Using Two-Cycle Oil in Lawn Mowers? The Complete Guide

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The two-cycle engine oil is only suitable for use in the single fuel tank of a two-cycle lawn mower. That said, the two-cycle lawn mower isn’t the only mower type out there. If you own a four-cycle mower engine, you might be wondering if your two-cycle engine oil can work on it without any consequences.

Two-cycle oil is not the best fit for a four-cycle engine because the oil burns with fuel and not as a standalone. This means that it will be too light for a four-cycle engine. The design of four-cycle engines means that they often function well with oils in separate tanks or fill ports.

This article covers the basics and everything you need to know about using two-cycle oils in a lawn mower.

Difference Between Two-Cycle and Four-Cycle Engines

There is a significant difference between two-cycle and four-cycle engines. This difference is the chief reason they have different oils, and you shouldn’t try to interchange them.

Two-cycle engines have a single tank that stores a mixture of gasoline and oil to function effectively. While the oil is for lubrication, the gas is for combustion.

On the other hand, four-cycle engines have separate tanks – one for gas and the other for oil.

In terms of mechanics, a two-cycle engine takes two rotations or strokes to round up its piston’s combustion and exhaust cycle. On the other hand, a four-cycle engine will take four strokes to do the same – hence the need for a separate oil compartment in a four-cycle engine. 

Two-cycle engines are gradually becoming less popular as four-cycle engines are proving to be more efficient while working perfectly under varying temperatures. 

If you purchase a lawn mower today, there’s a high chance it’ll be a four-cycle engine. That said, you can request a two-cycle engine if you prefer it. 

Difference Between Two-Cycle and Four-Cycle Oils 

Multi-grade oils with a viscosity of 30 are the best for four-cycle mower engines. 

These oils are suitable for hot and cold temperatures as they retain their thickness while the temperature fluctuates. They do this due to additives like detergents in their chemical compositions. 

On the other hand, two-cycle engines mostly use single-grade oils that are effective at warmer temperatures alone. 

Single-grade oils are also known as small-engine oils and are suitable for engines like weed eaters, chainsaws, and two-cycle mowers. 

When you use these single-grade oils in four-cycle engines, they’ll be too thick at lower temperatures or too thin at higher temperatures. Thus, they cannot provide adequate lubrication in these conditions.

Infographic about the numbers on oils

I’ve written an in-depth article about what oils you can use in your lawn mower, head over there if you want additional information.

What Happens When You Use Two-Cycle Oil in a Four-Cycle Engine 

There are a few consequences to using two-cycle oil in a four-cycle engine. These include:

Wear, Tear, and Permanent Engine Damage 

Two-cycle oils have a limit to how they function at high temperatures. On the other hand, four-cycle engines can work without a hitch as temperatures increase. 

So, using two-cycle oils to lubricate them will cause the oils to thin out and start evaporating as the temperature increases. 

While this might seem harmless, it can actually lead to wear and tear of your four-cycle engine parts. Four-cycle engine parts do not have high-level tolerance for extreme temperatures, and two-cycle oil forces them to work in conditions they are not suited for.

In worst cases, two-cycle oils will permanently damage your four-cycle engine since they can’t prevent excessive friction over time. 

Leads to Leakage in Older Engines 

Using a two-cycle oil in an old four-cycle engine will cause the oils to start squirting from the exhaust system. Since the mower engine will be old and worn, and single-grade oil gets lighter with temperature, it will end up flying out from the exhaust. 

Also, the oil typically combusts with fuel and won’t be efficient in recycling alone in a single compartment. 

Leads to a Hotter Engine 

A two-cycle oil in a four-cycle mower engine will not only lead to wear and tear over time but will make the engine hotter. 

Two-cycle oils become lighter as temperature increases (which is normal when running your engine). This will cause your engine’s moving parts to run faster than normal, thereby increasing the engine’s temperature. 

What To Do When You Accidentally Use Two-Cycle Oil on a Four-Cycle Engine?

Sometimes, you can mix things up by accident and have a two-cycle oil in your four-cycle engine. There’s no need to panic as the damage won’t be instant. 

Two-cycle oils have high lubricant properties that make them effective when mixed with gasoline inside lawn mower tanks. Using them in a four-cycle engine can lubricate the engine’s parts for a while and prevent friction before they begin to thin out.

However, it’s still a risk you don’t want to take.

If you accidentally use two-cycle oil in a four-cycle engine, drain out the oil and add the suitable four-cycle multi-grade oil. If you live in a region with moderate temperatures, you may not have any issues using the oil for a short while. 

However, if you stay in a region with extreme temperatures, a two-cycle oil will eventually damage your engine on frequent usage. Hence, drain out the oil and add the suitable option. 

Is it Bad to Use Four-Cycle Oil on a Two-Cycle Engine? 

It is bad engine maintenance to reverse the roles of machine oils. You should only use four-cycle oil for a four-cycle engine and two-cycle oil for a two-cycle engine. 

If you use a four-cycle oil for a two-cycle engine, the multi-grade motor oil will dissolve in the gasoline to form a uniform mixture like a two-cycle oil. It will also work effectively in a two-cycle mower engine for about an hour or two.  

However, there’s no guarantee that the engine will be healthy afterward. Also, expect a lot of carbon deposit on the plugs and moving parts since the four-cycle oil won’t combust alongside fuel like a two-cycle oil. 

How To Tell if Your Engine Is Two-Cycle or Four-Cycle 

You can distinguish a two-cycle engine from a four-cycled one by the number of fuel tanks or fill ports you can see. A two-cycle engine will have a single fuel tank, and you can tell by the fuel and oil icon on the tank’s cap. 

For a four-cycle engine, you’ll find two tanks or fill ports. One has the icon of a fuel can, and the other has the icon of an oil gallon.

Getting the Right Oil to Fuel Mix Ratio

As you know, a two-cycle engine has a single fill port containing a mixture of fuel and oil. 

Since there’s a mixture, you have to get the perfect mixing formula to avoid adding less of the oil. Also, you’ll have to mix the oil and fuel before filling the tank with it and not mix them inside the tank. 

There are two main mixture ratios – 40:1 and 50:1 – that are commonly used today. 

The 40:1 implies that for every one gallon of gasoline you add to the engine, mix it with 25 ml or 3.2 oz of two-cycle oil. 

And for the 50:1, mix every liter or gallon of gasoline with 20 ml or 2.6 oz of two-cycle oil. The lower the mix ratio number, the more oil you should add to the engine. 

However, these mix ratios vary according to the age of the lawn mower or production year. There are two age categories to keep in mind when considering the adequate mix ratio for your two-cycle lawn mower. 

  • For a two-cycle lawn mower manufactured before 2003, the most suitable mix ratio is 32:1, which is one gallon of fuel and 4 oz (31.25 ml) of the two-cycle engine oil. 
  • For a two-cycle lawn mower manufactured after 2002, the most suitable ratio is 40:1, which, as mentioned above, works out to one gallon of fuel and 3.2 oz (25 ml) of two-cycle engine oil.

If you are not sure of the age of your equipment, you can check the body of the engine, and you’ll find the manufacturing date. If you can’t find it, most lawn mower equipment will work fine if you use the 40:1 ratio without any problems. 

How To Mix Oil and Gasoline 

To mix properly, simply pour the oil into an empty gasoline gallon and add the gasoline to it. Remember to shake the fuel and oil mixture before adding it to the tank. 

You might want to include a fuel stabilizer for the gasoline if you intend to store it for more than four weeks to increase its lifespan. 

You can also get a two-cycle oil that contains a fuel stabilizer to reduce smoke emissions and build-up of carbon deposits on the engine. 


Using the most suitable oil type for your lawn mower is key to extending its lifespan and getting the best performance from it.

Two- and four-cycle engines differ in mechanism, and the oils made for them differ in function. Identify the right lawn mower type and use the recommended oils for it.

For a two-cycle engine, you need to mix the right fuel-to-oil ratio according to the age of the lawn mower. For a four-cycle engine, you only need to fill out the oil tank.


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