Anyone used premium fuel????

It is only money spent needlessly, no harm is done.

 

0 ethanol regular best mpg but it costs approx. 15 % or more and thus probably not economical. Stick with tier 1 regular from a station that turns over a lot of gas and enjoy 50 MPG

 

Incorrect, most of the time. The many components needed for higher octane that make up high test gasoline, for example, toluene, have higher combustion values than the mix for regular. In many lab tests that has been shown to be the case. Its not always true as some additives that raise octane do not necessarily have higher combustion values. Ethanol lowers both in mpg. And that mix of component chemicals will almost surely vary not only brand to brand but batch to batch for the same brand. Its the result of varying processing parameters depending on the crude feed. Refineries don't often run on one set of process conditions because the crude varies. We go to the track a lot and can assure you that 91 octane gas with no ethanol will get a slightly higher top speed on the long straights. And a couple better mpg back on the street. as far as mpg that difference of only a couple mpg means the extra cost isn't worth it for the street. There is not much difference in the injector cleaning additives, and such, either, so thinking you get better gas performance isn't all that important either. you're better off adding a bottle of non alcohol injector cleaner from WallyWorld once a month than depend on 91 octane insread of 87 octane. Besides if your gas has ethanol you have more troubles with corrosion (rust) than your gas cleanliness. And not surprising, the cleanliness of the gas stations are far more of a risk. In short, if you are going to run your Prius hard 91 octane is a good choice but not otherwise.

The reason most cars require premium is due to the compression ratio or the ignition timing. Cars that have compression ratios greater than about 8.75 : 1 need 91 octane or they will 'knock'. The limit isn't exact as the cylinder configuration and spark location and a numberof other things are involved. Many times we found cars that 'knocked' had the static igntion timing too high and resetting it back cured the problem.

 

The Atkinson cycle engine in the Prius makes expansion ratio and compression ratio (usually close to identical in Otto cycle engines) quite different. The expansion (or mechanical compression) ratio is 13 to 1, while the effective compression ratio is much lower, 8 to 1, since the intake valves do not close until the piston is about 1/3 of the way up the cylinder.

 

The only intended use for higher octane gas is to abvoid spark knock, when the gas-air mix is igniteed and expodes rather than burned. The only advantage that high test gas might have is increased heats of combustion from the components that raise the octane value.
yers ago that could be significant but not so much in the late years as the need to stretch the use ohf some components has meant lesser formulations. Such is the case for summer vs winter gas formulas and not surprised to see more than 40 different formulas based on what some eco=terrorists thinks is the proper gas for less harmful tail pipe emissions.
Routinely we fill up with premium before every trip to the track not because we think we'll get better mpg but to guard against spark knock under max accelerations. And te trip up sand back pretty well confirms that mo increase in mpg ioccurs as near as we can tell.
That said, there are places where premium is sold without ethanol and there mpg are increased; we generally do get increased mpog if we fill up at the track but that gas surely is formulated for maximum energy rather than maximum ecology. And ogf course it costs more than the worth unless you think racing is normal driving.
hope that helps. cheers.

 

My resolution for 2014 is to do some spot tests. When I fill up, sometimes I will get a sample probably just in my lawn mower can, and I will measure for ethanol% and density. And I will pay thru the nose for Premium on the rare occasion. Density should relate to energy content. Like all resolutions, don't hold your breath!

 

I tried this. I did 3 tanks of 93 octane. No results at all.

 

I only have one vehicle that requires Premium, and it's a motorcycle....but then it has 25-percent more BHP than a C-model with less than one fifth of the weight.

If you have a stock C-model?
Use regular gas, unless you have a bunch of extra money that you have nothing else to do with and let's face it....would you REALLY be driving a Prius if you had loads of extra money that you didn't have any thing else to do with?

Notice I said "stock" C-model.
I suppose that there is somebody out there that has tinkered with the C-model's motor enough for it to now require premium unleaded.
If you're one of these people the you already know whether or not you need the extra octane and why.
If you don't know?
Then you don't need it.

Good Luck!
Happy New Year!

 

Somewhere, out there in Prius land, there are some that fit that description. I know a few "financially sound" individuals that would have to "upgrade" their current vehicle to a Prius to qualify.

 

Negatory; density rarely correlares with heats of combustion For example toluene has a heat of combustion of 18k btu/lb and a specific gravity of about 0.86 while octane, either iso or normal, has a heat of combustion of about 20k and a density of about 0.7. And yes ICE's would run with much better mpg's if it ran on octane. Other components are even less which is why octanes and toluene are enhaned compounds in premium gas. There's only so much high energy compounds in crude and some crudes are much better than others.
Worse, wish I could give you a specific gravity value for gasoline so you could determine how much ethanol was contained in 'gasoline'; the way I have to do it is warming the mixture and extracting the ethanol with water and weighing the sample before and after 'washing' the gasoline sample devoid of the wash water. Even then I estimate accuracy no better than 1% because gasoline itself will absorb some water. It does clearlyshow that the gas I buy has more ethanol content in winter than summer to show why my mpg drops from 45 to 43 mpg in winter though that is compounded by the battery efficiency too.
Guess its the Sheldon is us.

 

In our area Chevron's highest octane (of 4 grades) is the only one advertised as having no ethanol. Other than that, all the higher octanes do is resist pre-ignition better, a requirement for higher compression engines, as spec'd by the manufacturers.

Still I'd be tempted to try a tank, just to see what ethanol free gas does.

 

I put in 8.9 gallons of E0 on November 27 and have only used about a gallon so far. At this rate, I won't know if this stuff is better than the ethanol equivalent until this time next year

 

....hmm let me check the density thing.
EPA report says density correlates to energy and varies about 7% MPG. That was old days before ethanol, so I do not know if 7% density variation still observed at the pump today. What I deduce from this though is: add ~7% MPG variation (due to density variation) to ethanol (3% MPG) and you have potential 10% MPG variation at the pump between a E10/Low density gaso and E0/high density gaso (such as EPA uses for MPG testing). Although EPA apparently uses E0/higher density gaso for MPG testing, I am aware EPA uses correction factors to adjust their observed MPG to real world.

Ethanol % measurement I agree you have to mix with gaso+water and measure the layers.

 

Top Tier better.....maybe, if you trust that there REALLY is what they say there is in those tanks.
I've known some tank truck drivers over the years who say you can NOT trust that at all.

As for the extra octane, that gets you exactly NOTHING in a car like the Prius.
As a matter of fact, if you buy your "premium" gas from a station that doesn't sell a lot of premium,
you might be getting really OLD gas and defeating your purpose.

The only real exception to that is if the regular gas does have ethanol and the premium does not.
In that case, the 3-4% mileage increase makes the higher price just about a wash, usually.
As a side note, I've been noticing lately the the price difference between regular and premium is going
WAY up. Used to be 20 cents a gallon; now it's more like 50 in some places.

 

It sounds so bad when I hear that on new cars.

Once major reason is that the fools are supposed run 91+ and they don't

In the case of the 87 cars they run low tier gas and have carbon issues.

All my old 87 cars never pinged even in summer due to the good fuel top tier fuel and fuel cleaners I would add from the time to time.

 

I highly recommend the non-ethanol fuel if you can get it. My C indicates not to use fuel with more than 10% Ethanol on the fuel door. I have yet to run any Ethanol in it as the local gas station near me is E0, however I am sure there will be the day, I don't have a choice.

With my previous car I did notice a reduction in my gas mileage with ethanol fuel...

 

There is NEVER any benefit from premium fuel unless the engine is tuned to be most efficient with it. It's an old wife's tale to think that all engines benefit from premium. Using it in a Prius C is like throwing $$ out the window. Users of it are ill advised. Higher octane gas does not have more energy nor does it have more "power". What it does have more of is more time for it to combust than gas having less octane. In fact, using premium in an engine that is not designed for it can actually cause a higher consumption of gas, killing MPG, and it might cause engine damage over the long run because of incomplete combustion. Octane is a regardant.

 

I agree and I don't have to be told twice. Just like the old debate of changing engine oil every three thousand miles, or less than manufacturers recommendations. Too many non high performance cars require premium fuel which is a disservice to consumers.

 

Misinformation to the public is more harmful. Why would you think that more octane for an engine would be bad. When was the last time you read in any auto manual not to use higher octane then recommended? Only lower octane then recommended can hurt an engine.

 

I agree with you Orenji in general. However, my Gen2 Prius maintenance manual (Bently) says premium can cause hard starting in a Gen2. Also I have read recently perhaps on Wikipedia regarding 3-way cat converter something like what Dan was saying: in some (older?) cars premium could overload system with more hybrodcarbons than it can handle. But I never heard Prius had this issue.

I agree there is no benenfit to higher octane. There *might* be a small MPG benefit for higher density (energy content) but of course there is no way for a consumer to know the density at the pump, except I am trying to measure it once in a while. People used to say there is probably a tend to higher density in Premium, but that may depend on EPA region etc.

Note that if Dan is correct about his theory, the reason would be that the premium could be higher density (higher energy content) so the system is getting more pounds of hydrocarbon than the air injection can handle. Which gets back to what I am trying to say, energy content could be higher in some premiums.