Mowing your lawn is a whole workout. You’re out there under the sun, sweating as you go back and forth over the grass, dreaming of a cold drink…
What’s that weird noise coming from your lawn mower?
It happens even to the best of us: a lawn mower overheating. Some key signs include engine smoke, blackened spark plugs, unusual noises, or even the engine locking up.
Common reasons your lawn mower is overheating involve a clogged air filter or cutting deck, low oil levels, blocked cooling fins, or broken engine parts. Or it could just be a really, really hot day.
If your mower’s behaving oddly, and it’s radiating heat like an oven, it may be time to get up close and personal. After it’s cooled down, though!
Signs of a Lawn Mower Overheating
The primary sign is, of course, an overheated mower engine – but it’s not like you can do a quick poke to check.
Lawn mower overheating symptoms include:
- Smoke from the engine
- Blackened or damaged spark plug
- Rattling or other unusual noises
- Decreased performance
- Engine stalling or locking up
If you notice any of these signs – or really, anything out of the ordinary – stop the mower ASAP. If your lawn mower won’t turn off, you may have to use the kill switch or shut off the gas.
Overheating can also cause your mower to backfire when starting. This could be due to the internal parts heating up and igniting fuel prematurely. Alternatively, something internal is causing both the overheating and the backfiring.
Check the owner’s manual before getting your hands dirty. The instructions and specifications will come in handy, especially if you need to buy new parts.
Why You Should Fix Lawn Mower Overheating ASAP
Depending on the cause, an overheated lawn mower could be dangerous. It could cause your lawn mower to malfunction, leading to damage to the machine – and even injury to yourself.
The hot temperatures could lead to melted parts, blown gaskets, or even fire.
Figuring out why your lawn mower is overheating will also help prolong its lifespan.
Why Is My Lawn Mower Overheating? (And How to Fix It)
There are several reasons for an engine overheating. Knowing the cause will help you solve the problem.
The first solution to a lawn mower overheating is turning it off and letting it cool. Leave the machine powered off for at least 30 minutes – never touch a hot mower.
1. Clogged air filter
This is one of the more common causes of engine overheating, especially in walk-behind mowers.
The air filter allows cool air to enter the mower while blocking debris. This cools down the engine and creates the fuel-air mixture that drives lawn mowers.
Over time, dust and dirt will build up on the filter, hindering air intake. And without air to cool the engine, it’ll quickly cause overheating issues.
How to fix:
Easy – clean the air filter! Paper filters just need a good brush-off, while foam filters can be washed in soapy water.
You can also use some compressed air to blow off any debris from the filter housing.
It’s best to clean the filter every few uses to prevent dirt from building up. For disposable models, replace the dirty filter with a new one.
Change the filter every 300 hours of operation (or about once every mowing season).
2. Clogged cutting deck
A lawn mower deck houses the blades. It’s fairly common for the deck to get clogged during use – mowing wet grass is one usual culprit.
(Yes, it is bad for your lawn mower. And also for your patience.)
Other times, if your mower blades aren’t sharp enough, they’ll uproot grass instead of cutting it. That’ll lead to jammed blades and a clogged deck.
How to fix:
Once the mower is off, you can clear the grass clippings and debris from the cutting deck. If your lawn is wet, you just gotta wait until things dry out.
If the blades are the problem, you’ll need to sharpen your lawn mower blades.
Check for damage first, though – if there are nicks or bends, it’s better to change the lawn mower blades entirely.
3. Low oil level
A low oil level – or old engine oil – means the moving parts in your mower’s engine aren’t getting enough lubrication.
That additional internal friction and effort will eventually lead to the engine overheating. It’ll wear the parts out faster, too.
On the other hand, too much oil in your mower can cause overheating too.
How to fix:
Low oil level = top up the reservoir. Old engine oil = drain the engine and replace with new oil. Too much oil = remove oil through the drain plug or an oil evacuator.
Take care to fill the oil reservoir only to the fill line, and go slow! Check the dipstick frequently to make sure you’re not overfilling.
4. Low cutting height
It’s important to set the correct cutting height when mowing grass. Too high and you won’t cut enough, but too low and you could cause your mower to overheat.
Setting the cutting height too low means your engine is doing more work than necessary, so it’s burning more fuel. In less powerful engines, the engine will overheat quickly.
How to fix:
After you’ve stopped the mower, adjust your cutting deck a notch or two higher.
Ideally, you should be cutting grass to 1/3 of its height – anything lower is bad for your lawn’s health.
5. Mower blade issues
Lawn mowers sometimes overheat due to problems with the blades themselves.
Bent, loose, or misaligned mower blades will cause your mower’s engine to use up more power, creating more heat.
One sure sign of a faulty blade is an uneven cut on your lawn. That shows the blades are either shifting in the deck, or they’re bent out of shape.
How to fix:
For a walk-behind mower, tip it on its side to expose the deck. Meanwhile, for ride-on mowers, drop the deck then disengage it from the machine.
Loose blades can be tightened in place, but a bent blade needs to be replaced.
6. Blocked cooling fins
This is a common reason for a ride-on lawn mower overheating. The cooling fins help dissipate the heat from the engine, but over time, they can become blocked or dirty.
Blocked cooling fins quickly lead to high temperatures inside the engine housing.
How to fix:
Carefully open your mower casing and check the cooling fins – they’re usually near the spark plug.
Clear any debris stuck to the fins, such as grass or soil. Then check your air filter to make sure it’s not damaged and letting debris into the engine housing.
7. Low engine power
This sounds a bit absurd, but it does happen – if your lawn mower isn’t running at full throttle, you’re also overworking it.
For ride-on mowers, ensure you’re going within the recommended speed range. A lawn tractor goes between 5–8 km/h (3–5 mph), while zero-turn mowers go between 8–12 km/h (5–8 mph).
For walk-behind models, certain factors can impact your mower’s power. You may be low on fuel or oil, or your engine isn’t getting enough air.
How to fix:
If you’re on a ride-on mower, increase or lower your setting to the appropriate speed.
For gas mowers, ensure you have enough fuel and oil. Electric-powered mowers may have issues with the batteries or cords.
8. Defective lawn mower engine parts
Your engine could be malfunctioning from loose, broken, or worn-out parts.
Some common issues could be:
- Loose or detached screws
- Loose engine guard
- Damaged cooling fins
- Leaky gaskets
- Loose connections
- Improperly attached tubes
How to fix:
Do a thorough check on your lawn mower engine to make sure the parts are in place.
Anything damaged will need replacing ASAP so you can avoid a high repair bill down the road.
9. Overworked engine
Your lawn mower gets tired too! Kind of. Like most machines and appliances, it’s best practice not to run them for too long.
This goes double if it’s a particularly hot day, since your mower will overheat faster.
How to fix:
Mow in intervals! You don’t need to get the whole lawn in one go, especially for larger or overgrown yards.
You can go over your lawn twice or even thrice throughout the week to minimise the impact on your machine.
10. It’s just really hot out
Sometimes, the culprit is just the weather. If it’s too hot outside for you, then it’s too hot for your lawn mower.
How to fix:
Nothing for it but to wait until the temperatures outside cool down.
Generally, it’s best to mow your lawn around mid-morning, after the dew has evaporated but before the sun gets too intense.
Make sure to check what time you can mow the lawn in your state or town – there are often guidelines for the use of power tools!
Lawn Mower Overheating Due to Low Coolant
Some professional-grade lawn mowers use liquid antifreeze or coolant to keep engine temperatures down.
These models have larger engines that have more power, but are heavier and more unwieldy than air-cooled models. They’re also not very cost-efficient for regular homeowners.
If your liquid-cooled lawn mower is overheating, it may be low on antifreeze. Alternatively, there could be clogs in the cooling system – such as the pump, water jackets, or hoses.
Tips for Proper Lawn Mower Maintenance
All lawn mowers need to be maintained over their lifetime. Follow a regular maintenance schedule to ensure every part of your mower is in proper condition.
Doing a quick check before you start it up could save you a headache later.
Clean, fix, or replace any components affected by the lawn mower overheating. Never run a mower with clogged or broken parts – you’ll put yourself and the machine at risk.
Winterise your mower properly to minimise any damage throughout the colder months, when it’s not in use.
If you can’t figure out what’s causing your lawn mower engine to overheat, it’s time to talk to a professional!
