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Sudden MPG Dropoff - What Should I look For?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by KJ Fitz, Apr 21, 2017.

  1. KJ Fitz

    KJ Fitz Junior Member

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    Awhile back I bought myself a Gen 3 and gave the 2008 to my Son. (With Mama's V we are a three Prii family). For awhile he was getting similar mileage to what I did in it -- high 40s to occasionally 50 MPG. When I went to fill it up on the Navy Base ($1/gallon cheaper than downtown here on Guam) I noticed it was down to the upper 30s.

    I'm going to pick up an OBDII scanner tonight. Anything in particular I should be looking for?

    The car has only 110,000 miles, all on Guam, no cold weather, average 12 mile commute at about 45 MPH. Spark plugs and transmission oil were recently changed and I always run fresh synthetic oil. Recently (within a year) installed a new Yellowtop 12v battery.

    Thoughts?

    Also looking at the Prolong Grid Charger just in case the traction battery is getting worn, has anyone had any good/bad/indifferent experiences with it? I'd sure rather buy that for $349 than a battery for $4000 (we're a Lo-o-o-ng way from a reconditioner service).

    Thanks,

    Kelly
     
    #1 KJ Fitz, Apr 21, 2017
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  2. fuzzy1

    fuzzy1 Senior Member

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    #2 fuzzy1, Apr 21, 2017
  3. KJ Fitz

    KJ Fitz Junior Member

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    #3 KJ Fitz, Apr 21, 2017
  4. KJ Fitz

    KJ Fitz Junior Member

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    Ah, there's a thought -- and a relatively low budget solution if that's the case.

    I assume the easiest troubleshoot is to jack it up and see if wheels turn freely, right?

    And thank you for the idea.
     
    #4 KJ Fitz, Apr 21, 2017
  5. fuzzy1

    fuzzy1 Senior Member

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    For the rears, yes.

    For the fronts, tied to the propulsion system, not as straightforward. But since the Park lock is on the transaxle side of the differential, this still ought to work when both fronts are up at the same time. Note that both front wheels are constrained to turn at the same time and same speed, though in opposite directions, and with greater system drag and inertia.
     
    #5 fuzzy1, Apr 21, 2017
  6. valde3

    valde3 Senior Member

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    With bough front wheels of the ground you can tell which side the bare drag is on. If you turn the wheel back and forth you will notice that there is a small area of free movement before you start turning the other wheel. If there isn’t that free area in one side that side has dragging brake.
     
    #6 valde3, Apr 21, 2017
  7. andrewclaus

    andrewclaus Active Member

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    You can also check the temperature of the hubs. It's safe and easy if you can use a non-contact infrared gun (I got one from Amazon for under $20). Otherwise be very careful if you use touch. Try spritzing some water first, and smell for smoke. It's also best if you can do this test with very minimal use of the service brakes. Use B mode to slow down, and head up a hill to come to a stop.

    If you do find a hot hub under those conditions, you'll probably want to flush the brake fluid after the brake repair.
     
    #7 andrewclaus, Apr 21, 2017
  8. KJ Fitz

    KJ Fitz Junior Member

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    #8 KJ Fitz, Apr 21, 2017
  9. edthefox5

    edthefox5 Senior Member

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    My thoughts are it's a 9 year old car and has 110000 miles so time for some maintenance.
    Trans fluid and especially inverter coolant and engine coolant. And must replace the water pump belt.
    Lose that belt and car overheats and you'll never know till the check engine light comes on
    By then too late engine damage. Bad design.

    Check tire pressure and baseline test the car to see if it really has an issue. Find nice long 4 mile flat road no traffic.Get up to 60 mph and set cruise control and then reset the mileage meter on the mfd the one that zeros out when u get gas. After the 4 miles read mpg on mfd. should read at least 58 mpgs.
     
    #9 edthefox5, Apr 21, 2017
  10. KJ Fitz

    KJ Fitz Junior Member

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    Thanks, Ed,

    Changed inverter coolant, trans oil, spark plugs and drive belt at 100K. Engine coolant has not been changed, good idea. Will check pressures and baseline today, and check for any fault codes.

    When I checked yesterday his average mpg was showing 39.5 on this tank. Seems low. Will try your suggested check.
     
    #10 KJ Fitz, Apr 21, 2017
  11. KJ Fitz

    KJ Fitz Junior Member

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    Interesting. Ordered an IR gun a moment ago, might have interesting applications in my science classes, too!


     
    #11 KJ Fitz, Apr 21, 2017
  12. andrewclaus

    andrewclaus Active Member

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    I use mine in the kitchen, for the wood stove, to check accuracy of room thermostats and outdoor thermometers, for checking building insulation/caulking, for working on furnaces and boilers, in addition to the car.
     
    #12 andrewclaus, Apr 21, 2017
  13. Mendel Leisk

    Mendel Leisk Senior Member

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    You should be able to get away with a quick touch on the rims, even if they're getting very hot. Just hold you hand close first, if you're concerned.
     
    #13 Mendel Leisk, Apr 21, 2017
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  14. edthefox5

    edthefox5 Senior Member

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    If the disc brakes are dragging so much the rims are hot you will easily smell it in the car if recirc is turned off. Dragging brakes get the hubs and the rims super freakin' hot really fast. Major cause of the car on fire on the side of the road. Tire catches fire and car goes up.

    Plus you will instantly feel it in the steering it pulls the car to one side. Even the slightest drag on one side will pull the steering.
    I know its happened to me.
     
    #14 edthefox5, Apr 21, 2017
  15. KJ Fitz

    KJ Fitz Junior Member

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    Lesson one, check the easy stuff first.

    After digging out maintenance records to confirm that inverter coolant, engine coolant and drive belt were new, buying an OBDii scanner (no codes thrown), and checking for dragging brakes (also negative), I FINALLY bought him a proper tire gauge. All four were 8-10 psi low (he'd been relying on the gauge on the pump at the gas station).

    Correctly inflated the tires, replaced the engine air filter, and voila, back up into the high 40s!
     
    #15 KJ Fitz, Apr 22, 2017
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  16. KJ Fitz

    KJ Fitz Junior Member

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    On the other hand, I DID get a new tool out of the whole thing (grin)!
     
    #16 KJ Fitz, Apr 22, 2017
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