mpg with 91 vs 87, in your prius c

That's incredible low cost for Premium delta over Reg! we are much higher.

 

I'm running 93 oct from Wawa. Not sure there will be a diff in mpg.

 

WaWa? You must be in Philly/south Jersey region but you could be by me in north VA as we are starting to get some Wawa's. But most likely you are in the Northeast corridor RFG (reformulated gasoline) EPA zone, where the Premium RFG is probably not going to offer better MPG. XRAYDOUG is in Oregon where he does not have RFG, so he has a better chance for more energy content in his Premium. If you are interested I can send you a link to the RFG counties so you can see (or give us a little better fix on the WaWa location).

 

You need to learn about compression ratio and octane before you go putting "good gas"(see higher octane) in a car that absolutely doesn't need it.

The Prius C has a compression ratio of 13.4:1, so it is able to utilize lower octane than say an Audi TT compression with a compression ratio of 10.3:1 so it can handle higher octane.

When you use an inappropriate octane level for your car, you're tweaking the combustion cycle, which in layman's terms, you're making it spark before or after it should, resulting in your engine pinging, which can turn to a knock, into a thrown rod into a headache.

 

There are two or three variables, higher octane, which as far as I know does not help a Prius in most cases, as you state, but also energy content can vary. This is due to manufacturing variations, and is not guaranteed to be higher in Premium, but might be depending on where you live. Another variable is ethanol content, most of us are E10 but some E0 out there. Generally speaking it will not be economical nor desirable for a Prius owner to pay more for higher octane grades or E0, but some folks are trying to maximize MPG and/or cruising range. A few Prii drivers feel they may have a special case where they are seeing better MPG with Premium and the cost is not too much more, so they feel may break even or pay off...but this rare at the moment in the U.S. market (as regulated by Congress/EPA)..

 

That's probably what it is: higher octane gas is burning slower, so you probably have more energy wasted on heating. Normally that would mean less MPG, but since it is in-town and it goes EV faster, you get reverse effect. I'd bet if it were on long trip you'd see savings switching back to 87.

Irregardless you are not saving money using higher octane gas.

 

With the reformulated gasoline in the Northeast (east MD, NOVA, east PA, NJ, east NY etc etc) there is essentially no benefit for Premium as all grades can be thought of as equal by EPA mandate and E10. Once you get to OR or (out past Hagerstown) other non-EPA-RFG states there can be more variations. Usually it will not pay off, but you might get better MPG. Problem is MPG (energy content) is not a spec so it varies and there is no way to generalize except to get data (I get a sample in a gaso can and measure weight, but that's useless data here in NoVA it always weighs the same).

 

I would have to dig out our receipts from west coast trip to see if there were any anomalies with gas in OR.

OR is the only state in CONUS which does not allow to pump your own gas. There was a NJ, but well it is no more.

Problem I see is that "C" tank is very sensitive for many pumps and can cause premature shut off. Also pumps dispose by volume, so depending temps, adjustment etc you get different amount pumped. This would not matter if he goes by trip computer MPG.

Another issue with many locations in west that with cheap E85 around there is too much discrepancy in alcohol content, esp when gas was $4. And they sell 85 and 86 regular also. At many locations 85 would be more expensive than 87, and E85 has been much cheaper. So 87 would be a mid-grade for them, and they would make it by mixing more expensive 85 with E85.

Unfortunately they do not store it premixed, it is done during dispense. And the cheapest way for the gas station owner to make free money by adjusting the ratio to ~20% or more content.

 

In general what you might notice is reformulated gasoline (our stuff) is lower energy content because that's how EPA achieves the cleaner burning formula. Of course the ethanol is also lower energy content. NJ still same as OR right? (does not allow self serve). I don't know if you are following some of the fill-up threads but some of us are turning the nozzle 90 degrees to help get fuller fill-ups. I am doing this but usually my wife fills up so I don't have too much data on it yet.

 

I'll try it next time. Wed was my first "C" fill up, and the pump would shut off every few seconds, unless kept really low. The same pump didn't give any trouble on Gen3 or any other cars. I will try different pump and 90deg trick next time.

 

Close but no cigar.
It is mixed when it goes into the tanker trucks that deliver the fuel to the station, or at the terminal right before the trucks fill.

The station owners have NO control of the ratios.

 

I assumed Cyclo was talking about special blender pumps. Blender pumps allow the consumer to dial in 15% ethanol which several car manufactures have appoved and US EPA has approved. Blender pumps if widely available would allow consumers to choose 15% ethanol, but the issue is cost and availability of the special pumps. I've never seen a blender pump.

Currently the ethanol lobby wants to go to E15 (15% ethanol) but due to the E10 (10% "blend wall") that 15% goal is currently stymied. The 10% blend wall is caused by a couple things: some cars not approved for 15% but more to the point the whole E10 blending/distribution system has corrosion/issues over 10% ethanol. So the blender pumps provide a way in theory to break the 10% ethanol barrier to help meet Congress's ambitious ethanol quotas which currrently exceed the 10% blend wall level.

 

If you go to gas stations which sell mid-grade gas (89 around here) it is made by mixing regular (87) and Premium (93) in the pump. Mid-grade gas is a scum, it does not exists in nature.

All additives (detergent, octane booster, alcohol, etc) are added to gas at the terminal when it is poured into tanker truck. Gas companies share terminals, so when you are buying gas at Shell station it could be Texaco or Exxon/Mobil gas, but the additive package is unique to the gas company.

The pumps are checked and sealed by state department of weights and measures, but unfortunately there are ways around it.

There is a lot of shady business going on: the software on gas stations had been hacked and it is not really protected by any safeguards. Another illegal profit venue is to bring gas out of state. Sell it and pocket the tax difference.

BUT you are correct, the easiest way to adjust alcohol ratio at unload.. dump some E85 from the tanker into regular tank at gas station.

 

hmm...I checked ethanol% twice last summer...both times it was 9% or less.
Messy mix with water, don't try it unless you need to and have better equipment than I did.

 

E85 is expensive in Mid-Atlantic, it makes no sense to mix it in.

Mid-West different matter. It was an issue every time I've been through South Dakota. In fuelflex car it just meant really bad MPG, but on the bike w/o oxygen sensor I had to pull off the highway due to overheating. No issues after switching to more expensive 86 regular.

 

Well I guess that gives us another possible reason why folks like XrayDoug see better MPG with Premium. If the Regular is >10% ethanol that's another variable. If it was me in I would be occasionally measuring density, ethanol, and fuel temperature to see if there is a difference. But here in NoVA it makes no sense to check for variations as we no variations (reformulated gasoline).

 

But that has no bearing on the ethanol content or when THAT gets blended.
AND not all areas or station brands do it that way.
Some actually have 3 tanks in the ground.