Why is my Prius using so much gas even I'm in Eco mode all the time?

wing200p

Hi















I just bought a Prius II 2010 5 days ago. It has 125 miles on it already and after 5 days driving it has















360 miles that means I drove 235 miles in 5 days. The dealer filled up a full tank of gas for me before I bought it. It had 555 gas miles left and I checked today it has 240 left means I used 315 gas miles.















This is kind of confusing. I only drove 235 miles in 5 days but how come it says I used 315 gas miles?















And I use Eco mode almost 99% of the time and I barely accelerate even on the high way. Hope you can understand my questions.

JerryJ

1. Tire pressure. The 35/33 that is on the vehicle placard is only valid if the assumptions made are actually in line with your conditions. Typical assumptions for family sedans are:































A. Ambient temperature of 65F. If it's hotter or colder the pressures need to be increased.































B. Maximum sustained speed of 65 mph. For higher speeds increase by 3-4 psi.































C. Load is as the engineers envisioned the car being normally driven. This may not be GVW.































D. A pressure check before every driving day. If you don't check your pressures daily, you need to add pressure so that it never falls below the minimum 35/33.































Many Prius drivers (including me) run the OE tires at 44/42. There isn't any difference in ride and the mpg is much better.































2. Ambient temperature. Cold weather reduces mpg in all cars by 25% or more depending upon how cold. There are several reasons: Winter gas, denser air, longer warm up times, use of cabin heat. The difference with the Prius is that you can't help but know this is happening because of the display. Most cars don't tell you so unless you keep a logbook you'll never know. There are things you can do to increase the mpg in cold weather: Use a block heater, block the lower grill, don't set the climate control higher than 70, always use auto.































3. New car. My Prius increased by one mpg every month for the first eight months.































DATE__________ODO____INC_____AVG















11/10/03______342____342____44.7 (5.3)















11/22/03______666____323____45.1 (5.2)















11/24/03_____1037____370____46.3 (5.1)















12/08/03_____1424____387____47.9 (4.9)















12/19/03_____1836____411____48.0 (4.9)















12/29/03_____2248____412____50.4 (4.7)















01/09/04_____2668____419____48.3 (4.9)















01/23/04_____3080____411____48.4 (4.9)















02/01/04_____3376____295____48.2 (4.9)















--- Trip to NE -20F blowing and drifting snow.















02/02/04_____3588____212____39.9 (5.9)















02/02/04_____3872____283____39.7 (5.9)















02/05/04_____4162____290____39.2 (6.0)















02/08/04_____4413____250____37.8 (6.2)















02/08/04_____4698____285____38.1 (6.1)















02/13/04_____5089____390____44.6 (5.3)















--- End Trip to NE















02/25/04_____5528____438____49.7 (4.7)















03/10/04_____6013____485____51.8 (4.5)















03/23/04_____6435____421____49.8 (4.7)















04/05/04_____6898____463____52.2 (4.5)















04/16/04_____7370____480____51.7 (4.5)















04/28/04_____7863____483____53.3 (4.4)















05/11/04_____8352____488____51.7 (4.5)















05/25/04_____8865____512____50.1 (4.7)















-- High temperatures start here















06/09/04_____9363____498____51.4 (4.6)















06/20/04_____9857____498____50.7 (4.6)















07/03/04____10341____484____51.3 (4.6)















07/17/04____10890____547____52.3 (4.5)















08/02/04____11392____501____52.0 (4.5)















08/14/04____11891____498____52.6 (4.5)















-- High temperatures end here















09/02/04____12404____513____54.8 (4.3)















09/15/04____12889____484____52.8 (4.5)















09/25/04____13350____460____53.3 (4.4)















10/06/04____13857____507____55.5 (4.2)















10/21/04____14363____505____54.9 (4.3)















11/02/04____14841____478____56.2 (4.2)















11/13/04____15149____308____55.2 (4.3)































2004 Prius MPG from the logbook. (Complete years only):















2003-2004 -- 50.8 mpg 17,628 miles















2005 -- 52.6 mpg 14,688 miles















2006 -- 56.3 mpg 16174 miles















2007 -- 57.3 mpg 18384 miles















2008 -- 59.9 mpg 21755 miles















2009 -- 61.4 mpg 16177 miles















2010 -- 65.2 mpg 12134 miles































5. Using the battery too much. The secret of the Prius is that it gets its good mpg because the engine is sized for steady state driving. The electric motors are there to give additional acceleration when necessary and to provide power when the power demand is so low that even the efficient Atkinson cycle Prius engine would be inefficient. Using the battery too much causes the engine to run more to keep the battery charged due to the energy conversion loss as energy goes from mechanical to electrical and back to mechanical.































For a more in-depth discussion, join one of the Yahoo Prius groups.































This site has an in-depth look at how the 2001 Prius works. The later Prius use the same basic concept, but the numbers are different. Click on "Understanding your Prius".































http://www.ecrostech.com/prius/original/PriusFrames.htm































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The regenerative braking supplies only a small part of the electrical generation. Most electricity is created from the two motor/generators (MG) that always work in opposition to each other when the Prius is in motion. One is generating and the other is powering. Which does which depends on conditions.

Yardjass

I'm no prius driver but I am an engineer who worked on an one-off hybrid SUV build. The Prius still uses NiMH batteries, correct? Or did they switch to Lithium Polymer? Regardless, both types of batteries are shipped from the factory and/or stored in a partially charged state. I don't recall the exact reason for this but I think it has something to do with better voltage balancing between the cells. Let's just say EE is not my territory. What is likely happening is your car is charging up its batteries, again I am not sure what the prius uses other than regen-braking. Well, I guess they have those neat little solar panels on them that they claim can power the AC by themselves. I highly doubt that but they do add something. Likely either an alternator or charger ultimately links up to the engine. Tire pressure can give you a couple of added miles per gallon, not increase your MPG by 50%. If your tire pressure was off enough to affect the mileage that much, you would be able to tell just by looking at the sagging wheels and even then I'm not so sure it is possible. I think you're just excited that you got a new car and can't wait to test it out (I would be too lol). Just be patient and give it a few weeks of driving around to let everything break in and the batteries to get some juice in them and then see what happens. I think you will find that things are working as they should. If not, factory defects do happen from time to time and that may be your problem. Work with your dealership and I am sure they can get things fixed up for you. Good luck!















































I think I forgot to state the reason for reduced mileage. Energy contained in the fuel is extracted by combustion in the engine and delivered to the wheels, the high voltage battery for driving and the 12 volt for things like lights, speakers, etc. If you start at say, half charge, more of this energy has to go into charging the high voltage batteries up than normal and this energy comes from the combustion in the engine which comes from the fuel in the tank.































So, more charge requirement = more fuel requirement = sub-par mileage















































Yes, regen braking does not supply all of your power or even close. The engine powers either 1.an electric generator or 2. a regular alternator that in turn powers a charger. This means that all of your power starts out from the engine except for the small amount gathered from the solar panels. The regen braking works on the concept that if you drive an electric motor backwards, it produces power but you will never gain all of your kinetic (moving) energy back from this because some is lost due to heat and friction between car parts, the road, etc.































Focusing on the highway isn't going to do you any good either. A parallel hybrid like the prius's weak point is the highway. An engine is most wasteful in "stop and go" traffic and your batteries and electric motor take care of this and they do it without the engine having to turn on at all in many cases. By purring around at a low RPM on the highway, the engine can charge the batteries while it is running more efficiently than around town. You can't go at low speed forever without running out of juice and when things start to get tight, your engine will kick on to help drive the car and charge the batteries back up to an appropriate charge state. This is what I suspect is happening with your vehicle and why I suspect that it will go away shortly. You may also have a dead or low functioning cell in your pack, which would make the car's control system think that it is never charged up and keep the engine on at all times.















































Another thing you want to keep in mind is that this "mechanical to electric and back to mechanical" is not wasteful compared to a combustion engine in changing driving conditions. You will only get about 20% efficiency on average (percent energy in the fuel that is actually utilized) compared to up to 95% for some electric motors. This efficiency goes down when you are in "stop and go" traffic to the point where it is actually better to use electricity obtained running the engine at highway rpm's supplemented with the regen braking and the solar than to just use the engine by itself. For more on this, check out series hybrids like the Volt. They work by 1. going a certain distance, usually 20 to 40 miles on a plug-in charge and 2. Running an engine at its "sweet spot" for efficiency when it is on. This is possible because the engine is not mechanically linked to the wheels. By doing this, it can obtain maximum efficiency while using its energy to charge a battery that runs the car's electric motor. One might think that this mechanical to electrical conversion would be less efficient than a standard gas car that is purely mechanical but it is obviously not either