Can You Put Weed Eater Gas in a Lawn Mower?

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Most of the conventional weed eaters and lawn mowers run on gas. If you have some leftover weed eater gas, it is natural to wonder whether or not you can use it in other tools, such as a lawn mower, and vice versa. So, can you put weed eater gas in a lawn mower?

You can put weed eater gas in a lawn mower if both the tools or their engines run on the same type of fuel. However, you can’t use a 2-stroke weed eater’s gas that’s already mixed with engine oil in a 4-stroke lawn mower. Also, the gasoline grade and condition will matter.

The entire premise boils down to the practical circumstances and the specific type or condition of your weed eater gas, and the specifications of your lawn mower. Read on as I explain how or when you can put weed eater gas in a lawn mower and if it is something you should consider.  

Scenarios When You Can Put Weed Eater Gas in a Lawn Mower

Most weed eaters have a 2-stroke engine. You need gas mixed with the recommended engine oil to run such 2-stroke engines, but many lawn mowers don’t function that way. There are some 2-stroke lawn mowers. However, most lawn mowers have a 4-stroke engine.

A 4-stroke engine doesn’t require gas mixed with oil. There’s a separate engine oil reservoir to lubricate all the moving components. The gas reservoir or tank of a 4-stroke lawn mower has only gasoline or petrol. Thus, any gas mixed with engine oil is unsuitable for such a tool.

That said, if both your weed eater and lawn mower have 2-stroke engines, the scenario is a tad different. You can put weed eater gas mixed with engine oil in a 2-stroke lawn mower, provided the gasoline or petrol isn’t stale or of an inferior grade.

However, if you have a 2-stroke weed eater and a 4-stroke lawn mower, you have to zero in on the type of gas, its grade, and condition. Here are two scenarios when you can put weed eater gas in a lawn mower.

Your Weed Eater and Lawn Mower Run on the Same Type of Gas

Suppose you have weed eater gas that isn’t mixed with any 2-stroke engine oil. You may have this gas in a container or tank. If this gas is of the same grade that your lawn mower runs on, there’s absolutely no problem in using the same fuel in either tool.

Consider the following example of two leading brands:

  • Weed Eater runs on 87 octane gas, which is the regular, unleaded gasoline. This grade is also known as 87 AKI and 91 RON, depending on where you are. This requisite applies to Weed Eater Edgers, Trimmers, etc.
  • Briggs & Stratton recommends the same grade for its lawn mowers, although that is the minimum requirement. The same minimum requirement drops to 85 octane for its lawn mowers at high altitudes, i.e., above 5,000 feet or 1,524 meters.
  • Therefore, if you have regular, unleaded Weed Eater gas that’s 87 octane (87 AKI or 91 RON), you can put that fuel into a Briggs & Stratton lawn mower. However, a few other factors are still in play.

The Weed Eater Gas Is Fresh and Not Mixed With Any Engine Oil

Suppose your weed eater gas is of the same grade as is required for your lawn mower. Plus, the weed eater gas is not mixed with any 2-stroke engine oil. In such a scenario, you may use the weed eater gas for your 4-stroke lawn mower, but only if it is clean and fresh.

Old or stale gas isn’t only bad for your lawn mower. The fuel is also problematic for weed eaters. You shouldn’t use stale gas for either or any other tools, regardless of whether the fuel is mixed with any engine oil or not. Also, the original grade or quality of the gas doesn’t matter if it is bad. 

Thus, you can use clean and fresh weed eater gas in a lawn mower, provided the fuel isn’t mixed with engine oil.

Instances When You Can’t Put Weed Eater Gas in a Lawn Mower

Here are a few instances when you can’t put weed eater gas in a lawn mower:

  • You have a 4-stroke lawn mower and a 2-stroke weed eater’s gas mixed with oil.
  • The weed eater gas is unclean, old, or stale because it was stored for a long time.
  • The weed eater gas contains more than 10% ethanol (gasohol) or other alcohols.
  • The weed eater gas has more than 15% methyl tertiary butyl ether (MTBE).

You shouldn’t use any fuel in your lawn mower that’s not recommended by the manufacturer. The same principle applies to weed eaters, too. The warranty will be void if you don’t follow the recommendations of the manufacturer, including Weed Eater and Briggs & Stratton.

Now, you may not remember whether or not some old weed eater gas is mixed with 2-stroke engine oil and if the fuel is in a usable condition after being stored for a while. In such cases, it is necessary to assess the quality or condition of the fuel and if the gas is mixed with engine oil.

You may use any of the following tests to know if you can use weed eater gas in a lawn mower:

  • Check if the color of your weed eater gas is transparent. Gasoline mixed with engine oil will have a distinct hue: bluish, reddish, greenish, etc. Also, try to conduct this test in a clear container or vessel so that you can have a lucid view of the color of the gas.
  • Smell or touch the weed eater gas to check its condition. Clean and fresh gasoline has a strong odor, and it evaporates quickly, unlike 2-stroke engine oil. Also, old or stale weed eater gas may have condensed water in it, which should be evident when you test. 
  • Use kitchen tissue or paper towel to test for staining. Fresh weed eater gas that isn’t mixed with engine oil won’t leave a colored stain. The tissue or paper might be wet, but it won’t have a greasy stain or residue.


You can put weed eater gas in a lawn mower if the fuel isn’t mixed with engine oil and it’s clean, fresh, and of the recommended grade. Otherwise, you must refrain from using or recycling weed eater gas unless you’re certain that both tools can share the same fuel in the current condition.

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