I have a 2007 Prius. It has a digital MPG gauge which shows both real time consumption and average MPG. After filling the 12 gal.tank, I can monitor consumption immediately. I have noticed great fluctuations in MPG, depending on where I buy gas. Even Chevron, my choice, goes up and down. My best average, which I attribute to “GOOD GASOLINE” has been 51.6. But, after certain tankfulls it drops to as low as 43+. It isn’t my imagination. Everyone tells me that octane (87 in this case) should always be the same, and that it is “regulated” and “monitored” by the Government. My question is WHY??? Why should there be such a difference in the same octane rating, even when buying from the same station: one time good; next time worse. WHY??? Is it possible that the stations are cheating? It is the SAME car, SAME driver, SAME small town (Hopkinsville, Kentucky–about one hour from Nashville). I would appreciate hearing a discussion of this on the air. Please inform me about when it will be on. I suppose many other drivers with digital MPG gauges have discovered the same thing.
Stanley Crabb (RevStan for short)
Gasolines do vary season to season, but it’s surprising to have this big a variation.
There may be slight differences in gas seasonally, but your driving style, and on board computer will be the cause of most of the differences.
We always advise that driving moderately, and shopping for the lowest pump price will save you the most money in the long run.
My guess is there is no real difference in the fuel you are getting. Most all stations in an area get their fuel from a single source. They may or may not mix a little different additive package, but that is not likely to change the mileage much if any.
I would suspect other issues, like more or less highway driving, or more short trips etc. It is also possible that you are not filling the tank the same each time.
A significant variable is whether ethanol has been mixed in. Around here (MN, WI) most gas has 10% ethanol, according to labels at the pumps. Some stations claim to sell pure gasoline, no ethanol. I usually buy whatever’s available conveniently, but I do have about a 5-10% MPG reduction when using the 10% ethanol mix. My 1999 Plymouth Voyager can use E85 - 85% ethanol, 15% gasoline - and with that its MPG is very much reduced, 20% or more. My owners manual also specifies a special oil to be used when using E85, to avoid engine damage. Once I read that, after using about 6 fills of E85, I stopped experimenting with it.
What do newer cars’ manuals say about E85, as far as the specs for the motor oil to be used?
It looks as though monitoring mpg feature of your car is working, but just for kicks, I’d figure it
manually every once and a while to make sure it is accurate. Fill up the tank, write down the mileage,
when you fill back up, write the mileage and gallons down and divide the mileage by the gallons.
Do this every time you fill up. (I keep a notebook)
What is going on with your mpg (miles per gallon) is you’re running gas with ethanol in it (gasohol)
and the “good gas” (Gasoline.) Its not the octane, it’s the ethanol. Your car and most others
are designed to run on GASOLINE. On your car’s exhaust system is an 02 (oxygen sensor) which
measures exhausts… HOWEVER, it does not recognize alcohol exhausts, only hydrocarbon exhausts.
So when you’re running the 10% gasohol/ethanol “blended” fuels the 02 sensor sees an engine running 10% lean. Now the 02 sensor contacts the computer and tells it about the problem… To correct the problem the computer tells the injectors to open up 10% - 11% more to compensate for the loss. NOW, your car is running rich, or in the old days terms, flooded. The alcohol burns, your car just doesn’t know it. So now that you know why, lets explore the costs of using ethanol.
To do so you have to know: 1. YOUR mpg with ethanol
2. YOUR mpg with gasoline
3. the size of your gas tank
Lets take for instance my car.. I get 16 mpg with gasohol and 20 mpg with gasoline...a difference of 4.
My tank is 20 a standard 20 gallon. That means I can go 80 miles further with gasoline. How many gallons does that relate to? 80 miles divided by 20 mpg… equals 4 gallons. Whats the savings I get from buying
gasoline? $4.00 a gallon times 4 equals $16.00 dollars saved per 20 gallon tank. Per gallon it comes out to about 66 cents a gallon. Most people who are not keeping up with their mpg only realize that they are saving 2 or 3 cents a gallon at the pump but wasting 66 cents on the road.
I think for your car, since its obvious you’ve been running gasohol in your car, I’d consider changing the fuel filter and only using gasoline products. Currently, the major brands are quietly changing to gasohol and not putting any stickers on the pumps… so it is up to you to ask the mgr what they’re selling and keeping up with you MPG to make sure.
Hope this helps you understand whats going on inside your motor and how much it’s been costing you.
Rick
Some stations claim to sell pure gasoline, no ethanol.
Your stations have a choice. I thought that was mandated by the EPA. Every station here in NH/MA and NY that I’ve ever used has 10% Ethanol.
As far as are gas stations different. There seems to be a difference to my vehicles. They may get the gas from the same storage tanks, but the additives are different. I notice a big difference when I fill up with Mobil/Exxon. Gas mileage drops and less performance. I get the BEST performance from Hess and Gulf.
Caballero, are you saying that 10% ethanol mix is reducing your mileage by 20%? That’s hard to believe, since it is a MUCH larger decrease than most see. I’d get my car checked out if that was happening.
BTW, most states now mandate 10% ethanol blends, so you have no choice. It’s not the oil companies sneaking it in. They just don’t want to have different blends all over the place.
The “MPG gauge” in your car has little to do with the actual fuel consumption in your vehicle. It’s a computerized “guess” as to what the mileage might be. The brand and type of gasoline you choose will make little if any difference. Turn your A/C and headlights on and off and watch your gauge dance around.
If you want to check your mileage, figure it out on paper by dividing miles traveled by gallons used. It will be somewhat less than what the gauge is posting, for sure…
Not usually a guess these days - electronic fuel injection lets them calculate exactly how much gas is being used, tie in the (electronic) odometer, and you can get very accurate #s.
I haven’t seen the advertisements about one brand of gasoline producing better mileage than another brand. Years ago, Shell had TCP and later had platformate. D-X had boron. Mobil was M2PG or something like that. In the cars that I had in those days, the mileage seemed about the same no matter what I put in the tank. I doubt that things have changed much since that period of time.
Years ago, Consumer Reports used to determine the gas mileage on a car by hooking a container to the carburetor (I told you this goes back a ways) that contained a precise amount of gasoline and determined the mileage under carefully controlled conditions. There are too many variables besides the gasoline that influence the gasoline mileage. I just returned from a trip in our 2003 Toyota 4Runner. Going to our destination, I averaged 26.5 by the digital MPG. The return trip yielded 23.9 I drove the same speed in both directions. I would guess that gasoline brands are more alike today than they were 45 years ago and I couldn’t tell much difference then. I think back then that Sunoco added a blue dye to their gasoline which probably made absolutely no difference in the mileage. I do remember back that we were on a tight budget and I bought my gasoline at an independent station because the price was lower and I got a free drinking glass for each fill up of 8 gallons or more and we needed the glasses.
Running the A/C and or defrost could have the drop in gas mileage that you have described. Take note of how the HVAC is being used.
The weather was about the same in both directions and the 4Runner has automatic temperature control which we keep set at 74 degrees. However, the difference, I believe, was due to some other variable than the gasoline. The only thing I can think of that made the difference was that before I left home on Monday, I had skimmed milk on my Cheerios. This morning, I could only get 2% milk for my Cheerios. Maybe my additional weight made the difference.
The point is that it is hard to duplicate the same environmental conditions and same driver performance. I don’t worry about differences of plus/minus 3 miles per gallon.
More ethanol means much less fuel mileage which means much greater tax revenue for states. There are many dimensions to this topic and many are political. More ethanol means higher crop prices for farmers, as well.
Silverqc1,
If the mileage drops 20% so be it. I don’t argue with numbers that match all three of my cars results.
I did know a person living in Huntsville… driving to work in Hanceville. Its about a 60 or 70 mile one way trip. He was driving a small SUV. Got lousy MPG so I told him about the difference as I just told you all. He took it one step further and tested 2 tanks each of different brands of gasoline.
He was getting 20 mpg with ethanol
24 mpg with Chevron
24 mpg with Shell
26 mpg with Texico
I’ve e-mailed Shell Oil about ethanol and they can’t tell the Shell stations what to sell since most are independently owned.
If there is a label on the pumps stating in some form or fashion “NO ALCOHOL in our gas”… then by federal law, only gasoline can be sold thru/from the pumps. HOWEVER, if there is NO
STICKER.(and MOST do not have stickers)…its anything goes and sometimes the station don’t know it because the distributors of different brands help each other out when one or the other runs low and a customer needs their underground tanks filled. Thats why it is up to each of us to keep up with our own mpg.
I’ve never recommended to some one using gasoline to find out how much money they’d be wasting if they switched to GASOHOL but I have saved friends and family hundreds of dollars by convincing, (and quite
easily) the benefits of running GASOLINE.
I know one of the selling points of ethanol is that it is “suppose” to mix with water in the tanks and clean your system…but what happens when the alcohol breaks down?..it goes back to water. HELLO?
I hope this encourages anyone using ethanol to test their mpg and switch to gasoline. I think ethanol is a scam and it is indirectly causing the gas shortage resulting in higher prices.