How to fix a lawnmower that’s been underwater, step by step


Lawnmowers are machines that are meant to be used outside in both cold and warm weather. The lawnmower versatility may cause various issues that can arise from either clogging of filters with dirt or may be caused by water exposure. Lawnmowers usually do not get upset when they get damp, but it is a different story if your lawnmower has been underwater. You are not the first one that drives a lawnmower in a pond, lakes, or other places with a lot of water. Or they get so much rain that it almost seems like they have been underwater. Depending upon the level of dampness, different scenarios may occur. All these various situations and their remedies will be discussed here.

How to fix a lawnmower that’s been underwater, step by step:

  • Step 1: Clean and dry the lawnmower
  • Step 2: Give the mower a diagnostic start
  • Step 3: Check the sparkplug
  • Step 4: Check the air filter, carburetor, and fuel quality
  • Step 5: Notice for any power drops or stoppages
  • Step 6: Check the cylinder head for cracks
  • Step 7: Clean all internal components if watermarks are present
  • Step 8: replace parts with permanent damage
  • Step 9: Reassemble and recheck
How to fix a lawnmower that's been underwater, step by step 1

This 9-step guide is a complete answer to most of the water problems. It is understandable if your lawnmower behaves badly after being wet. Before diving deeper into the different steps, we first need to understand the symptoms and risks involved.

Situations, Symptoms, and Severity

There can be mostly three different situations due to which this problem can occur.

Either the lawnmower was left uncovered, and a heavy rain damped the mower. Or, because the lawnmower was very dirty and you considered washing it, and now the mower is way too wet. Maybe you accidentally drove the mower into your pond or lake. Or another unforeseen problem resulted in your lawnmower being fully or partly underwater.

The problems that arise from these situations are pretty similar but differ in severity. It depends, of course, on how much from the lawnmower was underwater. The major symptoms of a lawnmower that has been underwater are as follows.

  • Difficulty in starting: You try to turn the mower on by turning the key or pulling the cord, but it will not respond.
  • Intermittent operation of the machine: The machine’s power just keeps dropping, and the operation is not as smooth as you will like it to be.
  • Sudden and unwanted power drops and stoppages: The mower first starts, but as soon as you ask some power from the engine, it dies.

These symptoms can be very misleading sometimes, so the history of the situations, as mentioned earlier, must be known.

Severity depends on the quantity of water and the place of action.

  • Splash of water on the air-filter: Due to this, water enters into the combustion chamber and will cause loss of power
  • Water droplets on the sparkplug head: This might lead to misfiring and excessive consumption of fuel along-with damage to the piston head
  • The battery was short-circuited: depending on how long the lawnmower has been underwater, but if the battery was submerged, it might have been quickly discharged. Being submerged can also cause the battery to fail.
  • The wetness of electric wires: Electricity and water are not a good combination and may cause a short circuit. This can lead to a fuse blow. Replace it with a new one. If your mower is more modern and has some electronics on board, this could fail as well.
  • Gas tank: If  the gas tank has been submerged, you should drain it and use fresh gas.
  • Direct contact of running engine with cold water: This is the fatal situation for the lawnmower. It may cause permanent damage to the cylinder block and leave the mower non-operational for good. Remedy will require a complete revamp to the block, and it will be very costly.

Whenever there is a chance that the water has harmed the mower, it is better to follow the machine’s steps in top-notch performing conditions. Whatsoever, might be the reason for the lawnmower getting wet, it might be or might not be dangerous. Any electrical connection getting wet will lead to a lot of trouble. The engine block exposed to water can cause permanent damage. There are situations where you should go directly for professional help. It is important to take proper care of the machine. In case you think the trouble might be huge, try waiting for the equipment to dry up completely on its own as well and then go for a complete check-up and treatment.

Equipment Required

To fix a lawnmower that has been underwater, you need the following tools:

  1. Torque wrench
  2. Screwdriver
  3. Old rag/ cleaning cloth
  4. Collection tank
  5. Grip pliers
  6. Blower/ heater
  7. Engine cleaner

Step by step guide to fix a lawnmower that has been underwater

•Step 1: Dry the lawnmower

If you get the lawnmower out of the water, the first task is to let as much water as possible drain away. Try to remove as much water as possible. If the lawnmower has been covered with dirty water, you can use a hose to clean the dirt.  

If most water has drained, use a clean piece of towel or cloth to absorb and clean away any water splashes on the lawnmower’s outer casing. Absorb water and squish it in an empty collector tray/ container. All apparent water and marks should be cleaned off. Using a blower, you can speed up the process. Open as places on the lawnmower as you you can open and try to remove as much water there as possible. Let the lawnmower further dry. When it is really dry, also in hard-to-reach places, you can continue with the next step.

•Step 2: Give the mower a diagnostic start

  • Start the lawnmower: Pull the starting chord of the mower and check whether it starts or not.
  • Observe for any symptoms: Closely listen for puffing sound or other signs of sparkplug damage.
  • Notice power demising: Notice the sound if the mower starts and then shuts-down instantly.

•Step 3: Check the sparkplug

Mostly moisture gathered on the tip of the sparkplug is the root of the problem.

  • Unscrew the plug: Using a torque wrench, unscrew the plug and check its electrodes.
  • Clean and check: Clean the plug, check the gap and the current insulation. Also, it is a better idea to clean any carbon deposits hindering the smooth operation.
  • Reinstall the plug: When the condition of the sparkplug seems well, reinstall it. If the sparkplug fails any test due to permanent damage, replace it with a new one.
  • Recheck: Recheck the operation of the mower.

•Step 4: Check the air filter, carburetor, and fuel quality

  • Uncover the body: Open the hood if your mower has one. Using a screwdriver and pliers, remove the plastic body cover of the mower
  • Locating the components: Identify the carburetor and air-filter location by following the fuel pipe and air intake duct (if any).
  • Remove the filter: Using grip pliers, remove the air filter cover and check the filter for clogging due to dirt or dampness due to water exposure.
  • Clean the filter: Clean the filter using a brush, wash it, and dry using the blower.
  • Check the carburetor: Check the carburetor gaskets and fuel intake pipe and observe for any moisture contents.
  • Check fuel quality: Drain the fuel in a collector tank and blow air in the fuel tank and pipe to remove moisture. Check the fuel quality. If it has a cloudy appearance, it means water was mixed with fuel. Pour in new gasoline. 
  • Reinstall all parts: after the check and cleaning process completes, reinstall all refurbished components. If some have permanent damage, replace it. 

•Step 5: Notice for any power drops or stoppages

If power drops, maybe something is wrong with the combustion compartment, and water has somehow entered the cylinder. It is also possible that the cylinder has cracked when the hot metal from the engine was quickly cooled with much colder water. The can lead to water or air entering the engine, cylinder, or crankcase.

Both of these are the most dangerous scenarios underwater and might result in permanent damage to the lawnmower.

•Step 6: Check the cylinder head for cracks

  • Make a visual observation first.
  • Air can be blown into the cylinder, and leaks can be checked by blocking the exhaust
  • A more complex method requires the use of an ultrasonic machine to check for cracks. This is probably more for a professional.

•Step 7: Clean all internal components if watermarks are present

  • Open the cylinder head by unscrewing the bolts present.
  • Check the blow marks and check the gasket condition. Replace the gasket if there is any damage.
  • Dry up the water using a clean cloth. And blow air to dry the chamber completely. 

•Step 8: replace parts with permanent damage

All parts from the carburetor, filter, gaskets, sparkplugs, or head gasket should be replaced if there is permanent damage. If there are any cracks in the cylinder block, proper repairing should be carried out using welding or any other means.

•Step 9: Reassemble and recheck

  • Reassemble the cylinder head, carburetor, fuel line, breather tube, air filter, and sparkplug. The cover should be placed back.
  • Pull the chord and give the mower a test start. Hopefully, the mower will start, and the various problems have been sorted out.

Precautionary Measures

  • Safety: Use proper safety gear, including gloves, coverall, and goggles
  • Ventilation: Perform all steps involving gasoline in the open air rather than the repair shop or garage’s closed and heat environment.
  • Use good quality parts: While replacing the parts, it is important to use the same parts as recommended by the manufacturer.
  • Water and electricity do not match: While operating high-voltage machines such as a blower or vacuum cleaner, insulation gloves and boots should be worn.
  • Be careful with air pressure: High pressure should never be used to blow in the ear, nose, eyes, or body part.

Related questions

1. How long to wait if the lawnmower engine gets flooded?

It is better to let the mower settle for 20 minutes. And also, open the mower’s fuel area so that the gasoline mixed with water gets evaporated on its own.

2. What is an easy way to check the presence of water in the lawnmower’s engine?

Check the engine dipstick. If there are water vapors or bubbles on the oil’s surface, it indicates water in the engine compartments.

3. Can WD-40 be used as a cleaner for a lawnmower carburetor or other parts?

Yes, WD-40 is an all-purpose cleaner and can be used for the carburetor, air filter, engine cleaning, and body cleaning.

Final Remarks

When you work with a lawnmower near a pond or lake, it is always possible that something goes wrong and the lawnmower is submerged. Or the lawnmower is exposed to some extreme rain. If your lawnmower is wet, you need to clean and dry it first. Then you have to check if it is still working fine. If that is not the case, you will have to complete a check-up, cleaning, repairing, and rechecking. In most cases, it is possible to have your machine working perfectly, and such that it can be used for many years to come.

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