Can you use a lawn mower without a gas cap?

No gas cap on lawn mower

You can use a lawn mower without a gas cap. The lawn mower will still operate and allow you to mow your lawn. However, it is strongly advised that you do not operate your lawn mower without a gas cap.

Reasons Not to Operate a Mower without a Gas Cap

You may assume that the gas will stay in the tank without the gas cap as long you don’t hit a big bump or mow on a steep slope. However, even on a flat surface the vibrations from the engine will typically cause gas to spill out of the top of the tank when the gas cap is off. This is particularly true when the gas tank is full.

There are obvious environmental risks involved with spilling gas over your lawn. You are potentially polluting the water table, harming the air, putting wildlife in danger, and more. Additionally, any gas that drips onto your lawn can kill it. Lastly, you run the risk of splashing gasoline into the extremely hot parts of the mower (i.e. the muffler), which can spark a fire or explosion. All around, it is a bad idea to use a lawn mower without a gas cap.

Finding a Replacement Gas Cap

You should find a replacement gas cap immediately to avoid any serious problems. Gas caps are not universal so you will need to buy one that fits your mower model. To find a replacement gas cap, locate your lawn mower model number that can typically be found with the documentation that came with your lawn mower. Google the make and model number of your lawn mower plus “gas cap”. So if you were looking for a gas cap for this Craftsman lawn mower, you would Google “Craftsman 37705 gas cap”. The first page of the Google results show a couple of buying options through Sears and Amazon for a replacement. Some owner’s manuals will list the specific part number for the gas cap, which you can just type into a search engine to find a replacement.

A replacement gas cap will cost about $5 to $10 dollars for a typical 21 inch push or self-propelled lawn mower. Yes, this is not cheap considering what you are buying, but it is well worth the price considering the potential risks to yourself and the environment.


You might be thinking that a little gas spilled is no big deal. However, the EPA estimates that 17 million gallons of fuel are spilled annually by individuals who are refueling lawn equipment. This is more than the infamous Exxon Valdez spill that happened in Alaska in 1989, which spilled 11 million gallons into the environment. Most people who have had a decent history of mowing lawns have likely inadvertently spilled a bit of gas. It happens to the best of us. However, there is no excuse for operating a mower without a gas cap. It is probably the last thing you want to spend your money on, but we hope you see the importance of finding a replacement cap after reading this article.