Reduced mpg in 2008 Prius

Discussion in 'Gen 2 Prius Fuel Economy' started by mmnepps, Aug 24, 2010.

  1. mmnepps

    mmnepps New Member

    Joined:
    Aug 24, 2010
    2
    0
    0
    Location:
    Pennsylvania
    Vehicle:
    2008 Prius
    Model:
    N/A
    Have any 2008 owners experienced reduced mileage without a change in driving habits or patterns? About 9 months back (after about 30,000 miles) mpg dropped from 47-48 to 40-42 (car computer calculations.) I've asked the dealer about it at the last three scheduled maintenance visits and replaced the tires, but they insist everything checks out okay. The dealer always has a "reason" such as the winter blend of gas, driving with air conditioning, too much ethanol in the fuel, etc.. but none of those things had an effect for the first 2 years. Thanks; any thoughts would be appreciated!
     
  2. usbseawolf2000

    usbseawolf2000 HSD PhD

    Joined:
    Sep 22, 2004
    14,487
    2,927
    0
    Location:
    Fort Lee, NJ
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Was the mpg drop before or after new tires? What tire did you get?
     
  3. mmnepps

    mmnepps New Member

    Joined:
    Aug 24, 2010
    2
    0
    0
    Location:
    Pennsylvania
    Vehicle:
    2008 Prius
    Model:
    N/A
    Yokohama P185/65/R15's, after the mileage had dropped.
     
  4. krg03

    krg03 Not expert, just experienced

    Joined:
    Jul 27, 2010
    246
    31
    0
    Location:
    so cal
    Vehicle:
    2007 Prius
    Model:
    II
    Try cleaning the Mass Air Flow sensor under the air filter. Special cleaner for it. Or have the dealer do it (it can be damaged with the wrong cleaner). If your air filter was changed regularly probably not it. Try a tank of higher octane. I used fuel injector cleaner in the gas which reduced my mpg for 2 tanks but after that increased mpg (strange). My AC on/off only makes a difference of 2-3 mpg. Run the diagnostics on the Battery. I've read that can make a big difference in mpg.
     
  5. gdbelden

    gdbelden Gator Hator

    Joined:
    May 29, 2008
    66
    39
    0
    Location:
    Virginia
    Vehicle:
    2008 Prius
    Model:
    N/A
    I too have a 2008 and replaced the crappy integrity OE tires with Yokohama's.

    My mileage dropped from around 45.5 to about 42.5, but it is a MUCH better,smoother, quieter ride. I have only 2 tankfuls of my regular driving (around town) though. May be a break-in period, maybe tire pressure, which I checked just yesterday (added a little air). Prius drivers get a little spoiled in the MPG's they can get, so it is hard to believe getting 42 or 43 mpg's is bad ;)
     
  6. andyprius

    andyprius Senior Member

    Joined:
    Feb 21, 2005
    2,212
    164
    0
    Location:
    Sacramento, California.
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    ONE low tire can make a big difference.
     
  7. patbrady

    patbrady New Member

    Joined:
    Sep 18, 2010
    1
    0
    0
    Location:
    cascade
    Vehicle:
    2008 Prius
    Model:
    N/A
    Can only say as I previously posted my 2008 went from 51.3 to barely 40.1 after an oil change (reg) and new Cooper Radial tires G54 Touring High Mileage 185/65 R15 I paid $ 440 for these tires I have put on 3,000 miles and still can only get 40. miles per gallon I use 87 grade fuel.
     
  8. narf

    narf Active Member

    Joined:
    Mar 15, 2005
    598
    29
    4
    Location:
    Colorado
    Vehicle:
    2016 Prius
    Model:
    Four Touring
    Overfilling the oil can make a BIG difference. If the oil is above the top mark on the dipstick it can end up getting frothed up by the bottom of the crank (I have been told), and MPG will drop. I always change the oil myself and find 3 quarts is enough to bring the oil up to the midpoint between low and high. 4 quarts is too much.

    My 2008 Touring has 31000 miles on it and it's getting about 53 mpg on the current tank.
     
  9. jyourich

    jyourich Junior Member

    Joined:
    Nov 24, 2008
    2
    0
    0
    Location:
    Boswell, PA
    Vehicle:
    2013 Prius
    Model:
    N/A
    Hello mmnepps. Have experienced the exact same thing. Everything said in the rest of the thread is conducive of low mpg. By 36000 miles I experienced an inverter meltdown and Toyota replaced it under warranty. Everything is back to my normal. I live in Pa Laurel Highlands at get 49 mpg. Run Hankook Mileage Plus II p185/65r15 (lrr) inflated to 36psi, still good ride, and discipline myself to drive as stealthy as possibly. It only takes a few miles of not paying attention to loose mpg. When I travel east or west off the mountain I'm in the mid 50's. Good fuel, lower oil level, higher tire pressure, locale, clean air filters, a good wax job and paying attention help increase mpg.
     
  10. Hal W

    Hal W New Member

    Joined:
    Sep 26, 2010
    872
    52
    0
    Location:
    Grand Forks,B.C. Canada
    Vehicle:
    2006 Prius
    Model:
    II
    New tires can drop your MPG. Have you checked the wheel alignment? Also check the wheel bearings.Dirty air cleaner. H
     
  11. Lindon

    Lindon New Member

    Joined:
    Oct 8, 2007
    21
    0
    0
    Last June the mpg in our 2008 dropped from 52 to 42 mpg. The only thing that changed was new tires were installed. Toyota didn't think that was the major culprit, they blamed it on the Summer gas blend. This week the mpg has increased to 52 again. I use ethanol free gas (confirmed by H2O test), so that hasn't been a variable. If it were new tire break in, I'd think it would be a gradual improvement. With winter gas back at the pumps, I think the gasoline blend is the major factor that impacted our mpg reduction. However, one thing that refutes this is, summer blend should improve mpg, because theoretically it has more energy. Now the question is how long will this continue?
     
  12. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    4,059
    959
    0
    Location:
    Australia
    Vehicle:
    2005 Prius
    That's interesting Lindon, the way your MPG's both declined and then returned so suddenly. The only thing about the "summer gas" theory is that I'd expect a lot of other people here would have noticed the same effect.

    Has there been a significant drop in temperature over this last week that your MPG's has improved? If so then perhaps there's something compromised in the cooling of you're vehicle (eg maybe HV battery maybe inverter maybe something else) that is marginal but not quite bad enough to trigger codes?

    Let us know if the improved MPG remains over several tank fulls. It's an interesting puzzle.
     
Loading...