Prius Sudden Fuel Economy Decrease

Discussion in 'Fuel Economy' started by dkoler, Nov 18, 2008.

  1. dkoler

    dkoler New Member

    Hello -
    We were averaging 48-49 mpg for about the first year on our 2007 Prius. Immediately after our regular dealer service, mileage dropped down to 39-40. No other changes were made. Even with my best pulse and glide efforts, I can't get past 41 now for any significant time, and we actually get better mileage on the highway than around town now. It seems like we have more drag on the glide now, and it's rare that we are able to get the battery level up to the green bar, despite accumulating many car icons in the bar graph screen. Toyota says everything is fine and checks out - "lots of drivers get less than 40 mpg." I wonder if our battery is charging/functioning properly despite Toyota's assurances. Another problem is the fuel tank-bladder is not allowing us a full fill-up, even though we already had it replaced once. Thanks for any advice you can share.
  2. brick

    brick Answers to "that guy."

    The first thing to check is the oil level. It is still common for a dealer to over-fill the crank case which can have some impact on FE. Could you check your invoice and provide a list of services that they performed? That would help us make suggestions rather than listing everything that can impact FE (and there are lots!)
  3. mparrish

    mparrish Rosie the Riveter Redux

    Where are you? The best thing to do is:

    (1) Live near somebody in this community.
    (2) Let that person take it out for a spin.

    It's either the driver or the car, and (2) will help answer that. glides have much more drag now that winter is coming. Did it get a lot colder at the same time you took it in?

    The full fillup is becomes a thing of the past as winter takes its toll on the bladder. That part makes sense.
  4. CitrusInsighter

    CitrusInsighter Well-Known Member

    The other common thing for dealers to mess up (or in their minds "correct") is your tire pressure. If you were running them over 40 psi, its very likely that the dealer took them down to 35 or even as low as 30 psi. I'd check your pressure immediately and take them back up to 44 psi (max sidewall) if they're not there already.

    Now your drop in FE sounds like more than just tire pressure, but there's a good bet that that's contributing too. Also, have you had the car for a full year yet or is this the car's first winter? If this is the first time driving in colder weather after getting used to driving the car, that may account for some of the drop off.
  5. Harold

    Harold Well-Known Member

    Did they put 0-20 wt oil in? They may have dumped 10-30 into it. Check tire pressure as well! They did something wrong. H
  6. msirach

    msirach Well-Known Member

    I guarantee that they dropped the tire pressure if you had them elevated any. And the weight and level of the oil is a definite possibility.
  7. BudgetFitting

    BudgetFitting FAS Convert

    Like stated above, dealers will lower tire pressure if it is above the car maker's recommendation. Check the tire pressure.
  8. dkoler

    dkoler New Member

    Thanks for the responses. In response to the questions, I can add:
    1. The service was done in mid-July and included LOF (they used 5W20), and repair and replace "combination meter assembly" in response to our complaint that the fuel guage did not seem to be reading correctly.
    2. They did reduce the tire pressure, but I bumped it back up to max almost immediately when I saw the mileage had gone south. The decreased mileage happened immediately in the hottest part of the summer.
    3. We had already gone through the winter of 07-08 with the car and did experience decreased mileage down to around 41-42 while it was cold. It hasn't really gotten cold yet, just chilly, so we're expecting mpg to drop some more as it gets colder.
    4. We live in the Coeur d'Alene, Idaho area and I'd love to have an experienced hybrid driver test drive our rig and/or critique our hybrid driving.
    Thanks again for any comments or suggestions!
  9. Tochatihu

    Tochatihu Well-Known Member

    Here' san uncommon one, but it does happen. The rear disk brakes are now dragging, because the cable tension was reset (wrongly) or the pedal is down one click. The simple test for this is to drive a mile or 2 from cold, then stop and do a wet finger test on each rear brake drum. Any notable heat means the shoes are dragging, and it doesn't take much drag to take 10% off the mpg.

  10. Taliesin

    Taliesin Well-Known Member

    Reminding me of something else to check, the parking brake may have been tightened, causing the same brake problem.

    I find this problem very common, but I am not sure how easy it is to adjust the parking brake on the Prius (our vehicles here at work are super easy to adjust, and people are always tightening them too much or loosening them too much so that they don't work at all).
  11. Maxx

    Maxx He who posts articles

    I bet they put non-synth oil in. I know my girlfriends Jetta TDI is VERY sensitive to regular oil - if you don't use synth it will severly hamper performance noticabley and mileage suffers. I would think that a 1.5L motor pushing that much car would suffer similarly.
  12. Mendel Leisk

    Mendel Leisk 2010 Prius (CAN Touring) Staff Member

    I'd second parking brake adjustment. Whenever our (Honda) dealership does a brake service it comes back with parking brake that fully locks at 3~4 clicks. Shop Manual spec. is 8~10 clicks.

    Does your rolling resistance seem greater? For example, when you're rolling up to a red light on level road, how does it compare to the past.

    Maybe jack up the back end, release/engage/release the parking brake, and then try spinning the wheels by hand. There might be a whisper, but they should be fairly free wheeling.

    If you can determine if and where the parking brake adjustment is on your car, and can get your hands on the Shop Manual spec., you should be able to remedy it.

    As a rule of thumb: there should be little or zero drag with parking brake released, and the very slightest increase in drag at one click.

    BTW, I'd also second engine oil overfilling by dealership as another potential culprit, dealerships overfilling engine oil is the norm in my experience. I believe optimum oil level would be around 2/3 of the way up from the low to full mark, and definitely not over the full mark, but explain that to the dealerships. I can kind of see their mentality, they're providing a product, and feel a (misguided) obligation to provide full measure.

    With our Honda HCHII '06, the oil spec is 3.0/3.2 liter without/with filter change. Up to now the dealership has been consitantly dumping in a full four liters, and changing filter at each interval, when Honda spec. is only change filter at alternate oil changes.

    I'm likely going to do my own oil changes from here on: more control, less inconvenience, definitely cheaper. It's not a good idea to walk away from your dealership's service department completely though. You might let them do the brake jobs, and deal with the oil changes yourself (and keep them posted, so that they update their records for the oil changes). It's beneficial to keep in-touch with dealership service department: They are "pros", and are aware of service bulletins, etc.
    Last edited: Nov 22, 2008

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