What Happens If You Put Mixed Gas In a Lawn Mower?

You’ve just bought a lawnmower to keep the grass in your lovely garden mowed. Wondering if you can run your lawnmower on mixed gas? It’s better to not do so.

So what happens if you put mixed gas in a lawn mower? 

Well, for starters, it actually depends on the engine. If your lawnmower has a 2 stroke engine, it’ll be fine. If your lawnmower has a 4-stroke engine, mixed gas can cause a lot of problems. Your mower might get overheated and clogged, the oil might be stuck in the fuel line. The engine might start to smoke. 

So what do you do now? First, find out what kind of engine you’re using. We’ve written in detail about oil suiting types of engines. Start reading! 

What Happens If You Use Mixed Gas to Your Lawn Mower Engine?What Happens If You Put Mixed Gas In A Lawn Mower

The engine in your lawn mower can be either a 2 stroke engine or 4 stroke engine. Mixed gas can affect a 4 stroke engine but it won’t affect a 2 stroke engine. 

2 stroke engine does not require a separate oil intake. You just need to purchase one type of gasoline that is already mixed with oil.

In a four-stroke motor, fuel and oil must be added individually. But you have to buy the Fuel and Oil for the engine separately.

1. Mixed Gas in 2-Stroke Engine 

Gasoline is used as a lubricant in two-stroke engines. So, the oil must be blended in with the fuel.

Aside from that, a two-stroke engine runs on ordinary gasoline with a small quantity of oil added. The fuel is used for combustion and the oil is used for lubrication.

Here are some 2 stroke engine oil we recommend-

You can use your choice of oil for your two-stroke engine. And be sure of no damaged engine.  

2. Mixed Gas in a 4-Stroke Engine 

It might cause the engine to choke, overheat, and smoke. Before you start a 4-stroke engine, drain the mixed gas and don’t forget to replace it with the proper gas for the 4-stroke engine. 

Clogging and Overheating

Oil combined with gasoline can clog up four-stroke engines. This causes overheating because they are designed for greater tolerances.

Smoke from Exhaust 

It is feasible to operate a four-stroke engine on the two-stroke fuel you’ve prepared. However, with time, this might result in oil smoke from the exhaust or foul plugs in the 4 stroke engine.

If you unintentionally spill oil into the gas tank due to mixed fuel, the mower will not be damaged. Nevertheless, you will need to drain the tank and reload it with gas before using it.

Here are some oil we recommend for 4 stroke engine- 

Combustion and Explosion

But if you keep on mixing oil and fuel, the engine will be damaged more quickly. Adding oil causes more wear and tear on the cylinder liner and piston, as well as damage to the piston.

There will be anomalous combustion, banging, and explosion as a result. 

So, while mixed gas is great for a 2-stroke engine, it is not ideal for a 4-stroke engine. However, you might have already accidentally poured some mixed oil in the gas tank.

We’ll show you how you can prevent these mistakes in the future.

How Do You Prevent Lawn Mower Gas Problems?

There are some ways you can prevent your lawnmower gas problems. Especially if you can spot the problems beforehand. We enlisted the factors you need to consider, so give it a read: 

Understand the Difference Between the 2-Stroke and 4-Stroke Engine

The following characteristics can help you distinguish between the two engine types.

You have a 2-stroke engine if you see only one fill port for both the engine oil and gas.

You have a 4-cycle engine if you can see two different fill ports, one for gas and one for oil. In these engines, never put oil and gas together. 

Understand the Difference Between Mixed Oil And Regular Oil 

You can easily differentiate between the two kinds of gas.

Simply take a piece of white paper and then dab it with a drop of gasoline. Allow the gas to evaporate. The paper will dry fully if it is simply gasoline. Only gasoline means the gas is unmixed.

If there is oil in the gasoline, there will be an oil stain on the paper after it has evaporated. This is because of the lower boiling point of the gas, so the gas evaporates first.

Choose the Best Fuel for Your Lawn Mower Engine

The best suitable for lawn mower engines are fresh clean gas. The gas should have an octane rating of at least 87.

Higher octane ratings are suggested at high altitudes.

It is acceptable to use gasoline that contains up to 10% ethanol or up to 15% Methyl Tertiary Butyl Ether. You should avoid using gas that has more than 10% ethanol.

Here are the gas containers we recommend- 

Well here are the problems your lawn mower engine can have due to mixed gas. The good news is you can prevent them before they damage your engine long-term. 

Frequently Asked Questions

Question: What will I do if the oil clings inside the tank?

Answer: Once the oil has drained by tilting the tank, combine and swirl some dishwashing detergent with warm water to rid of any oil that has clung to the tank walls.  

Question: What are the signs of contaminated fuel? 

Answer: Fuel contamination includes causing the engine to crank but not start, operating unevenly or losing power, dying while in operation, and excessive smoke.

Question: What will I do if the oil gets stuck in the fuel line?

Answer: Most likely, the oil is in the fuel line and priming pump. Remove and replace the gasoline line in this situation. 


I hope you got your answer to the question, what happens if you put mixed gas in a lawnmower. So, be aware of what kind of engine and fuel you’re using. 

If you have any more questions, feel free to contact us. Take care!

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