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Discussion Starter #1
This is too weird.

Normally I use Chevron Regular grade from the corner gas station. Mileage runs 39 to 44 mpg, with 44 being the norm.

This morning I noticed the Shell station was 10 cents lower on their sign (Chevron was $3.19, Shell was $3.09 - both regular grades).

So I decide to treat the car to some Premium grade with their V-Power additive since the Shell Premium was only 10 cents higher than the Chevron regular grade (Shell V-Power was $3.29).

While puttering about this morning on my normal route, I finally glanced at the Consumption screen and it was showing anywhere from 56-60.x mpg!!! Leveled out at around 57-58 mpg. The 60.x number kinda struck me hard as I've never seen the thing read that high other than the coast 99.9 number. Never seemed to settle in the mid-to-upper 50's either.

Anyone ever try using higher octane or switching brands to see if their mpg numbers change? I dunno, but a 13 mpg gain seems pretty significant for a brand and octane shift.
 

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Talk to us when you finish the tank. Your car was already warmed up when you filled thus avoiding the first 5 minute warm-up penalty. You don't mention how far or how many minutes you drove...also a major factor.

I often arrive home after filling up showing 70+mpg on my MFD..but by the time I get to work the next morning it's down to ~60 or so and by the end of the tank I'm right where I usually end up.

BTW, you're not 'treating' you car to anything by using premium and you may begin to notice pinging. Premium offers you no benefit and has potential harm and the high cost only pads the oil companies already bulging wallets while flattening yours.

Sorry to burst your bubble.
 

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Do you have a classic prius, or HSV? Either way, I also have to agree...wait until you finish the whole tank and then tell me if you see any significant mileage difference. Premium gas wastes your money unless your car is already old and specifically designed to use it as dictated in the owners manual (The Prius owners manual recommends 87). It made a difference, for instance, in my old 1985 Ford Tempo, there was significantly less knocking when filling up with premium. Ditto for an old 1982 Dodge pickup I drove a few times. But not the Prius.
 

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efusco said:
Talk to us when you finish the tank. Your car was already warmed up when you filled thus avoiding the first 5 minute warm-up penalty. You don't mention how far or how many minutes you drove...also a major factor.

I often arrive home after filling up showing 70+mpg on my MFD..but by the time I get to work the next morning it's down to ~60 or so and by the end of the tank I'm right where I usually end up.

BTW, you're not 'treating' you car to anything by using premium and you may begin to notice pinging. Premium offers you no benefit and has potential harm and the high cost only pads the oil companies already bulging wallets while flattening yours.

Sorry to burst your bubble.
I agree. I just filled up with 87 for the second time after burning 89 grade twice. Each was a half-tank fill, an I hand calcualted the mpg each time. All other conditions normal, even the same service station. On mu first 1/2 tank, I lost 10% (average 55.47 down to 50.5). On the second 89 octane 1/2 tank, it dropped down t 45.99. I filled up (1/2 tank again) with 87 and returned 47.74mpg. Again, all conditions the same. I filled up today (another 1/2 tank of 87 octane); we shall see what it does.
 

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i was told by my service tech not to fill up with premium because it could actually cause problems ie: no starts and rough starts. I havent ever done it but who knows?!
 

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Discussion Starter #6
I don't know what is going on, but I just took it out again on shopping errands and the thing never dropped below 52 mpg!?!

Fwiw, the early morning commute to work just about fills the display, around 25-30 minutes in length (maybe 20 miles in town).

Still, it is very odd the Shell gas (never used the new V-Power stuff before, even in my bikes since I live close to a Chevron station) changed something. For all previous tanks (Chevron) it seems to start around 38 and then finish at 44 for me on a tank. This Shell stuff starting out at 56 is just odd to say the least. The only thing I recall at the pump was the ad that says the Shell V-Power has 5 or 10 times the detergent properities that is minimally needed by the EPA.

...and no, I do not have any vested interest in any oil company!

If this holds true, I know a station that has some 104-106 octane racing fuel I may need to try out. Fwiw, I did try some of that stuff in the motorcycle some years ago. All I detected (wasn't measuring mileage numbers) was a far smoother idle as the antenna didn't even wiggle.
 

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Higher octane will lower your mileage. The anti-knock compounds take the place of gasoline in that gallon you burn, so the energy content is lower.
 

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You might have done just as well using 87 grade of Shell. In order to qualify for Top Tier, ALL grades have to have qualifying detergents. Since both Chevron and Shell are both Top Tier rated, any octane would qualify. The Chevron might have more detergent, therefore less energy producing gasoline.
 

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Shell gas

No Chevron where I live, but so far Shell gas gives me noticably better mpg than other brands. And I have tried all three grades!

I see no degradation with premiums, as I expected to happen. All seem better than regular from Exxon or Mobil, my next tier grades I've used.

I used V power one tank, because I had a coupon for it. I used the mid grade because they ran out of regular.

Normally I use regular.

I did buy an inferior gas of another brand which was supposed to be 87 octane and got terrible mpg. It got better when I added some ocatane improver but not up to normal.

Between Shell and that bad gas brand I've seen a spread of about 8 mpg with similar driving over whole tanks.

Shell to Exxon or Mobil seems to be about 1-2 mpg different.
 

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I haven't read this whole thread, but I wonder if you're doing your tests only one tank at a time, or for more than one tank at a time.

The reason I mention this is that I often get wild fluctuations of mileage from tank to tank even when I do drive consistently the same. But over the course of 2 or 3 tanks or more, it usually equalizes out.

I suggest you do each of your measurements with 3 or 4 consecutive tanks for each brand/mix of fuel, so as to eliminate odd fluctuations and discrepancies in measurements.
 

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I never pay attention to tanks. I go by the mfd readouts over controlled test loops. This is repeatable right down to about 1 mpg. Tankfuls vary all over due to changes in ac usage etc.

My test loop is about 30 miles with repeatable speeds for each section and minimal traffic lights.
 

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The other way to see the effect of bad fuel is to just measure at one speed at a known point on a level highway. It is obvious within a couple of minutes if you have bad fuel. Like with good fuel I run 55 mpg or better at 65 mph on level at 70-80 degrees.

With some of the bad fuel I've been unable to ever get over 49 mpg!

You do have to do this at the same temps or make corrections for that.
And of course do it post full warm up, and battery charge at normal set pt, and AC turned off.

Course it heps we have little wind here.
 

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KTPhil said:
Higher octane will lower your mileage. The anti-knock compounds take the place of gasoline in that gallon you burn, so the energy content is lower.
There are no 'anti-knock' components in higher octane gasoline! Higher octane is simply more resistant to compression detonation. This means at higher compression ratios (typically found in higher performance cars) it won't detonate early before the spark.

If anything, the *potential* energy is higher because it can be mixed with air at a greater density.
 

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sigh... i will say this and only this.

DO NOT use 100+ octane in your car. even using premium is not a good idea. it specifically states to use 87 octane in the owner's manual. toyota tech hybrid training states that anything over 7 may cause starting problems.

octane rating is a number. it has to do with engine conditions. you're using gas your car was not made to use.

that is all.
 

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In the US, octane rating is the given by (R+M)/2. The owner's manual states to use 87 octane.

There are several reports of Prius run on "premium" high-octane fuel. The result? Check engine lights with an engine misfire code.

In the US, all gasoline sold has to have additives to lower emissions. Different companies use different additives, but the additives all do the same thing. The additives are added prior to truck delivery of the fuel to your gas station. (The fuel can be from any oil producer - it all gets mixed in the pipelines...) However, the posted octane on the pump is the minimum octane rating that can be dispensed from that pump. A station could sell the exact same high-octane gasoline in all pumps if they want to.

Higher octane gasoline actually has less BTUs than a lower octane gasoline. So, unless you have a car that is built for the higher octane or can adjust for it (the Prius isn't one), you will get lower MPG by using the higher octane gasoline. (A car that requires the higher octane fuel will usually get better MPG when given it.)

and it looks like it's time to quote http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm again...
Federal Trade Commission Facts for Consumers:
The Low-Down on High Octane Gasoline
Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.

What are octane ratings?
Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

What's the right octane level for your car?
Check your owner's manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.

Will higher octane gasoline clean your engine better?
As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

Should you ever switch to a higher octane gasoline?
A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Is knocking harmful?
Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.

Is all "premium" or "regular" gasoline the same?
The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

For More Information
If you're concerned about the accuracy of an octane label - or if you don't see a yellow octane sticker on a gasoline pump, write: Consumer Response Center, Federal Trade Commission, Washington, DC 20580.

The FTC works for the consumer to prevent fraudulent, deceptive and unfair business practices in the marketplace and to provide information to help consumers spot, stop and avoid them. To file a complaint or to get free information on consumer issues, visit http://www.ftc.gov or call toll-free, 1-877-FTC-HELP (1-877-382-4357); TTY: 1-866-653-4261. The FTC enters Internet, telemarketing, identity theft and other fraud-related complaints into Consumer Sentinel, a secure, online database available to hundreds of civil and criminal law enforcement agencies in the U.S. and abroad.

October 2003
 

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It's the Weather...

Your increase in mpg may just be the change in weather. Our 2002 classic Prius usually gets about 44-46 mpg around town in the summer with the AC running much of the time due to the 105-110 daytime highs and 90-100 early evening lows.

Earlier this month, the overnight lows dipped into the mid-70s and I was able to shut the AC off for a couple of weeks. Our mpg shot up to 51-53 mpg, with one week at 56.5 (a record high for our Prius).

I suspect that even with the AC running off of the battery on the newer models, a weather change could noticeably affect others' fuel economy (at least until the ICE has to run longer to heat the passenger compartment).

Also, as you may have read frequently on this forum, driving habits greatly affect fuel economy. I thought that after driving our Prius for several years over the same route to and from work, my habits and mpg were pretty stable. However, when gas prices peaked a few weeks ago, I exaggerated the pulse method I have used for years, which resulted in the record high, above. This is about 3 mpg greater than I had previously achieved driving the same route.
 

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My MPG is definitely better with Shell Premium in all of my cars. It's the best gasoline of any major brand in terms of fuel economy that I have used. It's better than Chevron (in my fuel economy tests over 2 years). I've been switching between Shell and Chevron over that past 2 years and have consistently seen better MPG with Shell.

Both of my Lexus vehicles get better MPG with premium gasoline (one requires premium, the other does not). My 25 mile (each way) commute is my real-world test scenario. There are only a few traffic lights and my driving patterns are the same each day. I use the instant MPG readout of my vehicles, and I reset the AVG MPG at every fill-up. I even calculate MPG manually as a backup.

If you buy premium, don't buy Unical/Union 76 or you could have the starting issues mentioned by someone already. This happened to me when I filled up my GS400 with 76 Premium. I had my car towed to the dealer because it wouldn't start. The situation was this: I started my car to back it out of the garage and turned off the engine. A few minutes later the car wouldn't start, so I had it towed to my dealer. They just let it sit for a few hours and tried it again, the car started up. The dealer sees that problem somewhat regularly, they said to use Shell Premium or Chevron Premium if you are so inclined to use premium, and certainly not to use 76 premium. 76 uses a different technique to boost the octane. For me, I now use Shell almost exclusively. When I do use other brands, I notice a decrease in MPG, but when I use Shell Premium I get better MPG results. This I have experienced over 2 years time. I have never experienced a starting problem with Shell Premium or Chevron Premium.
 

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A Prius is designed to run on regular (87 octane, 85 at Denver elevations). Using premium is a waste of money and lowers mileage. There were also some reported instances of the 2001-03 version of the Prius having fuel injector problems with exclusive use of premium. Haven't heard of this for the 2004+ though.
 
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