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Moto Mind
Moto Mind is a technical blog written by Paul Olesen who is a powertrain engineer working in the motorcycle industry. The blog covers a wide variety of topics relating to two and four stroke engine performance, design, and optimization.


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Filling Up At The Pump

Posted by Paul Olesen , September 21, 2015 · 12,047 views

Filling Up At The Pump

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.

 

Fueling Tip
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!

 

Book News
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!
-Paul

 

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cjjeepercreeper
Sep 21, 2015 02:08 PM

"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."

 

Yep, been doing that for years.  SOP.

Up here in Canada the only gas station that has a separate pump for premium (94 octane) is Chevron, so thats what we use. Good practice to use though if I ever get caught somewhere where they only have 93 on a shared pump. 

    • Paul Olesen and TeamTwoWheels like this
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Good practice.... I do it as well, except when I forget to drive the wifes car and end up at the pump, gas can in hand, and realize I drove the diesel. :) 

I burn ethanol free fuels in all our bikes and seasonal gas motors (lawn mower, edger etc) so if they do happen to sit for a period of time, you dont end up with a bunch of white residue in the carb causing the problems.

 

You can find gas station that use ethanol free fuels either on their website http://pure-gas.org/ , on there website there are the links for the APPLE or GOOGLE store for your smart phone.

    • nofrillls and Event Horizon like this
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i find it hard to believe that its only a third of a gallon left in the hose, ive been fueling the truck for years before putting it in my can but i like to run at least four gallons into the truck first

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Paul Olesen
Sep 27, 2015 05:43 PM

Good practice.... I do it as well, except when I forget to drive the wifes car and end up at the pump, gas can in hand, and realize I drove the diesel. :)

Yes, definitely don't want to fill the diesel up with gas!

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Paul Olesen
Sep 27, 2015 05:44 PM

I burn ethanol free fuels in all our bikes and seasonal gas motors (lawn mower, edger etc) so if they do happen to sit for a period of time, you dont end up with a bunch of white residue in the carb causing the problems.

 

You can find gas station that use ethanol free fuels either on their website http://pure-gas.org/ , on there website there are the links for the APPLE or GOOGLE store for your smart phone.

Thanks for sharing the link!

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Paul Olesen
Sep 27, 2015 05:47 PM

i find it hard to believe that its only a third of a gallon left in the hose, ive been fueling the truck for years before putting it in my can but i like to run at least four gallons into the truck first

I do too, but unfortunately I didn't uncover any other studies or info stating differently so I had to run with it. 

I figure that if you are that close to the edge with detonation then you have no business refueling at the pump.

I am probably just as OCD, (or worse) not only do I donate that fuel to my truck (I don't own a diesle so no worries there) I add seafoam to every 5 gallon can I fill. In addition, I also add Sunoco 112 premium 1g:4g pump in a 5 gallon can every three cans I fill to add a little lead to the life of the motor. Do this in both of my 2T and 4T bikes. In addition LOL, on any of my 2T bikes, and cans, I shake the hell out of them before I start the bike or pour the fuel. Is that separation anxiety or OCD? 

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mountainman38
Oct 04, 2015 02:16 PM
All you guys spending so much time worrying over the octane rating of the fuel you put into your bikes must not know that the energy yield of gasoline is not related to its octane rating. Octane is added to fuel to reduce pre-ignition (the job previously done by adding lead to fuel), which means that unless your bike has an ECU that can adjust the timing, you're completely wasting your time (and money) with higher octane. Seat of the pants feelings that "my bike is waaayyy faster with Supreme gas!" don't work as data. I always run 87 Octane fuel in my XR600, and it runs great.
What do you guys know about Star Tron "Fuel Enzyme Treatment"? Is it a valid option to eliminate the ethonol in today's gas? I'd be curious to get everyone's input!

I had no idea you guys had one hose for many fuels.  Here in Australia each pump has a separate hose for each fuel, so one pump may have four hoses; diesel, unleaded, 95RON and 98RON. No contamination issues here.

I was pleasantly happy to see this article because back when it became popular for gas stations to use only one hose for all three octanes, I knew I was losing out on the performance deal unless the previous customer happen to purchase premium.  Not likely though.....

But then everything got even worse when ethanol was introduced.  Now not only do I have diluted octane fuel but crappy fuel which is constantly clogging up my carburetor.  Thank you EPA.

All you guys spending so much time worrying over the octane rating of the fuel you put into your bikes must not know that the energy yield of gasoline is not related to its octane rating. Octane is added to fuel to reduce pre-ignition (the job previously done by adding lead to fuel), which means that unless your bike has an ECU that can adjust the timing, you're completely wasting your time (and money) with higher octane.

Seat of the pants feelings that "my bike is waaayyy faster with Supreme gas!" don't work as data.

I always run 87 Octane fuel in my XR600, and it runs great.

.

Hello...did anyone see this? You guys that think premium gives you "more performance" crack me up. Keep obsessing over the 1/3 gallon in the hose lol. Unless your bike calls for higher than 87, or is old enough to have carbon buildup on the Pistons effective increasing your compression ratio, paying for gas above 87 octave IS NOTHING BUT A WASTE OF MONEY!!
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mountainman38
Oct 06, 2015 08:07 AM

Jason,

 

You can't preach to the converted.

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bazza400wondai
Oct 13, 2015 02:57 AM

yes i was once like all of you only 95 premium for me ,But then i started trying anything i could get 92,95 even 98

when i could find it out here (rural Australia) E10 yes ran it much difference ? yes mainly in economy K's per tank

not to worried now as long as im riding im happy. 

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MrN2OBelvedere
Nov 12, 2015 01:47 PM

. Hello...did anyone see this? You guys that think premium gives you "more performance" crack me up. Keep obsessing over the 1/3 gallon in the hose lol. Unless your bike calls for higher than 87, or is old enough to have carbon buildup on the Pistons effective increasing your compression ratio, paying for gas above 87 octave IS NOTHING BUT A WASTE OF MONEY!!

 

Sorry to say it, but modern bikes run way higher compression than that old xr600. Detonation is a very real thing and premium fuel will help avoid damage. Sure, you don't need race fuel for your lawn mower or trail bike, but for a modern bike it is recommended.

About Paul Olesen

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