shut off after it’s been running for a while.
SOLUTION: Replace your gas cap if the mower runs while the fuel cap is loosened to allow air into the tank and quits after a short running time with the cap installed.
Clogged Mower Deck & Dull Blades
Not only will a clogged mower deck and dull blades leave you with a bad cut, but it can also cause the mower to bog down and quit because the engine is under load.
The engine must work harder to move the mower blades through a bunch of debris with each turn. This causes extra strain on the engine that can cause it to bog down and quit.
In addition to a clogged mower deck, dull mower blades will further magnify the problem causing your engine to overload and shut down.
SOLUTION: Sharpen your mower blades and scrape your deck to keep your mower’s cut at its best and prevent the mower from being overworked.
Avoid mowing the lawn in wet conditions. Wet grass is more prone to collecting under the deck and clumping in your yard.