Better Gas Mileage Using Non-ethanal Gas?.........I Don't Think So

In theory ethanol E10 gaso has 3% less energy (3% less MPG which is like 1 or 2 MPG). But there is also variation of the energy content in the gasoline itself. Normally, in a non-reformulated gasoline region, where E0 is available, you would expect the Premium might be a little more energy. Therefore your MPG observation is a little unexpected.

We might expect the E0 Premium could range from -4% up to +10% MPG compared the E10 regular.
This presumes ethanol contributes 3% less energy, and the base gasoline can vary up to 7% in energy content.

Neither EPA nor Consumer Reports nor anyone else bothers testing MPG difference between E0 and E10 so we are stuck with rules of thumb and owner observations, which are impacted by many variables especially this time of year as cold weather sets in.

 

Too many variables to draw these conclusions. You could just as accurately say that you filled up on Thursday so Thursday is the cause for lower MPG. A thorough sampling of at least 5 tanks of each type of gas is called for, and preferably in similar driving conditions and weather.
I did just that once with my Tacoma, and found the E10 resulted in about 1 gal increased usage per fill-up. Roughly 6% lower MPG.
A moot point these days since E10 is mandated in this area.

 

my understanding was premium contained less energy, but could be wrong.

 

With the complex EPA regs, I am not sure anymore. Historically though a refinery will add more aromatics to Premium such as toluene which have more energy. Today however, especially in reformulated gasoline zones, EPA limits the aromatics content, so essentially no energy content difference between RFG grades. I would still think (from Chevron website discussion on octane) in non-RFG areas there is some tendency for Premium to have a little more energy content.

But there are many exceptions. For example, in a non-reformulated gasoline area, if you had a mid-grade E0 (say BP Silver E0) then BP, for example, would have the option to add ethanol to the mid-grade E0 as an octane-booster to make E10 Premium. If ethanol is used as an octane booster, that is one example where Premium could have less energy than a lower E0 grade.

 

Simply I would say the OP's results aren't what most would expect.

But who am I to argue with the results he is seeing?

The OP does say "The Past Few Fill-Ups" so I take it the sample size for these results is not huge.
I also take it that this gas is being purchased at one singular station. So maybe it's something specific to that station and the gas they are offering.

I'd be curious as to what would happen if you purchased gasoline in different grades at different stations.

I am far from a "gasoline" expert, so I would excuse myself from the debate, but aside from using the term "more energy" or "less energy" which I don't think is precise, my understanding has always been that higher "octane" detonates within the engine at a higher compression rate. This is suppose to create benefit in engines tuned for this outcome, and also in older vehicles reduce pinging.

In The Prius where "regular" can be used, I don't think there is significant benefit from long term use of higher octane gasoline, but that's an OPINION based on my own experience and applied philosophy. I generally run the lowest grade, at a top tier station. About once every couple of months I'll fill up with "Premium" usually before a road trip. I like to imagine that this helps clean the engine. It's probably more just a self delusional habit that I've applied to most of my vehicles that haven't required or recommended Premium. But 95%+ of my fill ups are just on regular.

Best of luck to the OP. Regardless of what anyone might tell you, I'd fill with whatever you think you are getting the best results from.

 

The last I looked, the EPA test procedure not only didn't specify octane / energy content / ethanol-oxygenate content, it didn't even measure input fuel volume at all. Instead, it measured CO, CO2, and HCx emissions at the tailpipe, and computed back to some theoretical reference (and now archaic) fuel blend. The formula expanded at least once back in the 20th Century to accommodate 'newfangled' oxygenated fuels, and may have changed since.

I agree that the E0-E10 difference ought to be swamped by other issues, including changing weather and even changes in energy density from different base seasonal blend requirements, separate from ethanol content.

I hope this is a typo, and you don't really mean E87, which is 87% Ethanol. This car is not rated for that FlexFuel stuff. You want E0 or E10 at 87 Octane.

 

A while back I posted an old (1970's) EPA reference basically saying they used energy content of the fuel as a multiplier to adjust measured MPG to a common basis, which apparently is what industry/SAE always also did in the past. I assume the technique still makes sense, but I am certainly lacking any recent references. Also EPA has in the past referred to a nominal 7% density/energy content difference in USA gaso shipments. Again I assume it still applies (in non-RFG regions) but we seem to get less open info these days.

 

All else equal (never is) the estimated difference is 3% or only about 1.5 MPG due to ethanol, or closer to as low as +1.2 MPG at 40 MPG.

 

The loss from E10 should not be 3-4 mpg, it should be just 3%, or 1.2 mpg if your base performance is about 40 mpg. At that level, it takes much better procedure to isolate the ethanol difference from other variables. And if you don't drain your tank to complete fuel starvation -- Bob Wilson was driving 120 to 130 miles beyond the last flashing fuel gauge bar in his fuel studies -- then the resulting tank mixtures will show even smaller differences.

One of the other variables is that different octane blends of E0 may well have different energy contents even before the ethanol is mixed in. When a relative was blending gasoline at a local refinery long ago (at start of career, she is now retired), she indicated that their high octane blends generally had a lower energy density than the 87 stuff, thus lower mpg. And different batches, made from different available raw bulk stocks, differed. Fuel blends and seasonal pollution requirements have changed significantly since then, so I don't know what the patterns are now.

Note also that just because a pump says E10, doesn't mean today's fuel actually has 10% ethanol. It is "up to 10%", which means it could legally be anything between 0% and 10%. While tax subsidies will encourage the full 10%, other issues or resource constraints could put the actual content lower. And a few places have been caught cheating by putting in 15-ish%, without appropriate price discounts. Without some form of verification, you don't know the actual content of your fuel purchases.

 

Yes when I did a few samples for ethanol, I found my area was closer to 10% (we are reformulated gasoline so I think 10% is mandated). I found a little lower ethanol in non-RFG areas. In my RFG area, the pump says CONTAINS 10% ETHANOL. I think they mean it.

 

I can easily imagine the RFG areas being more consistently 10% than the non-RFG E10 areas. Certain fuel characteristics are required in some places, and merely encouraged in others.