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What happens if You Put Mixed Gas in a Lawnmower?

You have just used mixed gas from one of your other garden power tools in your lawnmower and are wondering if this is bad. Or you just purchased a new mower and are only interested in the question of whether they can use mixed gas in a mower or not. And if using mixed gas would be harmful to the engine.

What happens if You Put Mixed Gas in a Lawnmower:

What happens with your lawnmower if you put mixed gas in it depends on the type of engine. If your lawnmower has a 2-stroke engine, it needs mixed gas, so you are ok. If your lawnmower has a 4-stroke engine and uses mixed gas, it can cause the engine to choke, overheat, and cause the engine to smoke. In the case of a 4-stroke engine, it is best to drain and replace the mixed gas with the correct gas before starting it.

A typical 2-stroke engine makes one rotation for every explosion. 2-stroke engines have fuel and oil mixed, fuel for the combustion, and Oil for the lubrication. Therefore, you don’t have a separate oil inlet on the machine, and you only need to buy one type of fuel which is already mixed with oil. In the case of a 4-stroke engine, two rotations are made for every explosion. Fuel and oil need to be added separately in a four-stroke engine (not in any fixed ratio), but you will need to buy the Fuel and Oil separately.

In the case of a 4-stroke engine, fuel and oil must be added separately. If you accidentally pour oil into the gas tank (like with mixed fuel), it will not damage the mower, but you would have to drain it and replace it with gas before using the mower.

Two-stroke Fuel in a Four-stroke Lawnmower?

There is no principle difference in gasoline type between “2-stroke” and “4-stroke”. Two-stroke engines use the fuel as a lubricant too, so the oil has to be mixed in with the fuel. Since four-stroke engines are made for higher tolerances, having oil mixed with the fuel can choke them up and cause overheating.

Besides the above, a two-stroke engine uses regular gasoline with an added amount of oil. It is possible to run a four-stroke motor with the fuel you’ve mixed for a two-stroke one. But this will cause oil smoke from the exhaust or foul plugs over time. Another key thing to keep in mind is that you must never try to run diesel fuel in a gas engine or vice versa.

Does Your Lawnmower Need Mixed Gas?

Most four-stroke engines require fresh unleaded gasoline with an octane rating of 87 or higher. You can use gas with ethanol, but more than 10 percent of ethanol is not recommended at all. In comparison, mowers with two-stroke engines use that same type of gas but with high-quality two-cycle engine oil added to it for lubrication. So, yes, the mixed gas is the best choice for a 2-stroke engine but not preferable for a 4-stroke engine.

No separate Oil in 2-stroke fuel:

Gasoline not mixed with oil is not recommended for a 2-stroke engine because running a two-cycle engine with too little oil can destroy the unit. Oil helps cool the piston and cylinder by keeping them lubricated at all times in the cycle. Without lubrication, the metals can melt and potentially grate against each other, transferring metal to and from one another and permanently distorting them.

The ratio of oil in the fuel oil mixture for a 2-stroke engine is not much. The preferred ratio is 40 parts of gas to 1 part of the oil in the mixture.

Fuel for a Four-stroke Engine:

A four-stroke engine uses regular gasoline, like your car (which also happens to be a four-stroke engine), while the oil is injected from a separate reservoir. This eases the burden of fueling the engine up.

Difference between 2-stroke and 4-stroke oil:

As far as the application is concerned for the two engine types, the fuel-oil mixture is used in a 2-stroke engine while you pour oil into a separate port with a 4-cycle engine.

If we are talking about the type of oil, 2-cycle Oil is lighter because it burns with the engine’s fuel, and therefore it also contains certain additives for better combustion.

Recognizing Mixed Gas from Regular Gas:

You can differentiate between the two gas types quite easily. Just take a piece of white paper, and put a drop of the gasoline on it. Then let the gas evaporate. If it is gasoline only (unmixed), then the paper will dry completely. If there is oil mixed in it, you will have an oil spot remaining on the paper after the gasoline has evaporated. This is simply because the gas evaporates first because of its lower boiling point.

What is the Best Gas for a Lawnmower?

Such an important question, isn’t it? You can use gas from any company but have to take care of a few important things. The gas that you intend to use for your mower should tick the following criteria:

  • Fresh: the gas should be clean and fresh.
  • Octane Rating: Should have a minimum of 87 octane number. Higher octane ratings are recommended for use at higher altitudes.
  • Ethanol: Gasoline with up to 10% ethanol or up to 15% Methyl Tertiary Butyl Ether is acceptable. Never use gas with more than 10% ethanol.

How do I know if my lawnmower is 2 or 4 stroke?

You can differentiate between the two engine types based on the following characteristic:

  • If there is only a single fill port for both the engine oil and gas, you have a 2-stroke engine.
  • If the engine has two different fill ports, one for gas and another for oil, you have a 4-cycle engine. Never mix oil and gas in these engines.

Disadvantages of Gas with More than 10% Ethanol:

E10 fuels are approved for usage in lawnmowers. Gas with a higher percentage of ethanol is not recommended. This is because ethanol will absorb water from the air over time, leading to rusting and corrosion, leading to poor performance. Regular gasoline absorbs 50 times less water than E10 gas.

Gas for Small Engines:

The 2-stroke or 4-stroke engines of lawnmowers are regarded as ‘small engines.’ Ethanol-free gas is best for small engines. Non-ethanol fuel is much less harmful to the engine as compared to ethanol-blended fuel. This is because non-ethanol fuel is not as susceptible to condensation, corrosion, and rust. Most non-ethanol gases are rated at about 89 octane rating, which is good enough for small engines. The reason for using ethanol in gas is because it makes the fuel friendlier for the environment.

High Octane Gas for Small Engines:

Engines with low compression ratios are less likely to benefit from anything unusual in the gas, like a higher octane rating. Some fuels may make your engine harder to start. So, you can use regular gas if you don’t want to spend extra money when your engine can’t even take advantage of it.

How to Check the Gas Quality in Your Lawnmower?

The easiest way to check the gas in your engine is to smell the gasoline. Oxidized gas has a strong, pungent smell and is much stronger smelling, unlike fresh gas. The other method is to drain a sample from your machine’s fuel tank or your gas tank into a clear see-through container. If the gas is dark-colored, it has more than likely gone bad.

If you are using mixed gas in your 4-stroke mower, it will show signs of trouble. Oil smoke is the clearest symptom associated with oil burning in a 4-stroke engine. 

Related Questions:

● What are E0 and E10 Fuel?

E10 is a gas with only 10 percent ethanol. E15 is gasoline with 15 percent, and E85 is a fuel that may contain up to 85 percent of ethanol. The ethanol content of most of the general-purpose gasoline sold worldwide does not exceed 10% by volume. All gasoline engine vehicles can use E10.

● How long does gas stay good in a lawnmower?

Depending on the gasoline formula, this degradation can occur in as little as 30 days, though properly stored gas can sometimes stay good for up to a year and up to three years if treated with gasoline stabilizers.

● Is ethanol gas harmful to lawnmowers?

Fuels with 10 percent of ethanol content are approved for use in lawnmowers. Gasoline blends containing higher ethanol levels are not. Using fuel with more than 10 percent of ethanol can damage your lawnmower engine and may also void your equipment’s warranty.

Final Remarks:

So, now you know,  depending upon the type of engine, you need to select the type of fule (pure or mixed). Selecting the right fuel is important because prolonged use of the wrong fuel in the wrong engine can lead to permanent damage. Mixed fuel is used for standard two-stroke engine lawnmowers, and in the case of a four-stroke engine, Fuel and Oil are added to the engine via separate compartments.