By: Author John Cunningham. Published: 2023/07/20 at 2:51 pm
Shut her down…she’s going to blow! A hot running saw is a point where it’s doing damage and the kind of damage that’s super spendy to fix. But let’s not assume the worst just yet; let your saw cool, and we’ll get this figured out.
Chainsaws can overheat, and the top six reasons they do include:
- Excessive use
- Dull chain
- Bar lube issue
- Lean carburetor
- Cooling system clogged up
- Weak gas mix
In this post, we’ll cover chainsaw overheating signs, what happens if you ignore them, why saws overheat, the diagnosis, and the fix; let’s dive in.
- What are the signs of overheating?
- What happens when saw overheats?
- What causes a saw to overheat?
- How to prevent overheating
Signs Your Saw is Overheating
As you’re reading this, I’m guessing you’ve noticed a change in your saws performance, and that’s one sure sign a saw could be overheating. But there are some other clues, too, and they include:
- Smoke – smoke is a pretty conclusive sign your saw is overheating.
- Smells – a scorching smell or a smell that is not unusual when operating your saw.
- Sounds – a ticking sound from your saw. You won’t hear this when it’s running, but you will when it’s switched off.
- Feel – if you get a sense that it feels hotter than usual, you’ll notice it even with gloves on
- Performance – performance issues range from just not having as much power as normal, not restarting when hot, and the pull cord feeling stiff to pull.
What Happens When a Chainsaw Overheats?
Overheating is bad; it typically means the engine is damaged. How damaged depends on how hot the saw got and how long it ran hot.
Overheating is a common problem with 2-stroke machines because they are air-cooled and so rely on airflow around the engine and oil mix in the gas to do the heavy lifting when it comes to cooling.
But as you’ll learn, there are a ton of other factors that will affect our saw’s operating temperature, and we’ll get to them shortly.
So what actually happens when the saw overheats? Broadly overheating fits into four categories if you like, they are:
Level 1 – Mild overheating typically causes the piston rings to score the cylinder wall (just a little) and the piston too. The saw still operates and lives to fight another day; it just isn’t as powerful as it was, but still very useable and nothing to get excited about.
Level 2 is where the rings become so hot they stick inside the piston grooves; here, the saw typically still runs cold but hot… She’s a ballbreaker. It’s possible to replace just the piston and rings.
Level 3 is where the cylinder piston and rings are badly scored, so scored the saw doesn’t have compression. It’s possible to rebuild, but it’s likely not economically smart to do so.
Defcon 4 is where the piston has become so hot it has fused with the cylinder and become one if you like. Useful for keeping the shed door open on a windy day.
Overheating really is a killer of 2-stroke engines. I’ve covered some top tips to help you avoid chainsaw overheating, and you can check that out here.
Next, we’ll look at why saws overheat in the first place.
What Causes a Saw to Overheat?
There are literally dozens of factors that affect the temperature of your saw, and below, I’ve covered all the most common reasons saws overheat and how to diagnose and fix them.
The first common cause is simply overworking the saw; a saw operated at full tilt (about 12,000 RPM) generates a lot of heat. Allowing you saw to rest every thirty minutes of operation for at least ten minutes is good practice.
Another common issue is asking too much from a saw; I know it’s tempting to cut down heavier timber with a hobby saw, but these saws aren’t fit for this type of workload, and the saw protests by overheating.
A dull chain will cause both the operator and the saw to work harder to do the same work. In fact, a dull chain is dangerous as it typically causes the operator to lean harder on the saw. This increases the risk of accidents, but it also increases engine load and friction between the chain and bar.
Some of this heat is transferred to the engine with heat soak.
A sharp chain is easier on man and machine and safer too.
Sharpen regularly and replace before reaching teeth wear indicators.
Bar & Chain Oiling Issue
The bar and chain are as you know equipped with their own dedicated oil system. The oil serves to cool the bar and chain and reduces friction, heat, and the risk of kickback.
Running low on bar oil or oiling system problems will result in increased friction and dull the chain quickly, leading to even more heat, as we’ve covered already.
Common bar oiling issues include:
- Oil quantity adjustment needed
- Using wrong oil type
- Running out of oil
- Blocked oiling bar ports
- Faulty or worn oil pump
Engine Running Lean
Engines don’t run on just gas alone; they need a quantity of oxygen mixed with the gas. The carburetor is responsible for mixing the correct amount of air with the gas. The ratio is 14.7 parts oxygen to 1 part gas.
Now problems arise when the ratio slips to what’s known as the rich or lean side of the scale. Both will cause running issues, but a lean condition is worse as it causes an engine to run hot.
A carburetor can move out of adjustment over time, but ambient temperature, elevation, and humidity also play a part; since cold air is richer in oxygen, our saws will also run leaner in colder temperatures than hotter ones.
Meaning we may need to richen (fatten) our saw up a touch if using it in colder conditions.
I wrote a detailed explanation of adjusting a 2-stroke carburetor using a tachometer and without, and you can check it out here – Carburetor adjustment.
Cooling System Clogged Up
Air-cooled machines rely heavily on the free flow of air across their components to cool it down; an interruption in flow means increased engine temperatures. Air-cooled machines use rotating flywheel fins to pull air in through the recoil assembly vents; they use defusers or a shield and ducting to direct the air around the coil, cylinder head fins, and carburetor.
Air is used to cool but also help direct heavy debris away from the carburetor.
A saws cooling system should get a clean-out once a year with compressed air or improvise a selection of large and small new paint brushes works great when removing stubborn debris.
As saws age, cooling fins can become brittle, bent, or broken; check the engine fins are clean and undamaged and that the side cover vents and ducting are clean and clear and undamaged.
Check defusers are in place; in older saws, they are often seen as surplus when reassembling, but they do serve a purpose.
Weak Gas Mix
All gas-powered chainsaws are two-stroke engines that need oil mixed with gas. Your maker specifies the quantity of oil with gas, and it varies by manufacturer, but if your saw is modern, then it’s likely running a 50:1 for every fifty parts gas; we add one part two-stroke oil.
Older engines could run 40:1 or 30:1.
Manufacturers are particular about the type of oil, too; they will typically ask if we use a two-stroke oil that’s been formulated to work with ethanol fuel. The formulated oil remains mixed with the ethanol and helps reduce gas ethanol separation when left sitting for a period.
Anyhow, the point is the ratio is critical; oil is not only used to lubricate the internal metal components but also keeps them cool and clean.
Running less oil or inferior oil in the mix will mean higher operating temperatures and risks engine damage.
Air Filter Blocked
If our saw can’t breathe, it will run poorly and run hot into the bargain. Saws throw out a ton of debris, and the air filter is in the firing line for a lot of it. Manufacturers recommend we at least check out the air filter for debris before every use.
That may be excessive for the hobby user, but if your saws are doing a lot of heavy lifting, I suggest cleaning every day, and that’s a simple process.
Remove the other shield and blow off the loose debris before removing and cleaning the air filter.
I covered inspecting and cleaning your air filter and you can check that out here.
We’ve covered how cold temperatures paradoxically cause our engine to run hotter because the colder temperatures cause an engine to run naturally leaner with all that extra oxygen around.
But what about hot temperatures? Well, you guessed it, a hot day is going to cause increased engine operating temperatures.
The solution is to rest your saw (in the shade) and rest more often than usual.
Wrong Gas Type
Small engines don’t like ethanol blended gas, there… it’s out there. Ethanol is problematic for almost all small engines. Ethanol goes stale sooner, attracts moisture, and the alcohol content of the fuel attacks small engine carburetor plastics and hoses.
Chainsaw manufacturers recommend a minimum of 89 octane; they will run on E10 but not E15, E20, E30, E50, or E85. Manufacturers say running their saws on ethanol fuel greater than E10 will void the warranty.
Indeed, U.S. EPA makes it illegal to burn fuel with an ethanol content greater than 10% in outdoor power equipment.
Blended gas separates when left to sit for a period, and as the ethanol content is heavier, it sits at the bottom of the tank with the gasoil mix sitting at the top.
Since the fuel pick-up lives at the bottom of the tank, it sucks on the ethanol gas first, causing the saw to get a drink of alcohol fuel without mixing. That’s why manufacturers recommend a 2-stroke oil specially formulated to work with the E10 gas.
That said, many chainsaw manufacturers now offer their own gas for their saws… I think that’s saying something about ethanol and small engines.
Ethanol causes engines to run hotter, and the more ethanol you use, the hotter she’ll run.
A chainsaw has a clutch, surprising, right? I know! Well, it’s not like a car clutch; it’s a lot less complex, but there are similarities apart from the job they do.
A chainsaw chain isn’t connected directly to the engine; that would make pull starting difficult and dangerous and impossible if the chain brake was applied. And so, a simple clutch system is used to decouple the engine from the chain.
A clutch assembly attached to the engine crankshaft rotates with the engine, and a stationary drum with a chain drive sprocket (Rim drive) sits over it. At engine idling speeds, the clutch doesn’t make contact with the drum, but above idle, the spring-retained clutch is thrown outwards (centrifugal force) and forced against the drum, causing it and the chain to rotate also.
Like a car clutch, our saw clutch wears out, and one of the symptoms is clutch slip; and the slip causes heat.
Check your drum for scorch marks, and check if your chain stalls easily when cutting; both are signs of a bad clutch.
But before condemning a clutch straight off, it is worth checking if there’s a reason the clutch may be slipping, such as an unseated or wrong chain pitch or partially seized bar sprocket, etc.
Chain Brake Issue
The chain brake is a safety assembly that helps stop the chain from rotating in case of an emergency.
The brake employs a metal band and a spring-loaded trigger built into the hand guard. The metal band is positioned around the rotating clutch drum, and when triggered by the hand guard, the band tightens around the drum stalling the chain immediately.
If the band at rest is too tight to the rotating drum, it causes friction, which quickly transfers to the engine, causing an overheating issue.
Inspect the chain brake and, especially, the metal band for heat discoloration; your plastic cover may also show signs of melting. Chain brake assembly may be bought as a complete assembly.
Blocked Spark Arrester
A spark arrester is fitted to outdoor power equipment to help prevent hot embers from leaving the exhaust and causing a fire hazard. A mesh screen fitted over the exhaust muffler exit pipe catches them.
Over time, as you can imagine, these screens become caked in soot and need to be cleaned. Typically, they should be cleaned every 50 hours, but they are often forgotten until, of course, the saw protests.
Overheating is one such symptom, so too is a saw that sounds unusually quiet or a saw that won’t rev up.
Anyhow, cleaning solves this problem, and I’ve covered that previously, and you can check that out here.
You already know air-cooled saws are at risk of overheating by nature. Many factors affect their operating temperature. Engine wear is just one of them; as an engine wears, its internal components make more contact for longer, making more heat.
More heat means more wear; it’s a vicious circle, and components like pistons, rings, crankshaft bearings, and wrist pins wear out and begin to break down. Heat is a by-product.
Chainsaw Overheating Prevention Tips
I’ve been a mechanic for over twenty years, and if I’ve learned anything about equipment, it’s this – taking time and care to do even basic maintenance does pay off.
- Chain – Keep that chain sharp; a sharp chain is less work for the engine and the operator and less friction on the bar.
- Bar oil – Use proper chain oil; avoid these YouTubers that say you can use waste engine oil. Chain oil is sticky and remains on the chain for longer, reducing leaks and friction.
- Air filter – a clear, clean airway helps our engine breathe when on full song.
- Breaks – take a break every thirty minutes or so and more if the temperatures are higher than normal.
- Gas – Use premium gas and oil mix and never stray from the specified ratio.
- Cooling system – Clean the cooling system manually or more often if needed.
Chainsaws overheat for several reasons:
- Excessive use: Running the chainsaw continuously without breaks.
- Dull chain: A dull chain increases friction, making the engine work harder and generating more heat.
- Bar and chain oiling issue: Insufficient bar oil or problems with the oiling system can lead to increased friction and heat.
- Lean carburetor: An improperly adjusted carburetor can cause the engine to run hotter.
- Cooling system clogged up: Blocked cooling fins can reduce airflow and cooling efficiency.
- Weak gas mix: Using the wrong fuel-to-oil ratio or low-quality fuel can lead to higher operating temperatures.
To prevent overheating, it’s essential to maintain the chainsaw properly, including keeping the chain sharp, using the right fuel mix, ensuring proper lubrication, and cleaning the cooling system regularly. Additionally, taking breaks during prolonged use and operating the saw within its capacity can help prevent overheating issues.
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.