Here’s a question that I don’t think that I have heard on the show or read in this forum but I think Kick and Klack would have enjoyed discussing. (Klick and the late Klack? Klack and the late Klick? Do we know who is who?)
How much gasoline is left in the hose at the pump between fill-ups?
I drive a 2005 Mini Cooper S. Specs say I should use 91 octane. There is only one hose at the pump from which 87, 89, 91 and 93 octane gasoline is dispensed. When I select 91 octane and start to pump, how much 87 octane am I putting into my car before I start getting the good stuff if the last person that used the pump had selected 87 for his car? Of course, the next person using the pump after me will be getting a bonus of 91 octane for that same quantity when they select their lower octane gasoline.
I think that maybe I should sit and wait until I see another vehicle that uses premium and follow that driver to the pump make sure I am getting my money’s worth!
I think that maybe I should sit and wait until I see another vehicle that uses premium and follow that driver to the pump make sure I am getting my money's worth!
This is an interesting question that I’ve never considered. I’d guess the amount left is under a gallon. If you’re filling up when the car is past half empty, the overall octane is probably within an allowable tolerance. I don’t know if there are motorcycles that take premium, but maybe this is a real issue for them.
Instead of waiting for another vehicle, you could just add one gallon of 93-octane to counteract whatever’s in the hose, then fill up with your 91-octane as usual. That would be quicker.
By the way, I think PvtPublic was joking with you, in case it didn’t come across that way.
I think that maybe I should sit and wait until I see another vehicle that uses premium and follow that driver to the pump make sure I am getting my money’s worth!
If it were me, I really wouldn’t worry too much over the 20-30 cents you might be losing in the worst case scenario.
Not all gasoline hoses have the vapor recovery system. My state (FL) doesn’t have them. My home state, does, but only in certain counties.
Given that, the amount is @missileman 's 0.4 gallons to about half that at 0.2. For an 8 gallon Mini fill up, that is 2.5 to 5% max of 87 octane (worst case) mixed with 91. It is only 4 octane points so you are buying maybe a 90.8 Octane fuel mix. Octane numbers are minimums and probably not accurate to even a single decimal point, so 90.8 rounds to 91.
If you are THAT worried about spark knock, buy 93 Octane and sleep well!
AND…unless you’re pumping a mere gallon or less ( chain saw, weed eater, snowblower ) the dillution ratio into a tank full will be un-calculatable…stop wondering.
It used to be years ago the shutoff valve was inside the pump, not at the nozzle. Did any of you ever do what teenage-me … well … might have done … on occasions when funds were low and you just needed a little more gas to make it to the local hamburger shop? Pull into a gas station after it was closed, and empty any gasoline left in the hoses into your car’s gas tank? … lol …
I tried Googling for a standard inside diameter, and was unable to find any. I’m sure there must be one. I worked for a company many years ago that made potable water and fuel tanks and the pumping systems for military tank trucks, but cannot even remember our pumping system vendor’s name. Our specialty was the tanks.
I don’t even remember the number of the chassis we mounted them on. They were “offroad”, had four driven axles, all four front wheels steered, and it could ascend a 60% grade. It had a cabover setup with a lower front end tapered highly to accommodate a rapid transition. That’s all I remember. It was a long time ago.
Those hoses are pretty thick, the inside diameter is maybe 5/8" …So the amount of gas in the hose is maybe a quart…The octane difference is insignificant…But if you are obsessed about it, bring a one gallon portable gas can with you and fill it first. Burn it in your lawn mower or your other car…
My unscientific guess as to the remaining amount in the hose and based on working in a gas station with one iffy pump that had a tendency to pool in the hose more than others I’d say half a quart maximum.
Even if the hose held a full gallon of 87 octane it’s not going to make any difference in the performance of your car.
I hesitate to jump in on as silly a question as this, but can’t be more than a few ounces left in the hose. Trying to get my Pontiac started one winter morning at school, I needed to prime the carb so we walked to a station down the block. We had no gas can or anything but with several pumps were able to get a soda can full out of the hose. Lost a good rain coat in that effort but that’s another story.
