How I lost and Increased my MPG - 2008 Prius

Discussion in 'Gen 2 Prius Fuel Economy' started by vcvtrading, Feb 10, 2012.

  1. vcvtrading

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    Hello, I am a new member, however I have been reading Prius Chat for over a year or so. After reading many post regarding fuel economy on the Gen-2 Prius, and combined with my own personal experiences, I have decided to post this comment. I own a 2008 option level two Prius. The Prius is just turning over 100k miles. We purchased it new and are the original owners. My comments are in regards to my experiences with fuel economy, and what I have done recently to improve it. The Prius is a daily driver for my wife. She commutes approx 80 miles per day in, to and from Atlanta GA. The commute is most all interstate driving (with traffic jams most of the time). When we first bought the car, we were getting 50 to 52 MPG on average. We maintained this average until we replaced the tires at about 55k miles (we were running the OEM Goodyear Integrity tires). The Toyota dealer suggested we go with Yokohama tires, so we did. Immediately we noticed a MPG decrease of about 3 to 4 miles per gallon. For the next 5k miles or so we were averaging 47 to 49 MPG. After reading a few post here on chat, I checked the air pressure in the tires and found them to be at 35 to 36 PSI. A then gauged all tires to 40 PSI. After this, we averaged 49 to 50 MPG, with an occasional 48. The increased air pressure certainly helped the MPG. This average MPG held for the next 45k miles.

    This brings me to last month, and what I did to increase the MPG even further. It was time to service the car (I change my own oil, and do my own general maintenance). I went to Autozone to buy the oil and filter. Autozone had a special on Mobile-1 (high mileage formula), and a mobile-1 filter to match. I had read some positive stories about running synthetic oil in the Prius, however I had also read negative stories (no increase in MPG as a result). With it being on sale, the synthetic oil was cheap enough for a test, so I made the purchase. I also purchased a new air-filter. I went home and completed the oil change and filters, using the synthetic. The next day I made a trip to Alabama in the Prius. My father runs a business in AL, and I frequently drive over to help him on weekends (driving the Prius). The trip is 50 miles one way (we live in GA, however not far from the AL line). When I left home, heading for AL, the Prius was showing one bar of fuel. I wanted to try and make it across the AL line before filling up with Gas b/c I wanted to try running 100% gas in the Prius. All stations in GA (that I have found) run up to 10% ethanol. AL has many places that advertise 100% gasoline. I was able to make to across the line to a station selling 100% gas. I filled up and then continued my trip. Later, after returning home I noticed my MPG averaged 55. Granted I only had about 60 or so miles on the car after the fill-up, but I was impressed. My wife then drove the car to and from work all the next week for her commute to Atlanta. After the week was up, and she was down to one bar, the MPG was holding at 52. For the last three weeks, I have taken the Prius to AL, and each time I fill the tank with 100% gas. This pattern has continued each week. I fill the tank with 100% gas in AL, and she drives all week to work, until I fill it again the following weekend. Tonight is Friday, as I write this and the Prius is showing one bar of fuel with an average of 52.2, with 504 miles logged on the tank (I have a picture that I will try and post).

    So, right now I do not know if it was the synthetic oil, or the 100% gasoline that improved the MPG - or a combination of both. In a couple of weeks, I will have to skip a weekend in AL, so I will not be able to get 100% gas. I will be forced to fill-up with the ethanol blend. I am hoping the MPG will stay in the 52 range. If so, I can contribute the MPG increase to the synthetic oil. I will update when I am able to determine.

    (I just tried to post the pic showing the MPG and 504 miles, however the system will not allow until I post at 5 messages first (why I do not know). If anyone wants to see the pic, I will be glad to email it to you. Or if member wants to post it for me, I will send, and you can post).
     
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  2. wjtracy

    wjtracy Senior Member

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    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.
     
  3. bisco

    bisco cookie crumbler

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    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.
     
  4. bshef

    bshef Member

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    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
     
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  5. uart

    uart Senior Member

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    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).
     
  6. wjtracy

    wjtracy Senior Member

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    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.
     
  7. uart

    uart Senior Member

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    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.
     
  8. seilerts

    seilerts Battery Curmudgeon

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    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.
     
  9. NortTexSalv04Prius

    NortTexSalv04Prius Active Member

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    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
     
  10. wjtracy

    wjtracy Senior Member

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    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.
     
  11. bshef

    bshef Member

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    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?
     
  12. wjtracy

    wjtracy Senior Member

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    ...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.
     
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  13. bisco

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

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    Hello folks. As promised, this is an update to my original post that started this tread. I had been running 100% gasoline (no ethanol mix) for a few weeks. My MPG was averaging 50+ consistently (sometimes 53) while running pure gas. Over the last 1000 miles or so, I have filled up with the ethanol mix, as I have not been able to find pure gasoline. My MPG has dropped to a consistent 48. Only a small difference, but enough to measure, and confirm the fact that 100% gasoline will produce overall better MPG.

    When I am able to run a consistent 1000 or so miles on 100% gasoline, I will again post an update (I predict a boost in MPG, based on the patten so far).

    BTW, I am only a few miles from turning over 100k on the Prius, and she runs like the day we bought it (new, from the dealer). God willing, we will put another 100k on her. I just watched a YouTube video of a Prius turning 400k miles. Amazing, and good to see, but I'm not surprised.
     
  15. bandit1222

    bandit1222 Junior Member

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    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.
     
  16. uart

    uart Senior Member

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    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.
     
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  17. Aristides Restituyo Jr

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    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.
     
  18. bisco

    bisco cookie crumbler

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    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?
     
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