2 Stroke engines can be finicky. One of the most irritating issues that you can run into is overheating of the engine with no apparent reason. I’ve done a ton of research over the years (as well as tossing a 2-stroke weed eater against a wall in frustration) trying to understand this issue. I hope to save you a ton of time with this short and precise troubleshooting guide.
What Causes A 2 Stroke Engine To Overheat? The most common reasons for a 2 stroke engine overheating include:
- Obstructed or impaired cooling system
- Inadequate or poor quality lubrication
- Insufficient Air Intake
We will walk through each of these so that you can see why they contribute to overheating and how to deal with the underlying issue. There are some engine problems that require either mechanical expertise or professional servicing but these are so common that it’s worth checking them off first to make sure the problem is not something simple that you can fix yourself.
Before we delve into the causes, I want to really impress upon you one important point:
Understand This: Something Is In A Bind
When a 2-stroke engine is overheating, something within the system is in a bind. It may be physical bind such as gears grinding from inadequate lubrication or something less tangible like a clogged air filter. But something is causing the engine to run harder than it is designed to run. That makes the engine get hotter than it is supposed to.
It’s very important that you understand this basic principle. If you can troubleshoot your 2-stroke engine while evaluating “where is it in a bind?” you’ll stand a much better chance of identifying the core issue causing the overheating.
Obstructed Or Impaired Cooling System
Engines generate heat and that heat has to be released. There are essentially two established processes for releasing heat; air-cooling and liquid-cooling.
Here’s a helpful video from YouTube on the differences between air and liquid-cooled systems, along with a few pros and cons of each.
Smaller 2-stroke engines like those commonly found on gas-powered yard tools such as string trimmers are usually air-cooled. They are manufactured with cooling fins that allow for heat transfer away from the engine.
If the fins are damaged or obstructed it can impair the engine’s ability to cool, resulting in overheating.
I’ve seen this issue many times. A dirt bike’s fins caked with mud, a string trimmer’s cooling fins obstructed with wet grass, all causes of overheating due to the engine not being able to displace heat properly.
Fortunately, this is an easy fix assuming the fins aren’t damaged. Simply clean them thoroughly and allow them to air dry while the engine cools down.
The second type of cooling system for 2-stroke engines is liquid-cooling. This is seen more commonly in larger engines. Liquid-cooled systems usually involve a water jacket that encases the engine (specifically the cylinder) to prevent overheating.
Correcting issues with these involves a little more work. First, you have to identify the underlying cause. Is there insufficient liquid to provide cooling? Is there a leak?
So, a little more investigation required on the liquid-cooling systems but ultimately you need to ensure that the supply of liquid-cooling is not being impaired.
Inadequate Or Poor Quality Lubrication
A combustion engine has metal parts that rub together, generating friction and heat. Without sufficient lubrication, overheating can occur.
Improper gas-oil-air mix
Proper gas-to-oil and air-to-fuel mixtures are required for an engine to operate at its optimal performance capability.
If the engine does not have access to adequate amounts of oil, the consistent rubbing of metal will increase temperatures (source). This can be caused by an inappropriate gas-to-oil ratio or a physical leak.
I’m a strong believer in spending a little extra money on premixed fuel to ensure a precise gas-to-oil ratio. And do yourself a favor by skipping the fuel pump and buying ethanol-free fuel. Ethanol is so hard on small engines.
If there is insufficient air in relation to fuel, this causes the engine to run “rich”. That means there is not enough oxygen being provided to burn all of the fuel. The engine runs cooler when the air-to-fuel ratio is rich.
Memory tip: An old mechanic taught me an easy way to remember this years ago and I’ve never forgotten it:
“Being Rich is cool but the air is thin at the top”.
On the other end of the spectrum, when there is too much air in relation to fuel, the engine runs “lean”. It is in this scenario that a 2-stroke engine is prone to overheating. There is too much oxygen being provided. As the fuel is burned, excess oxygen remains (source).
Have a look at this short, very old video on YouTube. A chainsaw was running lean for too long and suffered from a “lean fuel seizure”, literally meaning the piston got so hot that it melted and the engine seized up.
Air and fuel are mixed in the carburetor. Most carburetors have adjustment screws to fine-tune the air-to-fuel ratio. Refer to your owner’s manual for precise instructions.
Insufficient Air Intake
It’s helpful to think of a combustion engine as air-breathing. It has to have a sufficient supply of fresh air. This is provided through the engines air-intake system.
If the air intake is clogged or obstructed, the engine will not be able to get sufficient air in which can result in overheating. This can be caused by a clogged air filter, a foreign obstruction in the intake valve, or any other impedance to airflow.
It’s possible that you’ll notice issues when starting the engine if the air intake is clogged. One symptom is the engine dying when giving it gas. But if the intake for air isn’t completely obstructed, the engine may still run but operate hot due to not having sufficient airflow.
Don’t overlook this seemingly obvious but highly susceptible component in your troubleshooting. It can be a quick and easy fix to replace an air filter or remove a visible obstruction.
Obviously, this is not an exhaustive list of the potential reasons for a 2 stroke engine to overheat but these are the most common causes that I’ve run across and they are easy to check and correct yourself.
A 2-stroke engine is a complex system with multiple potential points of failure. But before you take it in for professional servicing, check these often overlooked causes of overheating.