Initial B

iTrader: (2)

Since my car requires 91 octane, it's always nice to find a gas station that has separate hoses for each octane at the pumps. That way, you know what you're paying for should be 100% of the correct octane.

Does anyone know how much fuel volume there is from the pump handle down to wherever the manifold feeds from the 3 underground tanks (or blend valve, according to 'how stuff works') into the delivery hose? I assume that since most cars/drivers use 87 octane, I'm getting at least a liter of 87 each time I fill up from a pump without separate hoses. Just something i've always wondered....

Joeb427

iTrader: (1)

I think if there was a problem with one hose pumps,we would have heard about it over the years.

T0ked

iTrader: (2)

LOL, I've thought of this, too! But I don't have an answer...

caddyowner

This reminds me of a scene in some movie about the 50s or early 60s where kids would cruise down the main drag after all the gas stations closed and try to drain whatever remaining gas was in the hoses into their tanks.

I think there were folks during past spikes in gas prices that would fill up, turn off the pump, and then lift the hose high with the trigger open to try to get the last drop they paid for.

J.P.

this never crossed my mind as I am not worried about the .05 cents worth the 87 but here is a thread with the same concept + some math

http://www.gassavers.org/showthread.php?t=9970

InRBigness

I believe that the flow is turned off in the pump not in the handle. The pumps with the single hose get all their fuel from the top of the tank and gravity feeds it into the car.

Big Mack

iTrader: (1)

Same question was posed before...

https://www.clublexus.com/forums/the...he-pump-2.html

It's 1/3 of a gallon in a hose. I did the math in that thread, too.

Big Mack

KillaIS250

iTrader: (1)

Most people think that just because there are 3 separate hoses, that each one must be connected to a separate tank of that kind of gas. What i've come to find from doing some online research on this issue and from helping manage a gas station rebuilding project at work, that's not true.

From what I personally understand now, most pumps nowadays work something like this (and someone correct me if i'm wrong because i'm no expert by any means):

The gas pump has a series of different valves inside it designed to do different things. For most pumps these days, it seems there are usually only 2 tanks (one of 87, one of 91 for example). These 2 tanks have 2 separate lines that flow to a main line controlled by a computerized blend valve and motor pump. The middle one (89) is made by a mixture of 50% 87-Octane & 50% 91-Octane by the blend valve (it draws in 50% from each tank, creating the mixture). The valve can also make custom blends of anything (i.e. 90% and 10%, 20% and 80%, etc). There can also be a separate tank that only holds the detergents added by fuel companies, and this can also be injected into the mix separately via that separate tank and its own line. So you can have something like 45% 87, 45% 91, and 10% detergent mix depending on what the computer wants to mix.

As far as the gas that's already in the pump lines when the person before you stops filling gas, its vacuumed back up, and held in place by 2 valves that close creating a "chamber" and holding it in a place just above the tank, but before the blend valve. It's only released the next time if the pump needs to create a mixture using it, otherwise it's held there until it needs to be used again. From what I understand, the 2 valves are there because the pumps only like to push gas upwards, and don't like gas coming back down into the tanks. From what I gathered, the only time the gas should go back into the tanks underground is if the emergency shut off switch is pressed, in which case all gas in the lines is released backed into the tanks and all valves close shut after, allowing no way for it to go beyond the tank.

For pumps that have 3 separate lines on the outside, the 2 tanks feed into 3 separate lines/chambers. All controlled by different valves again. The advantage of having 3 separate pumps for each different octane only seems to be that each line has its own 2 valves creating that "chamber" holding gas in. So the 87 line already has 87 in it, the 89 line is already holding a mix of 50% 87 and 50% 91 and the 91 chamber is already holding 91. So it should make for a couple seconds quicker time to pump than having a single line.

Either way, you shouldn't be getting any 87 if your filling 91, and vice versa.

That's how i've come to understand it at least

rominl

iTrader: (4)

no matter what i think it's too little to worry about

SNiiP3R

iTrader: (3)

if there is just one hose, just wait for someone who is filling up with 91 octane or better

adamls2

LOL I was just about to say that I mean what harm could 1/3 a gallon of what ever else octane of fuel do to the car? From what I know most newer cars have something to adapt to lower octane or something (i'm not really sure just remembered something like that), but yeah, too little of a thing to worry about IMO.

gengar

Additionally, the fuel should mix somewhat when it enters the car gas tank. Even in a smaller car like the IS, a typical fillup (say, stopping at some point after the gas light comes on) will be around 13-14 gallons. So .3 of a gallon will be something like 2% of the all the gas that went in and presumably mixes, which won't decrease the effective octane by much at all.

Joeb427

iTrader: (1)

Especially with 93 octane premium in my area.

geko29

I agree that it wouldn't be an issue where a car is concerned--if 2-5% of your fuel is 87 instead of 91/93, it doesn't materially affect the octane of the mix in your tank. Where it could be an issue is for small engines. With recent smog standards for 2-cycles, they have to run very lean (read: HOT) and many newer engines in things like weedwackers, leaf blowers, and small tillers require premium fuel to avoid detonation (as well as to retain the warranty). In many cases, fuel for these engines is purchased 1 gallon at a time, and if 30-50% of it is low octane, that presumably WOULD cause an issue.

Of course, the easiest way around that is never to buy gas only for your small engines--fill up your 1 gallon jerrycan when fueling your ride. After pumping 15 gallons of 93 into my car, I can be certain that the next 1 gallon that goes into the container is also high octane.