How Residual Pump Fuel Affects Your Fill Up
This week I have a quick tip I want to share with you regarding buying fuel and filling up gas cans for your bikes. I know many of you, myself included, rely on premium grade gasoline dispensed from local gas station pumps to put endless grins on your faces. One of the downfalls of gas station pumps is that fuel from the previous sale is left in the hose. According to the American Petroleum Institute, the amount of fuel left in a gas pump's hose is around 1/3 of a gallon.
Generally speaking, when two fuels are blended the octane rating of the resulting fuel is approximately the average of the two fuels. So if you had a gallon of 87 octane and a gallon of 93 the resulting blend would have an octane rating of 90. I'll be the first to admit that 1/3 of a gallon of fuel added to a two gallon gas can won't have much effect on the octane rating. For those of you that like numbers, 0.33 of a gallon of 87 added to 1.67 gallons of 93 will yield the following octane rating:
0.33 gallon of 87 / 2 gallons = 16.5% of the total mixture
1.67 gallons of 93 /2 gallons = 83.5% of the total mixture
(0.165 x 87) + (0.835 x 93) = 92 octane blended fuel
So in a two gallon can, the octane rating of the fuel has dropped a point due to the 1/3 gallon of 87 in the pump hose. Unless you have a very well developed performance engine, this isn't anything to lose sleep over. I think a bigger reasons to want to keep that 1/3 of a gallon out of your can is due to the possibility of ethanol being in the hose from the previous sale. Many articles can be found outlining why ethanol should be avoided, but the main reasons include part corrosion due to the exposure to alcohol, rubber seals and o-rings may not be compatible with ethanol resulting in swelling and failure, and some plastics deteriorate when exposed to ethanol. Not to mention ethanol contains less energy than gasoline. Again, we're not talking about a large percentage of ethanol in the overall scheme of things but I prefer to stay away from the stuff when I can.
I'm very careful about what I run through my powersport engines. To safeguard against filling up a fuel can with residual fuel from the previous sale, I like to donate the first gallon of "premium" to my vehicle before filling my gas cans. This ensures whatever fuel was in the hose and pump is flushed out and that I'm filling up my cans with premium. If you are borderline OCD about what goes in your engines like I am, you may consider adopting this practice.
I suspect many of you have other tips and tricks regarding fueling. Leave a comment below and share your thoughts and experiences so other motorheads can benefit!
I also wanted to invite you to check out my book on how to build four-stroke engines, which is now officially available in print form. It took a ton of work to bring the print book together and get the right help on board. The project hasn't been easy, but I'm proud to offer this book to you and can assure you it will make a great addition to your workshop. You can learn more about the book by following this link: The Four Stroke Handbook
To celebrate the arrival of the print book, I'm running a sale until the 27th of September offering all versions of the book at a 20% discount. After the 27th the sale will end and the price will go up. If you've got a build coming up now or in the future and are interested in the book, now is a great time to pick up a copy.
Thanks for reading and have a great week!