Possibly Poor Prius Performance

Discussion in 'Toyota' started by jss, Jan 3, 2009.

  1. jss

    jss Member

    I'm a newbie - to the site and the Prius. I bought a 2009 Prius two weeks ago. According to the MPG display I'm getting <23 MPG. I only drive ~6-7 miles/day, and have only filled the tank once. I live in a hilly city that's been in the 20's - 30's F. The Toyota dealer told me that the MPG display is unreliable and that I should go by miles between fill-ups and how much gas I need to fill the tank.

  2. JusBringIt

    JusBringIt Be Inspired

    Hello Jss and welcome to cleanmpg. I can assure you that you would have to work extra hard and purposefully be trying to set a track speed record in order to get <25mpg in your prius. I do not own one but there are plenty of members here who do who can help you achieve 3 times what your current consumption display says. Your car needs some break-in time as well. The ifcd may be off also, so fuel consumption should be calculated at the end of the tank by dividing miles driven by fuel used to fill up.

    Good luck!
  3. Chuck

    Chuck just the messenger

    Welcome to CleanMPG!

    Some Prius drivers will be around soon, but hills are a killer.

    The difference for me driving at 80F and 20F is at least 15%.

    If you put your 6-7 miles in one trip, your Prius is getting warmed up - maybe.

    While you can improve on this by doint things like moderating your speed and accelerations, your fuel economy will definitely be better on a highway at 50-60mph on a warm day.
  4. jss

    jss Member

    Thanks JusBringIt and Delta Flyer. If I'm understanding right, it sounds like the iFCD may be "off," but would it really be that far off? And would 23 MPG be possible in a Prius, even if only 3 miles are driven in cold weather? Thanks again for your help.
  5. JusBringIt

    JusBringIt Be Inspired

    I know of this lady that was getting 14mpg in her honda accord rated for high 20's combined. What I know is that if you let your car sit and warm up for 10-15 minutes, you are in a hilly area, and mostly accelerating, then it is possible, especially since your commute is so short. What did you get in your previous vehicle? also, what year/make/model?
  6. diamondlarry

    diamondlarry Super MPG Man/god :D

    Welcome to CleanMPG. 23 mpg does seem a bit low but, you have to remember that you and the car are both learning. Also, as Ricardo mentioned, it will take some time for the car to break in. The tires alone can take ~1000 miles until they reach a state where they are ready to deliver maximum efficiency. I would also say that if you haven't already done so, increase your tire psi to the maximum on the tire's sidewall. With the temperatures you are having, a block heater will help tremendously, especially with your shorter trip lengths. Putting the block heater on a timer for 3-4 hours before you leave should be about right.

    The temps in my area have been similar to yours and even lower here and I have been regularly averaging in the 60's with a daily commute of 22 miles round trip. Keep reading and be sure to ask us lots of questions and those numbers will rise steadily.
  7. mparrish

    mparrish Rosie the Riveter Redux


    If you purchase and install the "big 3" (engine block heater (EBH), EV button, scangauge), you'll be in the 50s in no time. Search for those 3 items. Start with the EBH. You want to leave with your ICE a toasty 110F, not 20F.
  8. jss

    jss Member

    I had a 2003 X-Type (AWD) Jag and was getting ~16 MPG. I guess I'd heard that a Prius would never get less than 40 MPG, so I was kind of surprised with 23 MPG.
  9. jss

    jss Member

    It sounds like warming up the engine (either with an EBH or just idling) might be a good first test to see about getting better mileage?
  10. JusBringIt

    JusBringIt Be Inspired

    I have a hunch your Ifcd is a bit low, however, you should notice an increase in your gas mileage over time. I am confident you'll be up t to 50mpg in no time if you you stick around here ;)
  11. donee

    donee Well-Known Member

    Hi Jss,

    Over on Prius chat several people have done long term studies of the true gas mileage. They all found that the MPG meter on the Prius is within a few percent of the true mileage, and the by-fill-up method can vary as much as 20 percent on a single fill evaluation. This is due to the rubber bladder in the Prius gas tank.

    So, if its says 23 mpg, it probably is getting that. But remember to hit reset at each fill to evaluate the mileage for the next tank of gas, independant of the previous mileage.

    For that poor a mileage, the first thing to check is if the rear brakes are rusted. Do you park outside on a non-paved driveway or dirt road? Do you park next to a curb which gets periods of high water or salty slush? That could corrode up a rear brake that is tight from being new pretty quick. Have them get the car on a lift and rotate all the wheels, they should all turn freely.

    Second would be oil level. It should be below the top mark on the stick. If its not, it can screw up the MAF (Mass Airflow Sensor), which may need to be cleaned.

    Next is tire air presure. Despite what the door panel says, the best pressure for a Prius is 42/40 psi (Front/Back) cold test pressure. This is where the tires wear even across the patch, so that is where the best traction is. And its also good for fuel economy to have the tires at that pressure. If you had the tires set at say something like 32 PSI on a 80 degree delivery day, and have not adjusted them since, they will be down to 26 PSI now at 20 F. 1 PSI per 10 F is the rule of thumb for tire pressures. 26 PSI would definately do a wammy on your mileage.

    What tires do you have? Some people have complained about poor mileage after taking delivery with 17 inch rim wide performance tires. This will definately do in the mileage.

    Short trips in cold weather can be a general problem. If your running the heater for that time at something like 70 F, well, the engine will not shut off, and the car will use gas as if its regular car. If you end up in 3 or 4, 3 minute stop lights during that trip, well, that is just going to use gas. The Climate control can be confusing to get used to. When you come to your first stop, turn off the climate auto matic control. If your stopped there for more than 30 seconds, the engine will go off. For such a short trip, unless your defrosting the windows, using the heater is self-defeating. The car wont warm up in that short a time, you got your coat on, so you wont feel cold anyway, and the engine will be slowed from its warm up. Crack the left front window about 1/8 of an inch, and the right rear about 1/4 to keep condensation out of the car over time for these short trips.

    We experienced winter Prius drivers will grill block below freezing. Block off the upper grill slits, and 3/4's of the lower grill (on the passenger side) for short trips in below freezing weather. This will help get the engine up to hybrid mode temperature quicker. This is commonly done with water pipe insulation tubing. Its about 1/2 inch thick polyethylene foam tube with a bonded slit. Hardware stores, etc, have it. Seperate the bond, and push both edges into the grill slots. You will need to slice the foam to get it to grab onto the vertical bars that are down inside the grill.

    When you say hilly, how long are these hills? Are you going down hill for miles? Or maybe a mile at max. If your not in the mountains, you wont need to use the B mode of the transmission. So, if your using that, that could be a problem too. Because the car will be using engine braking downhill, rather than battery regeneration (electric) braking. Which again, is just a waste of gas.

    Finally, you may need a wheelalignment. Its possible the trip over from Japan this time of year was on rough ocean. And the car tires are chained down to the the deck. But there is nothing holding the body from moving. As this is not the designed method for the car suspension to work, it can wrench the alignment adjustments. Toyota offers a free alignment for the first year to take care of this situation.

    Also, I am talking about the average mileage, not the instaneous fuel economy. The instantaneous fuel economy can dip to as low as 8 mpg during accellerations. But as you get up to cruise it will go way up into the 50's or so.

    Yes, there are some pedal manipulation to learn with the Prius, that is different from other cars. But this is enough for you to check out first.

    A common way to confirm the car is OK, once you go through all this, is to take the car out on a highway trip of about 20 miles. Put the car in cruise control at 60 mph, on a calm day, reset the mileage meter, and see if it does better than 50 mpg in warm weather, our about 50 mpg in this weather. Yes, you can use the heater for this run. Set it at 65 F. Best to run the car around locally till its warmed up about 10 miles before the test.
    Last edited: Jan 3, 2009
  12. SentraSE-R

    SentraSE-R Pishtaco

    I think 23 mpg is entirely possible in a Prius, if you're a lead-footed driver. I volunteered in Bryce Canyon National Park last Fall, and for the three previous years, driving a park Prius to many sites. 50-60 mpg was normal for me driving it around. One day, a Ranger and i were working in Cedar Breaks National Monument, about an hour away, and 2000' higher in elevation. He was driving, and I was astonished to notice that EVERY time I looked at the instantaneous mpg display, he was getting under 20 mpg. The man simply had a lead foot, and didn't drive intelligently - certainly not for mileage.
  13. JimboK

    JimboK One owner, low mileage

    There are two potential issues here: an unreliable MFD reading and poor actual fuel economy. My vote is for #2.

    I highly doubt the MFD is substantially off, and the dealer is wrong; the MFD is quite reliable. As Donee says, several of us have tracked the difference between MFD fuel mileage and actual fuel mileage over several tanks. See this for examples, which document that the difference is less than 3%.

    On the other hand, if by some slim chance the MFD is off by, say, 50%, then there is a defect the dealer should fix. You can validate this easily enough be tracking your own differences over several tanks. To reiterate a point Donee makes: Don't rely on the results of just one tank; the Prius' flexible fuel bladder can give you substantial tank-to-tank variation.

    Assuming the MFD is correct, then follow the excellent advice given by the other Prius owners here. Your results are believable in cold weather (presumably with cabin heat), with short trips, and on hilly terrain. (FE in all cars suffers in these conditions, though the effect in the Prius is probably more exaggerated.) Before I added an engine block heater and started hypermiling, it was common to see the first five-minute fuel economy bar on the display in the 20-25 MPG range on a cold winter morning; others report the same. But I still managed low 40s when I first bought the car (in the winter), because my trips were considerably longer than 5 minutes.
  14. JimboK

    JimboK One owner, low mileage

    I missed this in my first reading of the thread. EBH: a definite "yes." Idling: a definite "no." First, the internal combustion engine (ICE) will idle only for a little over a minute after startup before it shuts down, even in the coldest of weather. Second, while it's running, your fuel economy is 0 MPG. Better is to start driving immediately.
  15. jss

    jss Member

    Thank you very much for your incredibly helpful posts. It is great to know that good people are so interested in helping others. I look forward to contributing as I learn more!
  16. Skwyre7

    Skwyre7 Well-Known Member

    I think we have missed a big issue here. jss only drives about 3 miles at a time in cold weather. The Prius never has a chance to warm up, so the 23 MPG is very likely.

    jss, the EBH will definitely help. Add to it a SG and a grill block, and you should be getting close to double your mileage without much effort. In the meantime, take it on a long drive (maybe an hour) and see if that helps things. I bet once you get it warmed up, you'll be up in the 40-50+ MPG range no problem.
  17. JusBringIt

    JusBringIt Be Inspired

    If his jag can manage 16 mpg which is the city rating for that car, I'm sure the prius is capable of much more regardless of warm up. That is like my car getting 9 miles per gallon. Regardless of how cold my car is, that will never happen. impossible. My instantaneous mpg on a rapid pulse in 3rd gear starts at 8.xmpg and goes up to 14mpg when its freezing out. I usually am at about 12mpg after the first 3/4mile. THis is just some sort of a comparison and I'm not saying they're completely linear, just trying to stay within some sense of reality here. I would believe 35mpg, but 23 is a bit hard to swallow.
  18. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Ricardo, you are missing how the vehicle works. When it first starts out the vehicle runs on the electric motor and idles the engine to get the cat warmed up -- this can last for 2-3min and it is quite common to see low 20's or worse during this time period. Also, recall that much of the Prius rating is dependent upon its built in hybrid functionality -- functionality that doesn't even exist until the vehicle is warmed up. So no engine off, no EV only propulsion, no P&G, nothing but high RPM engine to get things warmed up. Throw some hills in the way and it will simply suck compared to its EPA ratings.
  19. diamondlarry

    diamondlarry Super MPG Man/god :D

    It may be due to my commute but, it is quite common to be way over 50 mpg at the 3 mile mark. Lately it has been right close to 60 mpg at the 3 mile mark but has been as high as ~100 mpg in the summer at the same point. I will say that due to my EBH I can reach S3(155F and above coolant) in ~1/4-1/2 miles.
  20. mparrish

    mparrish Rosie the Riveter Redux

    Oh, it is brutal....even if the cause is worthwhile. Happiest day of my life was watching S1 drop to a mere 20 seconds or so after installing the EBH & EV button.

    OK, happiest day was seeing my son born. But minimizing S1 is a close second! ;)

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