Help me get better mileage

Discussion in 'Gen 2 Prius Fuel Economy' started by Stoods, Mar 30, 2011.

  1. Stoods

    Stoods New Member

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    All -

    First off, I know very little about cars. I tend to let other people do the work (ie, the dealership).

    We bought the 07 Prius (touring? It's got the bigger wheels, leather, navi, etc) in May of last year, 19K miles. It was a lease. Certified extended warranty. I think we paid $16500, after the dealer told me he would not go lower than $21K. But that's all an aside.

    I drive 37 miles each way to and from work, about 75 total per day. We had previously achieved around 47-49 mpg on the car. I don't do anything fancy like the pulse and glide I've been reading about- just hit the cruise at 58 mph (it's a two-lane freeway to work and back, not the interstate).

    I got tires a while ago from Les Schwab. They told me that my Prius had a different wheel size, and that they had to put on slightly larger tires than the factory recommendation (higher diameter in the wheel face? I don't remember exactly what). They're great tires, as I can drive through a 3 inch puddle without hydroplaning.

    But, the mileage dropped off significantly. I'm getting about 41-42 mpg right now. I'm guessing that the tires are directly responsible for the drop (although I did have my oil change done at a local shop recently, instead of the dealership - I insisted on synthetic oil, of course).

    What are my options? I don't think I can go back to Les Schwab and have them put different tires on at this point. Also, I feel like the engine is recharging the battery far more often than it used too, but that could just be an artifact of me constantly looking at the touchscreen.

    My friend gets mid-50s on his Prius. I just don't know why I can't get the same on mine!

    (PS: Our other car, an 09 Honda Fit Sport 5AT that my wife drives, gets 46 mpg on the same drive.)
     
  2. bisco

    bisco cookie crumbler

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    :welcome: check your tire pressure and oil level. how many miles on the new tires? what brand and model? your friend probably has less freeway on his commute.
     
  3. mikewithaprius

    mikewithaprius New Member

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    It sounds like you got 17" tires instead of 15" that come with the car, which will lower your mileage only a teeny bit (1 mpg...). Newer tires will give you a hit, but it sounds excessive. You probably got a tire that's not low rolling resistance. A low rolling resistance tire keeps moving more easily to preserve momentum, and thus the car works less. You may not be able to do anything about it other than get new tires, but that price would outweigh any mileage gains.

    Search on this forum or google for Prius tires, lots of people have talked about it. A popular choice seems to be Goodyear Assurance Fuel Max.

    For other mileage techniques, given the speed you travel typically, you should learn about warp stealth, a no-fuel mode over 42 mph that keeps the engine going at minimal RPM. It's very good for downhills or when your exit is coming up and you have to slow gradually anyway. Scroll down on this page: Pulse and Glide plus Warp Stealth in the Prius II for maximum FE … - CleanMPG Forums
     
  4. Stoods

    Stoods New Member

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    I'll have to check the type of tire when I get outside next. I'm guessing the pressure isn't at max, but I'm worried about safety (it rains a lot here in the pacific northwest). Does a higher tire pressure necessarily mean I'll lose some traction ability?

    The oil was filled up to the dot on the dipstick with 5w20 synth when I got the change done last. I think the guy said he put in 2.9 quarts?
     
  5. bisco

    bisco cookie crumbler

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    as long as it's not above the full line your fine. higher pressure will reduce traction a bit. maybe go up a few pounds? it might just be the type of tire as mike says above. also, it's possible your 12v battery is going bad. how many miles on the new tires? there is a break in period.
     
  6. mikewithaprius

    mikewithaprius New Member

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    Synthetic oil should get you higher mpg, that seems odd. He must have meant 3.9 quarts probably. If you got that at the same time as the tires, it's tough to know which variable did it, but maybe it's slightly overfilled(?), which would account for reduced mpg. It may actually be a little much, like bisco said, shouldn't be over top dot, and most say on a Prius it should be slightly below top dot of dipstick.

    Air pressure best thing to check first before getting dirty/paying someone to check on anything. Rain and snow and everything in between this winter, I was fine at 41 front psi/39 rear psi, I wouldn't worry about slightly higher psi and traction.
     
  7. Stoods

    Stoods New Member

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    I'll boost the air pressure to 42/40, assuming the tires can take that much.

    Re: oil - do I need to check it with the engine warm? If it's "above" the dot, I'm guessing to let some out I'll need to get under the car and pull the oil plug (where ever that is!) to let some out?

    How do I check the battery? Can a parts store do this? I need to get an air filter, so hopefully I can do both at once?
     
  8. Stoods

    Stoods New Member

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    Mike - I'm blown away by your blog and how you average 60 mpg +. That's incredible.
     
  9. bisco

    bisco cookie crumbler

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    air filter! good point, that's another thing. warm the car up, 20 min. or more of driving, park on a level spot, shut it off and let it sit for 5 minutes for the oil to drain down. check the level by pulling out the dipstick (careful it's hot!) wipe it with a clean rag and insert and remove and note the oil level. you may need the right lighting or something behind it to see new oil properly. you can check it cold too, it's just drained downn a little more and will read a bit higher. there is a battery check in the mfd, you can search for it or someone will post the link to the thread.
     
  10. ksstathead

    ksstathead Active Member

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    The old, smaller tires were going around more times per mile. Car doesn't know how far you went, just counts revolutions at an assumed tire size.

    Try finding the rev/mile for your new tires and the old tires (tirerack?).

    Then adjust reported miles by by oldrevs/newrevs.
     
  11. mikewithaprius

    mikewithaprius New Member

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    Thanks Stoods, you'll find some others on here are able to do better...

    Although you'll likely find all the answers by the time I'm done, I'm working on a post for "normal" drivers to try all the little mileage tricks in their daily routine while still going with traffic. Plenty of other people have done this, especially for newer model Prii, but I've found at work there's a bunch of people with Prii who, like me, have little background in cars but, unlike me, don't have the time to sit down and read the entire internet to figure the Prius thing out :) I'll send you the link when I finish.
     
  12. uart

    uart Senior Member

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    It's the tires. There is a combination of three factors.

    1. New tires. (they often give a few percent reduction in MPG while they "break in")

    2. If the rolling circumference is a little larger than stock then it gives a lower indicated MPG.

    3. The larger wheels on the touring edition are more aimed towards performance tires instead of LRR tires. I think they've sold you performance tires without any regard to LRR (low rolling resistance). LRR is important to the Priuses overall efficiency.

    Note that "2" is not a real MPG drop, just an indicated drop based on incorrect odo calibration. But unless they've sold you a grossly oversized tire it shouldn't be more than 1 or 2 percent. Reason "3" will account for most of your MPG drop.

    BTW. That story is VERY common here "New tires and then big MPG drop".

    It's really worthwhile investigating what LRR tires are available in your wheel size. Search the forums here and you'll find some recommended LRR tires. A few that come to mind are :

    Bridgestone Ecopia EP100 (Very Low Resistance)
    Bridgestone Ecopia EP422 (All Weather)
    Hankook Optimo H418
    Michelin Energy Saver A/S
    Michelin Primacy MXV4


    That's not meant to be a full list, just a few to get you started. I think the Michelins are good but pricey, the Hankooks are good value and the EP100 are mid priced and very low rolling resistance.
     
  13. Stoods

    Stoods New Member

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    Wow, I really hope I didn't buy "performance" tires for a car that is designed to be efficient. It's not like I'm going to drag race my prius - although that humorous thought has run through my head more than once.

    Let's say the tires are performance, and bigger than necessary. Let's also assume that I've driven beyond the timeframe where I can bring them back. Am I better off just dealing with them till they're ready for replacement? Or should I buy another set of low resistance tires and use those during the summer?
     
  14. JimN

    JimN Let the games begin!

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    If you're stuck with the tires just ride on them. Inflating to max sidewall pressure should improve the handling. On my Gen2 the Integrities were a bit squirrelly on dry pavement at 45psi. (The yellow idiot light would flash during a stop.) On wet pavement no idiot light.

    Didn't the Touring have 16" wheels?

    Check the 12v battery voltage on the MFD in Maintenance Mode. Just do a search. If it is the original you are due.
     
  15. cwerdna

    cwerdna Senior Member

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    OP, please do get back to us on this, including the exact size of these new tires.

    Even if you replaced the tires w/the exact same model and size, you will likely see a bit of mileage drop, at least initially. See Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires.
    http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.htm

    I'd suggest you check it after the car's been sitting many hours or overnight.
     
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  16. uart

    uart Senior Member

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    First off, post the exact brand/model/size of the tires (eg "Falken Ziex ZE 205/55/R17" for example) so we can stop guessing.

    If you need to change them then they should at least give a prorated refund/trade on the existing tires.

    As for whether or not it's worth doing. Take a conservative estimate of 44 MPG (after they're broken in) versus 48 MPG over an estimated 45000 mile tire life. Do the math and it comes out at over $300.00 saving (more if fuel prices keep rising like i think they will).

    BTW. That's conservative because you can probably do even better than 48 MPG with the right LRR tires. If you want to get over 50 MPG then definitely see if you can get something like the EP100's or EP422's in your wheels size.
     
  17. Stoods

    Stoods New Member

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    Toyo Tourevo ls luxury touring, 205/55r/16 91v

    Is that the right info?
     
  18. uart

    uart Senior Member

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    Yeah that sounds right. They're 16" wheels (not 17") as JimN pointed out above.

    The rolling circumference is 1.7% to 1.8% larger than stock so that only accounts for about 1 MPG (comparatively you're really doing about 1 MPG better than indicated). Also tread-depth probably accounts for another 1% change in circumference, so in total that's about 1.5 MPG indicated difference.

    Also you'll probably pull back another 1 to 2 MPG as the tires break in over the first 5 to 10 k miles. They are probably good all weather tires but perhaps not strictly LRR.
     
  19. Stoods

    Stoods New Member

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    UPDATE:

    I'm not sure how to insert an image, but I wanted to show everyone what increasing the tire pressure did for MPG.

    On the way home last night, I achieved 48.8 mpg over 35 miles, or a 5.7 mpg increase. On the to work today I got slightly less, but I always get worse mileage coming into town. Overall, I'm averaged at 46.5, which is still a 4.4 mpg increase. I tried using some of the techniques I've read about for city driving, as there's a good 6-8 mile stretch coming into town that is 45 MPG with lots of stop lights. Over that 10 minute period, according to the display, I got around 70-75 mpg. I couldn't believe it!

    As to the oil: the reading I took looked like the oil was 1/4 inch above the "top dot." I did three more samples, and they all ranged from slightly below the dot to 1/2 inch above the dot. Am I doing something wrong?
     
  20. uart

    uart Senior Member

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    That's good. Those tires can't be too bad then. :) You might even get another couple of MPG out of them after they break in some more.

    Yeah the car has to be as level as possible to get a good reading. Also the car should have been turned off for long enough for all the oil to drain back to get an accurate level. Wait at least 15 minutes, longer if possible. Also remember to wipe the dipstick first and then re-insert it to get a good reading.
     
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