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Does Lawn Mower Gasoline Expire?

A common question that we in the outdoor power equipment business get a lot is “Does gasoline expire?”

The answer is yes, it does expire and in a shorter amount of time than you think. Unfortunately, once gasoline is pumped at your local gas station you have between thirty and sixty days before it goes bad. Once your gasoline has reached its expiration date it will start to have an adverse effect on your equipment.

Here’s what makes gasoline expire and what old gasoline can do to your equipment.

The reason gasoline expires so quickly now, as opposed to ten years ago, is the introduction of ethanol into the fuel supply. As an attempt to create a more environmentally friendly fuel the EPA implemented ethanol (a form of alcohol derived from corn) which now takes up ten percent of regular 87 octane gasoline.

That was a cost effective and environmentally friendly thing to do, but small engines now suffer because of it. While the fuel that you purchased sits in your garage or shed, the ethanol draws moisture out of the air and waters down your gasoline. This can have negative effects toward small engines like those on lawn mowers and snow blowers.

Putting or keeping old gasoline in your lawn mower can cause a variety of problems. Your mower may not start, run as smoothly, and even sputter or die during operation.

If your machine won’t start due to old gasoline you need to remove the built-up residue that is choking out the engine. Any gasoline still in the tank should be siphoned out. Depending on the type of mower you have and how much built-up residue was present in the gas, you may need to remove and clean the carburetor.

The biggest problem with ethanol gasoline in equipment like lawn mowers is that you only use these machines once a week or so. Thus the potential of gasoline reaching its expiration date while in the fuel tank of your machine grows exponentially. Expired gasoline can damage internal components of your carburetors, deteriorate fuel lines and seals, and cause a varnish build up that could clog small fuel ports which are necessary for your machine to start and run.

Fresh gasoline is essential to the proper starting and running of a machine. With the addition of ethanol to our fuel supply it is becoming more important that you pay attention to the age of your gas, so that can you filled last spring needs to be taken to a recycle center and disposed of properly, because it’s no good and could cause you more headaches than it’s worth.

As a rule of thumb, and to prevent having issues with your lawn mower, run the remaining gas out of the machine or drain the gasoline at the end of each mowing season.

You May Also Enjoy These Articles:

Mower Maintenance

 5 Reasons Pre-Mixed Fuel is Best

How to Store Small Engine Equipment 

How to Replace a Toro Lawn Mower Wheel

How to Replace a Toro Lawn Mower Blade

Why Weingartz?

Weingartz, family owned and operated, began in 1945 as a farm supply store for local Michigan families. In the 1970s, we began to focus exclusively on outdoor power equipment. Over time, we morphed into the “power equipment superstore” that now defines all of our locations. The staff and experts at Weingartz work diligently to provide the best service possible and give honest and helpful advice to each and every customer.

Weingartz also sells parts for all outdoor power equipment at

39050 Grand River Ave.
Farmington Hills, MI 48335
(248) 471-3050

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