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[muddypaws]

When you go to a gas station that has a pump with one hose for all grades of fuel how much of the last persons gas do you get? If they buy low octain fuel and you only are buying 3 gal how much low octain do yo get?

[Blazo]

Out here in Cali, it is hard to find a pump that has more than one hose. I asked a guy that was servicing the pumps about the same thing you are wondering. He said that the amount is negligible. They have to test the pumps regularly. When they test, they sample all octanes through the same hose and don't run any gas through the hose to clear gas from previous tests. The tests do not show appreciable amounts of other octanes. In other words, the octane in your gas is not diluted or enhanced appreciably by the previous buyer.

To keep subsequent buyers happy, please make sure you always completely drain yer hose. 

[chaos901]

The majority of the pumps that do multiple grades are called "blenders" and they do it at the nozzle, not back at the pump.  The hose has two lines in it, one for Regular and another for Premium, the mid-grade is just a blend of the two. 

So if you are getting Premium and the last customer got Regular you are not pumping a hose full of the cheap stuff to get to the good stuff.

[sportygordy]

I have heard that the last gas pumped through the hose gets vacuumed back to its originating tank so you get 99% of what your paying for.

[grc]

I have heard that the last gas pumped through the hose gets vacuumed back to its originating tank so you get 99% of what your paying for.

I believe you are correct.  I guess if someone wants to test the theory they could take the gas hose and nozzle (without turning on the pump), lay them on the ground, pull the trigger, and see how much if any gas comes out of the hose.  That would be the amount that might not be the grade you want.  I think you will find it's a pretty small amount, but to be safe I would still recommend extinguishing any smoking materials.  And try to not let the station operator or employee's see what you're doing, they might get a little belligerent.  Maybe it would be best to lock the trigger open and pretend to drop the nozzle.

I think the bigger problem in some areas are the fly-by-night operators who sell mid-grade in place of premium, or el-cheapo gas from "gasoline salvage" operations in the regular tanks.  For those unfamiliar with this last item, there are companies that salvage gasoline from wrecked cars and lord knows where else, and then sell it to independent stations.  Had a big deal in the paper here last year when several people had their engines damaged by fuel from one station that was found to have bought "salvage" fuel.

Jerry

[nidan]

at the very most in worst case scenario it would only be the volume of the hose which is negligible