single hose gas pump and 92oct dilution

[jkhawaii]

does any one know the exact about of left over fuel is allowed to mix with the next octane rating? say some one fills with 87 and than I come up to the same pump and select 92. how much 87 will be pumped before I actually get 92?
it makes even more of a differance to me because I ride a motorcycle and a fill up is only around 2.8 gallons. so if I get half a gallon of 87 thats a big difference to me.
I know there must be some kinda maximum spec and common results. I know I cant just ask the gas station attendant they only operate the cash register.

 

[obbop]

This question cries out for an algorithm!!!!!!!

 

[Master ACiD]

that fuel filler hose has a THICK layer of rubber insulation on the outside. there is also a vapour recovery line that runs parallel to the petrol expelling line. i have seen the lines disconnected from the pump when someone drives off with the nozzle still in their boot and i bet the line is about half of an american inch. so i would reason that you will get no more than a quart or so of the previous persons perferred grade before you get youre own.
this is not good for small engine owners who need premium. have a gocart, chainsw, atv or ped that needs premium? better buy it in bulk to dillute the possibly lower grade of 87.

by the way i do not believe the detergents are any different from regular to premium. actually top tier gas is required to have the same ammount of additives in all grades of gas, and id bet that non top tier gas is nearly awalys the same.

 

[mfisher1967]

That is not true. Shell advertises that they use 5X the federally required amount of additives in their 93 octane V-Power and 2X for the other grades.

 

[Greggy_D]

I have wondered about this for about 15 years. No joke. How can the station get away with charging you for 93 octane when SOME 87 is still flowing through the lines?

Granted you could reverse the situation and have 93 sitting in the line when you fill up with 87.

 

[Dr_No]

around 1L

 

[Bobert]

From what I've heard it is about a quart that you will be getting from the previous fillup. For cars and trucks this probably wont be a problem.

For smaller tanks like on motorcycles that require premium the only thing you can really do to get untainted premium gas is look for stations that have three separate hoses for each grade (getting harder to find).

 

[Craftsman]

You not only have to worry about the hose but the switching mechanism inside of the pump itself. There may be 1 to 2 litres (or about 1/2 US gallon) in the whole works...

 

[tom slick]

call your local weights and measures office, they double check all of that stuff when they do their yearly certifications on the pumps.

 

[Dave H]

Just make sure you fill up immediately after someone who has just pumped premium gas. Depending on the station, it may take a little waiting.

Dave