Riddle me this.

[Freddy F]

Brain teaser:

A gas station in the GTA sells regular 87 octane, mid-grade 89, and premium 91.
You pull up on your bike, and you put 4 gallons of premium 91 Octane in the tank.
You pull away happy. But the reality is, you probably did not get 91 octane, you paid for 91 but got probably around 90.6.

Why?

If you prefer, you can private message me with your answer, vs. a public post.

 

[FullMotoJacket]

Pull up to a pump that was just used by BMW/Audi/Benz/etc. The liter or so that's still north of the valve in the pump + hose will be 91.

Don't know why the hell you'd want PMs over that. It's not some big need-to-know secret.

 

[GreyGhost]

Easy answer. Were you using theoretical numbers or measured values from somewhere?

 

[DownUnder]

And that my friend is why a lot of countries gas pumps look like this....



First time I saw a pump in canada I thought wtf, I'm going to get a litre or 2 of **** petrol before the good stuff comes out..

 

[Freddy F]

Don't know why the hell you'd want PMs over that. It's not some big need-to-know secret.

Easy horsey, it was meant in case someone didn't want their guess to be public, in case they thought it was dumb and didnt want others to see. See how considerate I am?

 

[Freddy F]

Pull up to a pump that was just used by BMW/Audi/Benz/etc. The liter or so that's still north of the valve in the pump + hose will be 91.

OK I'll give it to you even though what's in the hose would be 87, not 91 as you said.

 

[Freddy F]

Easy answer. Were you using theoretical numbers or measured values from somewhere?

used the volume of a hose 1" ID x 12 feet long.

 

[timtune]

How about this one ?

If a hen and a half lays an egg and a half in a week and a half, how long would it take a wooden legged monkey to kick the seeds out of a dill pickle? Stumped? The answer is half a hamburger.

Don't ask me why, ask my cousin who told me that about 50 years ago

 

[FullMotoJacket]

OK I'll give it to you even though what's in the hose would be 87, not 91 as you said.

Huh? If you use the pump right after someone in a high end car that requires premium, there will be premium in the hose. It doesn't magically go back to regular after the guy in the GT3 pulls away.

 

[DownUnder]

Huh? If you use the pump right after someone in a high end car that requires premium, there will be premium in the hose. It doesn't magically go back to regular after the guy in the GT3 pulls away.

I think he means most people in those high end cars don't know the difference and use whatever lol

 

[FullMotoJacket]

used the volume of a hose 1" ID x 12 feet long.

Not to be pedantic (ah, who am I kidding), but you're forgetting about the gas between the valve on the manifold at the lines from the 3 tanks inside of the pump to the fitting on the side of it that the hose attaches to. There's a good half liter (+/-) there.

 

[GreyGhost]

Not to be pedantic (ah, who am I kidding), but you're forgetting about the gas between the valve on the manifold at the lines from the 3 tanks inside of the pump to the fitting on the side of it that the hose attaches to. There's a good half liter (+/-) there.

And I'm pretty sure the hose isnt 1". I also think octane doesnt change linearly with percentage concentrations but I could be wrong about that one.

Edit:
It appears fuel mixing by octane is linear. Discard point two.

 

[FullMotoJacket]

I think he means most people in those high end cars don't know the difference and use whatever lol

Regardless, the previous sale is still visible on the pump. You can easily tell what gas was pumped.

 

[Freddy F]

Huh? If you use the pump right after someone in a high end car that requires premium, there will be premium in the hose. It doesn't magically go back to regular after the guy in the GT3 pulls away.

If its 91 in the hose and you fill with 91, you will get all 91.
If there's 87 in the hose, thats what you will get for the first couple seconds, then the 91 comes out. Ya with me now?

 

[TwistedKestrel]

Supposedly gas pump hoses retain 1/3 gallon of gas. Does Fuel Get Left in the Gas Pump Hose?.

Buying 4 gallons of gas in this scenario:

(1/12 * 87) + (11/12 * 91) = ~90.7

But it's not like it's hard to find stations that have dedicated nozzles for premium.

Edit: If regular is priced at 130.3, and premium at 154.1, then you were "robbed" of 30 cents

*I don't think I can emphasize strongly enough that I am saying robbed sarcastically

 

[Freddy F]

And I'm pretty sure the hose isnt 1". I also think octane doesnt change linearly with percentage concentrations but I could be wrong about that one.

1 inch I.D. That what I see all the time. It might be a wee bit smaller on the inside than 1 inch but now were splitting hairs. Why do I do this to myself?

 

[FullMotoJacket]

If its 91 in the hose and you fill with 91, you will get all 91.
If there's 87 in the hose, thats what you will get for the first couple seconds, then the 91 comes out. Ya with me now?

Wow. What part of "Pull up to a pump that was just used by BMW/Audi/Benz/etc. The liter or so that's still north of the valve in the pump + hose will be 91" in my first post didn't you understand?

 

[Freddy F]

Wow. What part of "Pull up to a pump that was just used by BMW/Audi/Benz/etc." in my first post didn't you understand?

Sorry Haven't a clue what that meant other than I would assume they all use premium, so this still makes no sense. If the last customer used regular, then you get gypped. If they used 91, then you don't.

 

[Freddy F]

Wow. What part of "Pull up to a pump that was just used by BMW/Audi/Benz/etc." in my first post didn't you understand?

Ok I think I know where the problem is. In my riddle I said you "probably" get 90.7. That because the last customer "probably" used regular., which is "probably" a safe assumption.

 

[Wingboy]

Um, what percentage of real 91 is in your tank?