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Discussion Starter · #1 · (Edited)
On average how much fuel is trapped within the gasoline pump hose ?

Here is why I ask:

On the way to the track today, after I got off the freeway (about 35 miles from home), I filled up my bike before entering the track. The problem is that I only put in about 0.9 gallons of gasoline. So I started to think, what happens if there is more than 0.9 gallons of gasoline trapped in the hose and if the person using that same hose ahead of me was pumping 87-octane gasolines, then I just pumped 0.9 gallons of 87-octane gas into the tank of my gixxer which specifies 90-min octane !!!

In this case,that wasn't much of a problem because I left home with a full tank of 109-octane race fuel, so in the worst case, I get about 104-octane average.

However, for my normal canyon runs, I use 91-octane (the highest we can get at most places in California), so if I mix 0.9 gallons of 87-octane gas with 3.6 gallons of 91 gasoline, that averages out to only 90.2-octane, barely meeting the minimum requirement. This means that I gotta plan my fueling carefully and stop doing these 1-gallon fill-ups so that I don't keep pumping 87-octane gas into my tank.

Is there anyone who would know how much fuel is trapped in the gas pump hose ?

Thanks in advance.
 

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If you pump the left over .9 gal of 87 octane on top of your 3.6 gal of 91 octane, you get the same mixture as if you started with an empty tank.

If the tank is empty, you put .9 gal of 87 octane in before you start getting the 91 octane, than continue to put another 3.6 gal of 91 octane in. Same mixture.

It doesn't matter what amount you put in, you still wind up with the same mixture.

The only way to be sure, is to follow someone that pumped 91 octane.
 

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Ah, I love Switzerland. Most of our stations have 3 hoses on each pump - one for regular, one for super, and one for diesel. No mixing of fuel in one hose, exactly for the reasons mentioned by wookie!
 

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Rickster said:
If you pump the left over .9 gal of 87 octane on top of your 3.6 gal of 91 octane, you get the same mixture as if you started with an empty tank.

If the tank is empty, you put .9 gal of 87 octane in before you start getting the 91 octane, than continue to put another 3.6 gal of 91 octane in. Same mixture.

It doesn't matter what amount you put in, you still wind up with the same mixture..
Unless he does multiple 1 gal fill ups in a row.

Ah, I love Switzerland. Most of our stations have 3 hoses on each pump - one for regular, one for super, and one for diesel. No mixing of fuel in one hose, exactly for the reasons mentioned by wookie!
We have some of those too, but they are slowly going the way of the dinosaur.
 

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LOL - this thread reminded me of something I used to do when I was young. When I read the topic, I thought it was going to be the same thing. Sorry if I hijack the thread a little.

The hoses tended to always have a good bit of gas left in them after the stations closed, so we would go to each pump, and just drain what was in the line into our tank by shaking the hose. After we did this several times, we'd have enough gas to cruise for several hours - for free. We did this on a regular basis.

I'm not sure if you could do something like this today, but if you could, you'd save quite a few $$.

Back on topic though - if it bothers you about getting the mixed octane, then try to get behind someone that you pretty well believe will get the good stuff, and just wait on them.
 

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You worry for nothing- I managed a C-store back in the 1980s, and the dealer where I managed the service department had a gas pump. When the state inspectors came by to certify the pumps each year, they pumped out 5 gallons of fuel and measured it to make sure that the pump dispensed exactly 5 gallons. They also check to see how much is left in the hose, to make sure people are not getting ripped off, and also to test the capture system that the government mandates for all modern pumps: vapors and fuel are captured and returned to the holding tank so they do not polute the environment. The amount left in the hose after pumping 5 gallons averages about 1/4 cup. So even if you only put in 1 gallon, only 1/64th of your fuel is not the right octane, not enough to make a difference.
 

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Discussion Starter · #9 ·
That makes me feel a lot better. Thanks
 

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I worked in a gas station all through high school in the 80's, and what it breaks down to is just basic science. It's a giant siphon, the tanks are buried x number of feet below ground (I believe it used to be 8ft min, I don't know what the EPA mandates now), the pumps, and hoses are above ground. When you turn on the pump, whether it be electronic via pushing a button, or the old school flip lever, you're turning on a pump that brings the fuel from the tank into the hose, and pulling the trigger opens a valve that allows the pressure from the pump to flow out and into your fuel tank. When you're done, the level of the tank below the ground draws the fuel back up the hose, then down into the tank, whats left in the hose is just a byproduct of the weak vaccum effect caused by the closed valve and the siphon.
This is one of my pet peeves in the movies... someone drives a car into gas pumps, result is a small explosion, followed by a massive one. When in fact, theres hardly enough gas above ground when the pumps aren't active to get a BBQ going.
 

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I worked in a gas station all through high school in the 80's, and what it breaks down to is just basic science. It's a giant siphon,

This is one of my pet peeves in the movies... someone drives a car into gas pumps, result is a small explosion, followed by a massive one. When in fact, theres hardly enough gas above ground when the pumps aren't active to get a BBQ going.
Ha, ha....a giant siphon.....that's a good one. :lol4:

That must be some fancy pump......that gets the gas all the way from the tank in the ground right up to the nozzle the VERY INSTANT that you pull the trigger. :roll:

So how then do you explain the security video's of actual vehicles running down a gas pump and triggering a large (although not really massive) blaze ??

Clue: Your siphon theory is a fairy tale. :eek:oops:

When the pump stops, the gas does NOT flow backwards. :bluethum:
 

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bump

Sooo, what's the verdict?

Is there nearly a gallon of "old" fuel in the line when you pull the trigger, or does the pump rapidly raplace any vapors in the line with "fresh" fuel when we pull the trigger?

This topic's been nagging at me for some time because I get more ping during the summer months.

Thanks
Kev
 

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More ping could be because the engine will run warmer in the summer months which will cause detonation with higher octane gas than in the cooler months.
 

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The internal capacity of a pipe is pi x internal radius x internal radius x length of pipe where pi = 3.142

Water capacity of pipe?
Pi (3.14159265) x D sq x L in Ft x 7.48 if inches divide by 2.31
will get you close

On average how much fuel is trapped within the gasoline pump hose ?

Here is why I ask:

On the way to the track today, after I got off the freeway (about 35 miles from home), I filled up my bike before entering the track. The problem is that I only put in about 0.9 gallons of gasoline. So I started to think, what happens if there is more than 0.9 gallons of gasoline trapped in the hose and if the person using that same hose ahead of me was pumping 87-octane gasolines, then I just pumped 0.9 gallons of 87-octane gas into the tank of my gixxer which specifies 90-min octane !!!

In this case,that wasn't much of a problem because I left home with a full tank of 109-octane race fuel, so in the worst case, I get about 104-octane average.

However, for my normal canyon runs, I use 91-octane (the highest we can get at most places in California), so if I mix 0.9 gallons of 87-octane gas with 3.6 gallons of 91 gasoline, that averages out to only 90.2-octane, barely meeting the minimum requirement. This means that I gotta plan my fueling carefully and stop doing these 1-gallon fill-ups so that I don't keep pumping 87-octane gas into my tank.

Is there anyone who would know how much fuel is trapped in the gas pump hose ?

Thanks in advance.
 

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Discussion Starter · #16 ·
Since my initial post on this topic, I've stopped taking my gixxer or my duc to the gas station for refueling.

Instead, I carry a 5-gallon container in my car. Since I feed my car 91-octane gasoline anyway, I'd just drive my car until there's about 1 or 2 gallons left, then go fill the tank of my car first (usually around 14 to 16 gallons), and then fill the 5-gallon container. And then fuel my bike from the 5-gallon container. This way, I put as-close-to-91-octane fuel in my bike. Also, for every three gallons of the 91-octane fuel I put in, I add about 1 gallon of the 109-octane race fuel so that I'd run about 95-octane on average in my duc and gixxer.

As for my SV, well, it's kinda hard to go below 87 so I just fuel it at the pump :mrgreen:
 

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Discussion Starter · #18 ·
I'm just a little anal-retentive....
 
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