The lawnmower, like any other machine, can malfunction when it gets hot. This can be frustrating, especially if you can only spare a few hours to work on your lawn. There are several reasons why your lawnmower may be overheating and failing when hot.
Your lawnmower may stop running when hot due to an overheated engine, air leaks, a clogged fuel system, or the carburetor not getting enough gas. It is also possible that the engine is not cooling as it runs because of a dirty air filter. Finally, worn-out pistons may also be the problem.
When troubleshooting the likely reason your lawnmower stopped running when hot, you should eliminate one possible cause before moving to another. Sometimes, you may have more than one fault to deal with, so it is best to check every possible cause to find a lasting solution. Keep reading to find out how to fix your mower.
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Clogged Air Filter
The air filter blocks dirt and dust from getting into the engine, and a gas lawn mower engine needs fuel, air, and a spark to run. As the air filter blocks impurities in the air from getting to the engine, the dust and other debris get stuck to the air filter.
A clogged air filter will not allow sufficient air to power the engine, and the result is less combustion, which naturally translates to less horsepower.
This video illustrates what you need to check when attempting to find reasons behind the problems with your lawn mower:
How To Fix
- If the filter is disposable, change it if it is dirty or clogged.
- If the foam air filter is brittle or has yellow or brown stains, it is worn out, so you should get a new one. However, if it is just dirty and clogged, you can wash it.
Dirty Fuel Filter
The fuel filter is designed to prevent the dirt in the fuel from getting to the carburetor. Unfortunately, the fuel filter gets clogged with dirt over time, especially if you do not regularly get rid of the dirty fuel.
A clogged fuel filter will release very little fuel, and the slow movement of fuel into the combustion chamber will cause the engine to stop running.
How you fix a clogged fuel filter depends on the type of filter, cleaning frequency, and when you last replaced the fuel filter. Follow these tips for your fuel filter:
- Metallic fuel filters are easy to clean.
- Replace nylon and paper filters. Should you wash them, they will lose shape, and this will make them ineffective.
Check the Spark Plugs
A faulty spark plug may be the reason your lawnmower stops running suddenly. The gap between the two electrodes has to be narrow for the spark to combust once it comes into contact with air and fuel.
A faulty spark plug may have a gap that is too wide to get the engine to run.
See Here’s How to Know if a Lawn Mower Spark Plug is Bad
- Replace faulty spark plugs.
The Champion RJ19LM Lawn Engine Spark Plug (link to Amazon) is compatible with multiple models of lawnmowers.
Small engines tend to release a lot of heat, and it needs an outlet. If the lawnmower has no means of releasing the heat, it will stop running. Unfortunately, unless you find the reason behind the engine overheating, the same will occur when you restart your lawnmower.
When the engine cools, you need to check for the possible reasons behind the heating engine:
- Check the fins for grass clippings and other debris that may have collected in the fins.
- Broken cooling fins can also cause the engine to overheat.
- The oil level is too low. The oil in the lawnmower engine, just like in other engines, works as a lubricant and a coolant. The engine will start heating when the oil level falls below the minimal limit.
How To Fix It
- Remove the lawnmower casing and fins, and then clean out all the debris. Use a brush to remove debris that is stuck on the surface.
- Replace broken cooling fins.
- Before starting the lawnmower, always check the oil level. If the lawnmower was already running before you realized the problem, let it cool and then add more oil.
The Briggs & Stratton 30W Engine Oil (link to Amazon) is a great detergent oil for lawnmowers.
Besides working as a coolant, oil is also a lubricant. It helps parts of the engine, such as the plugs and coils, to perform optimally. Without sufficient lubrication, the spark plugs will fail to run the engine.
Check the oil level before digging deeper for other causes of heating in the lawnmower.
- Add more oil.
- Change the oil once every summer or spring. Alternatively, you should change it after 50 hours of use. Dirty oil can do as much damage to the engine as low oil levels.
One way to tell if your lawnmower suffers from poor compression is by observing the starter rope. If it moves faster than before, you probably have compression problems.
Poor compression can lead to several problems.
For example, the pressure in the piston chamber will diminish, so the air and fuel being released will not be enough for the engine to run. The spark plugs will also fail to spark.
Worn-out pistons, broken piston seals, and bent pushrods are often to blame for the loss of compression. Check these to verify if loss of compression is to blame for your faulty lawnmower.
- Replace worn-out pistons.
- Tighten loose bolts on the cylinder head.
- Replace broken valve lifters or pushrods.
- If the fault is in the crankshaft, replace worn-out valves or damaged rings.
Faulty Fuel Lines
Collapsed, cracked, or clogged fuel lines affect the movement of fuel within the engine. This may cause the lawnmower to stop running suddenly. Fuel lines become faulty over time due to wear and tear.
However, sometimes, the gas you use may be responsible for the damage to the fuel lines.
Ethanol-based gas tends to form gum and varnish as it burns, which remain in the fuel lines. As they build up, the space within the lines becomes narrower, affecting the movement of gas. The engine will stop running because it is not receiving the fuel it needs to function optimally.
How To Fix It
- Add a fuel cleaner to the fuel and let it run. The cleaner will remove dirt and debris that has clogged the fuel lines. If the damage is extensive, you may be forced to replace the fuel lines.
When you notice your lawnmower heating when it is running, it signifies that something is wrong. Unfortunately, if this problem is not fixed, more parts may be damaged because they will overwork to keep the engine running. Troubleshooting possible causes will help isolate the problem and even solve it so that your lawnmower can keep running when in use.
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