Some Considerations When Refueling Your Lawnmower

Today I’d like to briefly discuss a property of gasoline that may not be commonly understood. That property involves the changeable volume of gasoline based on changes to its temperature.

Most people are aware that the liquid in a thermometer expands and contracts based on the surrounding temperature. Like the liquid in a thermometer, gasoline will also expand or contract with changes in temperature. I’m sorry to say that I have learned this lesson - and then re-learned this lesson - on several occasions. The circumstances go something like this: I am running gasoline powered equipment. I run out of gasoline. And then, because I am eager to finish the job without having to stop again to refuel, I fill the gas tank of my power equipment too high. I set the fuel can down and reach for the gas tank cap, but before I can actually get the cap on I notice the gasoline continuing to rise and suddenly overflowing the gas tank. My mistake here was not leaving enough room in the tank for the gas to expand. This has also happened to me a couple of times where I had finished securing the gas tank cap and suddenly the gasoline started squirting out the air hole in the center of the cap.

Needless to say, this is a potentially explosive situation. Particularly if the engine you are refueling is very hot. The lessons I learned here are usually spelled out in the Owner’s Manual for any gasoline powered equipment. Most manuals will tell you, “Do not overfill the gas tank when refilling.” They will also mention that refilling an engine that is still hot should be avoided. And most power mower manuals will recommend that you not refuel the mower while it is still on the lawn. (Any gasoline spilled on the lawn will not explode but it will definitely kill the grass.) And, of course, due to the explosive nature of gasoline when ignited, it is a very bad idea to refuel power equipment if there are any nearby sparks, flames or burning cigarettes.

Finally, if you are using any two-cycle engines (be it a mower, weed-whip or blower), I highly recommend: 1) storing your two-cycle gasoline mixture in a clearly identifiable gas can, and 2) that you do your mixing as soon as possible after refilling that gas can. If you do not have a clearly marked two-cycle gas can and you mistakenly refill your two-cycle engine with straight unmixed gas, there is a very good possibility that your two-cycle engine will overheat and be destroyed in short order. And the reason I suggest mixing your gasoline as soon as possible (meaning at the gas station) is that way you are not apt to forget that the gasoline needs to be mixed before it can be used in a two-cycle engine.

In summary, always read, understand and follow all the safety precautions in your power equipment manual. Remember when you are refueling that one gallon of gasoline has the explosive power of several sticks of dynamite.

NEXT TIME: Not All Grassy Weeds Are Crabgrass