How I lost and Increased my MPG - 2008 Prius

Thank you for the report. I also use the Mobil-1 but I am using the 0w-30 Advanced Fuel Economy...I do perceive it is helping in the winter. The Mobil-1 High Mileage my understanding from a brochure is not quite as good re: better MPG as the other Mobil-1 formulas. I presume this might be because it is a little heavier to reduce oil loss. But I won't argue with success.

 

i have read that 10% ethenol means a 10% decrease in mileage and i believe it because my mileage drops in the late fall from 65 to 58 or so and stays there all winter even if it's warm out. right now, i cannot get it over 57 and it has been 40's and 50's all week.

 

Yep..... well-known fact that Ethanol blended gas provides less energy than a tank of regular uncut gas.
In practice, ethanol is less fuel efficient than gasoline, although it offers similar power, acceleration and cruising performance.

quick search brought up this ingenious site...
http://pure-gas.org/index.jsp?stateprov=CA

 

Ethanol decreases volumetric energy content by approx 3%, so theoretically it's about 3% less fuel efficient. Most studies report around 2% to 4% reduction in fuel efficiency but some people report much larger discrepancies. I'm skeptical of the very large reported discrepancies (like 10% or more), though personally I have experienced up to 6% reduction in fuel economy with E10 from one particular petrol station in my area (even though I normally only take a 3% hit with E10).

 

If we do some quick math, ethanol C2H5OH is molecular wt 46 so that is 16/46 = 35% Oxygen. Oxygen is zero MPG in theory. Density of ethanol is 0.789 g/cc according to Wikipedia. So that density is almost same as gasoline so that means:
E10 10% vol% = 10 wt% ethanol x 35% = 3.5% oxygen in gasoline.
So for Prius 50 MPG x .035 = 1.75 MPG loss in theory.

I am not a engine combustion energy expert, but my expectation would be that 1.75 MPG is the largest possible MPG loss. There may be driving situations when you do not see the oxygen-MPG-loss (eg; when braking hard from fast speed). Also cold weather may be a time when less is more. Idling, etc.

But us Prius owners can see the MPG losses 50 vs. 51 on our screen so we hate to lose it.
49 MPG is really stinky when it could have been 50.

 

According to the following the volumetric energy density is for normal gasoline is about 34.2 MJ/L, and for E10 is 33.18 MJ/L, so about 3% less energy. Energy density - Wikipedia, the free encyclopedia

So yeah, that translates to about 1.5 MPH for most of us. And personally that's the type of small decrease I would normally see when using E10, but surprisingly the E10 from one particular petrol station here has been giving me about 6% less. I think that the thing is, those figured would be for a "typical: gas blend and probably assumes that apart from the ethanol that all other things are equal. In my case, for this particular petrol station I guess that all other things aren't equal.

 

49 -> 52 could be a combination of the switch to M1 and 100% gas. It could also be related to the grade of oil used, e.g. switching from 5w30 to 0w30.

As a precaution, check your oil level frequently. A small fraction of users report an increase in consumption after switching to synthetic, high mileage formula or no.

 

Winter blend gasoline from refiners will reduce engine performance and this is a well known and publish information. Additionally, as of 2012 the farm subsidy for corn ethanol is all but gone.Remember past Pres political elections McCain vs OBAMA. McCain did not support farm subsidy. OBAMA did supported in congress and whitehouse for Illinois farm subsidy and ethanol production. Obama would not admit that BRAZIL ethanol production is far more effective and efficient than anything the US has yet to bring to market. So this "HOW" and a little why

 

Show me the well known info.
I agree that winter gasoline has different energy content but I have not seen any data to show that this impacts MPG negatively in winter conditions. Maybe yes a small impact. But what I saw said that the winter gaso formula may vaporize better in the cylinders so this can actually improve engine MPG even though the energy content is less. Don't get me started on ethanol subsidies but as fas as I know Congress says we must use E10 ad infinitum.

 

I thought Winter blend became Year-round blend....we no longer only get "Not Quite Gas" during the winter months, we get it all year round.

Like air travel before baggage fees and TSA groupings, real gas is something only people over 30 have any real memory of?

 

...I forget exactly, because over 30, memory is the first thing to go. or is it the second thing? I can never remember.

You may be remembering about the following:
The Clean Air Act Ammendments of 1990 brought us mandated ethanol-in-gasoline from Congress. Oil industry objected strenuously, and the compromise was ethanol + MTBE. If I recall, (and I don't recall too clearly) orginally it was 10% in summer and 15% ethanol+MTBE in some areas in winter. The 15% winter requirement (ethanol + MTBE) met with many complaints (cost/smell/etc) and was rolled back to 10% year round. Later MTBE met with enviro-complaints and was replaced with all ethanol E10.

However, the above is not to be confused with vapor pressure (RVP) requirements. Winter fuel vapor pressure RVP is higher since the cold weather reduces evaporation losses. So basically in winter you are getting more butane in your winter gasoline. Butane is light, less dense, and a little less energy content, so this leads to people believing winter gasoline is less MPG. So winter gaso is a little different. However, the E10 is year round now.

 

oh great, so now i have to start another thread asking why my fuel economy is down.

 

im on my 3rd tank of non-ethanol gas, ive gone from averaging 55 to 57 mpg, to now getting 64 to 65.5 mpg. the non-ethanol is 23 cents a gallon more, bit the increased mpg is well worth it to me.

 

Wow, 16% increase in MPG for the replacement of just 10% ethanol, sounds fishy to me. There are probably other factors at work here besides the ethanol.

 

In Virginia Beach most Gas are loaded with 10% ethanol and I always managed to get 50-52mpg until recently.

For a while I’ve been hearing an increasingly annoyinghumming sound comming from my front end. After changing the transmission oil by the dealership, the noise quiet down a bit but has come back even louder. This, couple with my engines not switching as they used to, has raised my fuel consumption by @20%. It is now barely maintaining 40mph.
A friend of mine went through similar issues until his transmission locked up and he replaced it.
He owns a 2005 and I a 2008; but he claims not ever getting more than 40mpg since he owned it.

My question is, what controls the switching between engines, battery and brakes. I can see on my MFD how mainly the battery and gas engine switch back and forth and rarely from the inverter.
Any suggestions? I have also ordered another transmission to get rid of that noise and potentially getting stranded 100s of miles from home.

 

unfortunately, that is a very complicated question, and difficult to diagnose over the internet. the computers control everything.
if you don't have any trouble codes, then everything is still within operating parameters.
there are dozens of things that affect mileage, and unlikely that you have the same problem as your friend.
how many miles on her?