A mower that regularly overheats can be a real pain. Not only will your mower run rough, but it will also probably keep stalling. Now depending on the root cause of the overheating, your lawn mower might actually be suffering some damage. So, instead of struggling on, let’s see if we can figure out why your lawn mower is overheating.
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What Causes Lawn Mowers to Overheat?
A lawn mower can overheat for several different reasons, like the working environment, engine servicing, and general cleanliness. Here are eight common causes of lawn mower overheating:
- Lawn Mower Overworked
- Damaged or Dull Cutting Blades
- Clogged Cutting Deck
- Engine Running Lean
- Damaged Air Filter
- Lack of Engine Oil
- Cooling System Blocked
- Cooling System Defective
How to Tell if a Lawn Mower Is Overheating
A lot of the time, you might only realize that your lawn mower is overheating when it shuts off and stalls. But, sometimes, you might notice your lawn mower struggling as it’s getting ready to die. Depending on the issue, you might smell burning and hot metal as your mower gets hotter and hotter. So, if you notice anything unusual before your mower stalls, it’s best to stop the engine and allow your mower to cool down. Then you can work out what is going on.
How Do I Cool Down My Lawn Mower?
The easiest way to cool down an overheated lawn mower is to push the mower into the shade and wait. After twenty or thirty minutes, your lawn mower should be cool enough so that you can start to diagnose it. Alternatively, if you have a leaf blower handy, you can speed up the process by blowing cool air onto the engine. This will reduce the cooling process down to just a few minutes.
How Not to Cool a Lawn Mower Engine
I know that waiting for a mower to cool down can feel like an eternity, and you might be tempted to use a method faster than a leaf blower. But this is not a good idea. You may think pouring cold water from a garden hose onto the mower would do the trick and stop your mower from overheating. Well, it would, but it will also probably crack the engine at the same time. The sudden cold water on the engine’s hot metal would be too much of a shock and cause the expanded metal to contract too quickly. Even if your engine doesn’t crack, it will probably fracture and definitely weaken the metal. So, be patient and allow the engine to cool down gradually.
Why Does My Lawn Mower Stop Working When Hot?
The main thing that causes your lawn mower to stop working when hot is the over-expansion of the internal components of your mower engine. For example, as the temperature in the engine exceeds the working temperature, the metal components expand and cause friction. Not only does this friction causes additional heat, but it can grow so much that the engine doesn’t have enough room to move. So, if a piston expands bigger than the cylinder, the piston will seize, and the engine will stall. Depending on how much the various components expand and the damage caused, the mower may start again after it has cooled. But, if the engine seizes and locks up, then it’s likely the mower is too damaged to ever fire up again.
What Causes a Lawn Mower to Overheat (A Closer Look)
Now let’s take a closer look at what could cause your lawn mower to overheat. I’m pretty sure that if you are having an issue with your lawn mower overheating, then one of these potential causes will be the reason. Let’s dig in and find out.
Lawn Mower Overworked
One common cause for a lawn mower to overheat is if it is overworked. By this, I mean the mower is trying to mow more grass than it can cut. For example, if your lawn is very long, then your mower may not have enough power to cut it without overheating. The sheer volume of grass is probably too much for your mower to handle.
Damaged or Dull Cutting Blades
Mowing with damaged or dull blades is next on the list of what causes a lawn mower to overheat. If your mower is struggling to cut the grass with just one or two rotations of the blades, then your mower will have to stay in contact with the grass for longer. This is just the same as overworking your mower.
Clogged Cutting Deck
Having a clogged cutting deck is a knock-on effect of the blades not being able to discharge the grass quickly enough. If the blades can’t cut the grass fast enough, the grass will build up in the deck. Another way this can happen is if you are mowing wet grass. For example, mower blades can’t cut through wet grass easily, and wet grass clippings will quickly clump inside the deck and clog it. Again this puts the engine under strain and will cause the engine to overheat.
Engine Running Lean
If your mower engine runs lean, the ignited gasoline will generate additional heat in the cylinder head. This is because air-rich fuel (lean) burns hotter than fuel-rich fuel (rich). The cause of a lean mix is typically poor carburetor adjustment or an issue with the air intake. It is not likely that lean fuel will stop your engine and make it stall, but it will cause prolonged heat damage. Therefore you’ll want to take care of the issue as soon as possible.
Damaged Air Filter
A common air filter issue is that it gets clogged and makes the engine run rich. But if your air filter has a hole or is missing, your engine will run lean. Again, this has the same knock-on effect as having a poorly adjusted carburetor. So, once your mower has cooled down, pop out the air filter and make sure that it is not damaged.
Lack of Engine Oil
Every engine is designed to reach a certain temperature once it’s up and running. So regardless if you have a 2-cycle or a 4-cycle engine, you’ll need to use an appropriate oil to provide constant lubrication. Therefore, if your lawn mower is low on oil, has degraded oil, or doesn’t have enough oil in the 2-cycle mix, your mower will overheat. So, depending on your specific engine design, you’ll either want to check the mix ratio of oil to fuel or the oil in the sump.
Cooling System Blocked
Depending on how often and how thoroughly you clean your lawn mower, you may have a build-up of grass clippings and debris on the cooling fins if your lawn mower is air-cooled. These fins sit on top of the flywheel and create airflow over the engine. As a result, if the fins are clogged, your lawn mower will receive very little airflow and will likely start overheating in just a few minutes.
Cooling System Defective
It’s becoming more and more common for tractor-mowers and zero-turn mowers to use water cooling systems. These systems are similar to those found on cars, where water passes through the engine and then into a radiator to discharge heat. So, you want to ensure that both the cooling fluid is topped off and the radiator’s fins are not blocked. Again, if your mower’s cooling system is clogged, low on fluid, or broken, your lawn mower will overheat in just a few minutes.
How to Prevent a Lawn Mower Overheating (The Fixes)
So how do you prevent your lawn mower from overheating? Let’s find out.
Use Your Mower Within its Limits
One of the key factors when picking a lawn mower for your yard is knowing if the mower is up for the task. For example, if you have a large yard, then a little mower probably isn’t up for the task. So, if your mower struggles to get the job done, it may be time for a new lawn mower. One trick I have used before is renting a lawn mower from somewhere like Lowe’s or your local mower store. It’s an easy way to get a test mow with different types of mowers and find the right fit for your yard.
Always Use Good Blades
Lawn mower blades are a topic that I could talk about all day. There is so much information when it comes to blades, like the types of blades, the best angle to sharpen a lawn mower blade, how often to sharpen a blade, and even what to do with blades when you are finished with them. The main thing is that as long as you get these four points right, your mower won’t bog down and overheat.
Factors To Consider For Good Blades
- Have the right type of blade/s for the job.
- Make sure that the blade/s are not damaged.
- Make sure that the blade/s are correctly sharpened.
- Ensure that the blade/s are sharpened to the correct angle.
Keep the Cutting Deck Clear
Keeping your lawn mower’s cutting deck clear can be achieved in a few different ways. First, you can open the side/rear chute to discharge clippings straight out of the deck. The second way is to use a bagging system to collect the clipping from the deck for later disposal.
Now if you are using mulching blades and a mulching kit on your lawn mower, then you’ll actually want to keep the clipping in the deck as long as possible. This is so you can mulch the grass down into small bits. When mulching or doing regular mowing, it’s best to make sure that you are always mowing dry grass so that the grass doesn’t have the chance of sticking to the underside of the deck.
If you try all this and keep having issues with your deck clogging, I suggest you inspect your mower’s deck. For example, you could have an issue with a rusted mower deck, causing the grass clipping to cling on.
Pick the Right Cutting Height
There are several reasons why you might want to select a different cutting height when mowing your lawn. This could be the time of year, the type of grass, or as simple as wanting your lawn to be a specific height. So, what does this have to do with a lawn mower overheating? Well, the amount of grass your lawn mower has to cut at any one time will determine how hard your lawn mower has to work. So, if your lawn is pretty long, it would be a good idea to raise the deck and cut the lawn longer. If the grass is too long after mowing, you can lower the deck and mow over it again. This is called double cutting. It’s an easy trick to get around mowing long grass without putting too much strain on your mower’s engine and avoiding overheating.
Replace Damaged Air Filters
If your lawn mower is overheating due to a lean fuel mixture caused by a damaged air filter, then you’ll likely see a bit of white smoke blowing from your lawn mower’s exhaust pipe. This means you’ll want to install a replacement air filter as soon as possible. Here are the steps to install a new air filter on your lawn mower.
Steps to Install a Replacement Lawn Mower Air Filter
- Locate the air filter housing.
- Remove the air filter housing cover.
- Remove the old air filter.
- Wipe down the inside of the filter housing and cover.
- Install the new air filter into the air filter housing.
- Attach the air filter cover.
What You’ll Need to Install a Replacement Air Filter
- Air Filter (Mower Specific)
- Screwdriver Set
- Shop Rags
Service the Carburetor
The next item on the list is adjusting the carburetor air-to-fuel mixture screw. This is the small screw on a lawn mower carburetor labeled “mix.” Unfortunately, this option isn’t available on all lawn mowers. But if yours does, then you’ll be able to adjust the screw between rich and lean. So, you’ll be aiming for a midpoint between the two.
Here’s a quick table showing you what you should be aiming for (3 ideal) and where you are starting from (4 lean).
Carburetor Mixture Screw Positions
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| Rough Running | Rich Mix | Ideal | Lean Mix | Rough Running |
Steps to Adjust a Lawn Mower Fuel Mixture Screw
- Make sure that your mower air filter is in good condition with no holes.
- Start your lawn mower engine.
- Give your lawn mower a few minutes to warm up.
- Ensure that the choke is turned off.
- Turn the mixture screw so that the carburetor sits between 1 & 5.
- Continue adjusting until the screw sits between 2 & 4.
Now this can take a bit of time and back and forth. It’s really down to how your lawn mower sounds and performs and reaches a point where it stops having overheating issues. It might take a couple of tries, but you should get it right in the end.
What You’ll Need to Adjust a Fuel Mix Screw
Top Off Your Engine Oil
First, use the dipstick to check your lawn mower’s engine oil level. It’s best to do this when the engine is cool, and the oil is settled in the bottom. If you do it when the engine is running or has just been switched off, you’ll likely get a low reading and probably burn yourself with the hot oil.
Once you have the oil level, you’ll need to add the appropriate amount of engine oil so that the oil sits on the “FULL” mark of the dipstick. I suggest adding just a little oil at a time so that you don’t overfill your mower. If you add too much oil, you will have to drain the excess oil from your mower, as too much oil can damage the engine pretty extensively.
When you are checking the oil level, you’ll be able to check the color of the oil and see if it needs to be changed. So, if the engine oil is dark and old looking, you want to plan to do an oil change ASAP.
Keep the Cooling System Clean
When cleaning the cooling fins on your lawn mower, I suggest removing the engine cover to expose the flywheel where the cooling fins are. Once you remove the engine cover/blow housing, you can use leaf blow or, my favorite, an air compressor with an air gun attachment and blast out any debris. I do this every few months, and also when I’m getting my lawn mower ready for spring or when I winterize my mower. You would be surprised how many times I have found little critters nesting in my mower over the winter. Also, a good habit to get into is blowing into the top of the engine cover between mows. This isn’t as effective as removing the cover, but it keeps the build-up to a minimum. Again you can use either your air compressor or leaf blower to do this.
What You’ll Need to Clean Out Cooling Fins
Check Cooling Fluids
A lawn mower that uses liquid cooling systems typically has a transparent fluid reservoir under the hood, similar to an automobile. If you look at the side of the fluid reservoir, you should see a couple of markings. One should read low, and the other should read full. So, you’ll need to make sure that your fluid is between these marks.
If you need to add additional fluid, I recommend using a specific coolant fluid. While you could use just plain water, in the wintertime, this will freeze and potentially cause damage to your mower. So head down to the auto store and grab some generic coolant. Then remove the cap from the reservoir and add the coolant to the full mark. This will help prevent your lawn mower from overheating in the future.
