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Drop in fuel economy after a my Prius took a bump :(

Discussion in 'Gen 3 Prius Fuel Economy' started by Solrz, Feb 8, 2015.

  1. Solrz

    Solrz New Member

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    So, I purchased my Gen iii Prius almost a year ago on 21/02/14 and it's been great! Until now that is..

    A bit of background as I am a newbie to the forum. I purchased it with 42341 miles on the clock and just this evening when I got out of the car the odometer read 82019 - so I've travelled a few miles and spent quite some time in the cabin. When I purchased it I reset the trip A so I could monitor my mileage and although it's not perfect as it resets every 9999 miles it carries forward the MPG which currently stands at 60.5 over the 40k miles that I've nearly driven. I reset trip B after every fill up so I can see how I'm managing each tank of fuel. I don't drive the same route everyday and week. nor do I travel the same distance daily but somehow each week it averages at around 800-900 miles. Just before my "incident" I had just changed my tyres all round to Dunlop Sportmaxx RT which came with a C for Rolling Resistance, A for Wet Grip and 67 dB. After doing so I noticed that my fuel economy on trip B was starting to rise and the latest came out at 64.7 MPG. I was really looking forward to getting some great mileage.

    Okay, I'll cut to the chase. So, two weeks ago whilst reversing onto a clients driveway the pavement rose up slightly and the clients driveway sloped downwards. I didn't quite notice that at the time so as I backed onto their drive the bottom of my car made an almighty scraping sound on the pavement. The scraping sound came from the area either immediately behind the front wheels or perhaps immediately in front of them. In my head I thought it must be either the exhaust or oil sump. I immediately stopped however I knew that the damage may have already been done and either needed to carry on reversing or drive forwards. I decided to drive forwards and parked up on the road. My car had taken a chunk of tarmac out of the pavement approximately 3 inches wide and a 1/2 deep. After waiting for some time there was no leaking oil and still isn't any. However I've been driving around for two weeks since then and my fuel economy over the last 4 fill ups has been consecutively low around the 54-55 MPG area - and that's with my best driving behaviour to increase fuel economy whereas beforehand I wasn't trying as hard. I finally managed to get into a garage on Friday who lifted it up and had a look at the entire underside. They brought me round to show me whilst it was up in the air. There's not a mark on the underside. No visual signs of damage or movement to any of the underside components. The only piece that was out of place was one of the plastic under engine covers at the very front of the car which was far from the suspected area and had a button clip missing which they replaced for me.

    So this leaves me looking like I'm imagining things... But I'm not! There's something wrong with my poor Prius. I want to get it back above the 60 MPG and fix whatever it is that I've done wrong to it. Could it be the catalytic converter? The scrape that the car took certainly did something wrong but I just don't know what it could be. I'm considering taking it to Toyota to run one of their diagnostic tests but I'm not sure what that will show up and if it will show up what I did to it.

    Any help would be greatly appreciated as it's so frustrating knowing what my car is capable of and not being able to achieve it because I've buggered it up somehow.

    - Have you read This Thead Yet?
    Yep

    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
    60.5 Mpg based on my trip A reading which has carried almost 40k

    - What fuel economy are you expecting and why?
    60+ Mpg

    - What are the approximate outside air temps?
    10C

    - How long are your trips?
    At least an hour to reach each destination

    How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)
    Not sure, I will check and update or post

    Have you had your alignment checked? Any pulling or abnormal tire wear?
    I noticed a slight pulling to the left almost 3 months ago. It has changed or gotten any worse and I don't believe that it's the cause of the problem however it's booked in to be aligned next week so I'll update.

    - How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?
    If my weekly average is 800 miles; 500 on motorway cruising at 70 mph, 300 on dual carriageways cruising at 40-50 mph and 100 miles driving through the city at around 30 mph

    On a separate note, I use cruise control as much as possible and one thing that I find annoying is that I cannot set it at 20 MPH which would be really useful in city areas where speed cameras are constantly around. If anyone knows how to do that please let me know.

    - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)
    It really is a mixture which is why I think my MPG used to be quite well balanced over the many miles that I travel

    - What are your tire pressures?
    42 PSi at the front and 41 PSi at the back, or whatever it says on the sticker on the drivers side door jamb

    - Is your oil overfilled? (i.e. above the full mark on the dipstick)
    It's just over 3/4 filled but not quite full.

    - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
    BMW 320d which gave me around 42-44 mpg

    - What region/state are you in? (if you haven't set your location)
    London, UK

    - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?
    As sensible as possible without driving too slowly or holding people up behind me. I try and use the electric mode and pulse or glide when I can and allow the car to slow down on it's own whenever I can for as long as possible.

    - What modes are you using, if any? "normal", EV, power, eco?
    It's been in ECO mode around 95% of the time

    - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?
    Not as often as I should which I will now start doing.

    - Are you driving using D or B mode?
    I use D mode for driving. I have tried experimenting with B to slow down on hills or quickly when I need to, although I don't know if its good to use in general to save braking so I'll read up on that.

    - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?
    No AC, just the heater or fan. Temperature on auto set to 22c

    - Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).
    Dunlop Sortmaxx RT
    C Rolling Resistance
    A Wet Grip
    67dB

    - If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
    I scraped the underside of my car which I believe to have almost immediately caused my drop in mpg :(

    Read more: Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat
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  2. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Speculation, if the cover dropped down it could act like a parachute increasing drag. But the gouge has me scratching my head. Muffler comes to mind, possibly tail pipe. Unless you added a towing hitch, there isn't a lot other than bumper covers that might scrape bottom.

    It would be nice to know if it is low-speed, high-speed or both by running two, bi-directional benchmarks: ~35 and ~70 mph. I am assuming these are Imperial gallons and degrees C.

    Bob Wilson
     
  3. Solrz

    Solrz New Member

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    Hi Bob, thanks for your response!

    I don't think it was the tail pipe as all the brackets and the entire exhaust system was intact and mark free when the garage put it up on the ramp to take a look at it. The sound came from below the drivers seat as it is that area which I made contact with the pavement. I'm really baffled though as I saw with my own eyes that there wasn't a single scratch or mark on the underside that was new and indicating to be the culprit to my increase in fuel consumption.

    When you say low speed and high speed benchmarks are you referring to running mpg consumption tests at both low and high speeds? I don't mind doing something like that although it needs to fit around my work diary. I have a 51 mile journey to my first client tomorrow morning of which 40 miles will be at 70 mph and the remaining will be at 30-40 mph. Then my next client is 38 miles from the first, again travelling 70 mph for 25 miles of the journey and around 30-40 mph for the remainder.

    Sorry, I've just learnt that our gallons are different to yours. That explains why my mpg looks deceptively higher that what other people are achieving on here.... and here was me thinking that I just drove extra efficiently :)
     
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Not to worry, I'm used to doing the conversions. They key to a benchmark:
    • no change in altitude - why we like to run both direction to take out even small elevation changes
    • factor out wind effects - not perfect, good enough
    I prefer 10 miles each way, warmed up Prius, using cruise control. Then compare to this:
    http://hiwaay.net/~bzwilson/prius/pri_2010_800.jpg
    (Multiply my MPG by ~1.2 to convert to Imperial.)

    Bob Wilson
     
    #4 bwilson4web, Feb 8, 2015
    Last edited: Feb 8, 2015
  5. ursle

    ursle Gas miser

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    an 09' a thunk. The 12v got moved a little and lost a bit of ground, it's weak and getting weaker.

    An obd2 reader for anything unusual might not hurt, if it's free.
     
  6. bisco

    bisco cookie crumbler

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    there's another recent thread with similar loss of mpg's. in the end, they went into the menu and reset something, and the mpg's came back. maybe a last resort if you can't find anything wrong. the member is 'SvMi' and the thread title is 'engine question - inspect or not?' all the best!(y)
     
    #6 bisco, Feb 8, 2015
    Last edited: Feb 8, 2015
  7. fuzzy1

    fuzzy1 Senior Member

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    Don't overuse the EV button, it will hurt MPG. You should be able to great results without using it at all.
    Don't take the question as a suggestion that you should be warming up.
    B is useful to prevent brake overheating, and possibly wear, on long steep downhills. It won't help MPG. If you can get the braking you need with the pedal in regeneration mode, without filling up the traction battery, then B will provide no advantage.
     
  8. Solrz

    Solrz New Member

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    Thanks, I've just ordered an odb2 reader as they're quite cheap and it would be useful to have one around.
     
  9. Solrz

    Solrz New Member

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    Thanks for your reply.

    I actually don't use electric only mode, what I meant was I use the electric engine as much as I can in slow moving traffic and in city driving where heavy acceleration isn't necessary.

    Thanks for your explanation of engine braking. I won't bother using it, I'm better off timing my braking to help regeneration.
     
  10. The Electric Me

    The Electric Me Go Speed Go!

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    My instinct is to simply tell you that you don't have a problem.

    Because I'm wondering if you simply aren't experiencing the often times "normal" loss of MPG when tires are changed. Even though you claim you immediately saw an increase, it's more typical, in more cases, especially with "brand new" tires, to see a decrease.

    I read that you believe you have noticed a "slight pulling to the left" although you don't think this is the cause of your problem. I think given new tires mounted, and a possible "bump" or scraping, getting the alignment checked is a good idea.

    If everything checks out. I just might not panic, and ride on these tires for a while and see what direction the MPG go...even though you have had 4 fill-ups, it's only been 2 weeks. And I suspect something related to alignment or new tires more than I suspect the undercarriage scrape.

    Best of luck.
     
  11. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Doors and hatch left open whilst vehicle was being repaired running the 12v low or flat. Since jump started before hand over and now car is struggling to charge it or because of it's age it's now damaged and needs replacing?

    Check the 12v using the systems widely advised on this forum before and see if your issue starts there. If it's the original 12v it'd probably be ready for changing anyway.
     
  12. Solrz

    Solrz New Member

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    Thanks for your comments. I hope that you're right and it's just a normal swing of drop in mpg.

    With regards to new tyres performing worse for fuel economy, I assume that you mean that they need a chance to wear in before they start delivering better fuel economy. I'd agree with this that they do need a chance to wear in, however I drive around 800 miles per week so they should have done so by now. Looking at the vehicle maintenance for tyre replacement as I reset it when I had new tyres put on, it's saying that I've now driven 2,268 miles these wheels so they should be worn in by now.

    I'll be getting the alignment sorted this week. I hope that it resolves my issue as that would be great.

    I'm also going to test the 12v battery level as the engine seems to be kicking in more often than I think it needs to when using the electric motor to drive at slow acceleration. My car is now 5 years old so I don't know if it's still the original battery or not but perhaps it does need a change. Hopefully the odb2 reader can tell me what the charge is otherwise I'll have to invest in a volt meter.
     
  13. Solrz

    Solrz New Member

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    Okay, so I've figured out how to put my prius into vehicle diagnosis mode / service menu.

    I went to "function check/setting" and then "vehicle signal".

    My battery is 14.0v

    When I turn my lights on nothing changed

    When I window all four windows up and down the level changes to 13.9v and then returns to 14.0v

    When I softly pressed the accelerator to fire up the engine the level momentarily changes to 13.9v then returns to 14.0v

    I'll do some more research on battery levels and for a healthy battery but those readings seem to be okay to me at first glance.
     
  14. The Electric Me

    The Electric Me Go Speed Go!

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    I'll admit my ignorance and say, I simply don't know what a "C" for rolling resistance means in relationship to tires.

    Generally in the USA "C" means satisfactory. Not the best, not the worst.

    If these new tires are simply not designed to be as Low Rolling Resistance as the set you had on before, that could explain the drop in MPG even after a break in period.
     
  15. Solrz

    Solrz New Member

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    Hi again!

    You're quite right, C isn't great for fuel economy its just somewhere in between.

    However the previous set that were on the car were budget tyres that the dealer had put on when they sold the car to me. I found the rolling resistance rating for them online to be an E rating so I was expecting better performance with the Dunlop set that I chose.
     
  16. fuzzy1

    fuzzy1 Senior Member

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    That is not the battery voltage, it is the voltage of the inverter feeding the battery and 12V system. You must have been in 'Ready' mode.

    To see the battery voltage, do the same test in ACC (accessory) mode, which leaves the inverter shut down. The most meaningful result will come from doing this test first thing in the morning, before putting the car into 'Ready', but meaningful results can be had a few hours after the car was last run. Once the car goes 'Ready' and the 12V battery gets some charging time, the battery gets a temporary lift, and it takes considerable time to relax back to its natural level.
     
  17. Solrz

    Solrz New Member

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    T

    Thanks Fuzzy1! I turned off the Prius and pressed the on button without touching the brake pedal and went into the same menu. This time my battery reading is different.

    It's currently reading 11.9v

    If I turn my headlights on then it drops to 11.5v
     
  18. GregP507

    GregP507 Senior Member

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    Everyone loves a mystery, and I don't want to speculate on what I think is causing it, but there are several things to consider in troubleshooting this problem:
    • Is it really a problem? Is the reduced mileage verifiable and repeatable? Could it be due to colder weather?
    • Where is the energy being lost? Do you have any abnormally high temperatures anywhere? Try using an IR thermometer after you drive it.
    • Do you have abnormal tire wear?
    • Did you get a bad tank of fuel? It happens more than most of us think.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    That is low. Try it again after the car sits for a few hours, to see whether or not it goes lower.

    At that number, some will declare it too low. But I'm not fully convinced, because it seems that the low battery / low MPG issues that were clearly fixed by battery replacement on other Prii had lower voltages than that. Prii are also known for not managing to keep the 12V adequately charged in short trip applications, so if you have a 12V recharger, it may help to put on a slow charge (2 to 4 amps only) overnight. But it appears that you regularly put a lot of time and miles on this car, so that particular issue ought not be present.

    Several new members here have replaced marginal 12V batteries and not fixed their low MPG issue. But GC's point is correct:
     
  20. GregP507

    GregP507 Senior Member

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    I wouldn't worry about replacing the 12V battery until it becomes a risk for not being able to start the vehicle. I think it's irrelevant what the resting battery voltage is, as long as it does it's job, which is to boot the car into ready-mode and to run accessories when the system is off. Personally, I don't use acc-mode, because it's really the only way to run down the battery, which damages it.