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If your mileage is dropping you might need a long drive.

Discussion in 'Gen 3 Prius Fuel Economy' started by ALS, Oct 4, 2020.

  1. ALS

    ALS Active Member

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    I know many of us complain about the fuel mileage dropping as the miles increase but has your driving become more urban than highway?

    Scotty Kilmer (YouTube) had a video up a little while ago where he explained the need for an Italian Tune-up. Not where you floor it to blow the carbon out of the cylinders, but the need every few months to take a few hour trip at normal highway speeds to get the same results.

    I've known this for years with my Volvo 960. If I take short trips under say an hour over time my gas mileage suffers. 28.5 mpg highway will drop into the 24's over a period of time. Yet take it on a four of five hour run each way and the fuel mileage will pop right back up into the 28's after a few hours on the road.

    I finally got around to making a trip with the 2010 Prius 93,400 miles today. My fuel mileage has been abysmal to say the least. It's been impossible even at 55 mph to break 49 mpg on the highway. I filled up at the start and reset the trip meter and calibrated my Scan Gauge. Today I made a run for three hours west into Ohio topped off the gas tank and returned back home. My trip over 49.2 miles per gallon at normal highway speeds of 55-65 miles per hour. On my return trip my fuel mileage had gone up to 56.5 miles per gallon by the time I got home. A 14.84% increase is something to be happy about.

    It's a cheap way to figure out is your fuel mileage dropping because the car isn't seeing enough highway time to get everything nice and hot and fuel system flowing correctly for actual results. Or is your fuel mileage dropping because of a physical problem that needs to be addressed?

    The reason I did this run today was the Dealer keeps telling me I need to replace the spark plugs. The car has been running fine except for the declining fuel mileage. I was starting to wonder if it was the plugs, I got my answer today NOPE.
     
  2. bisco

    bisco cookie crumbler

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    italian tune up
     
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  3. cnc97

    cnc97 Senior Member

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    What are your coolant temps during your urban drive cycle? If the answer is less then 170 degrees, the thermostat is robbing you of economy as well. It’s either stuck open, or opening too quickly. I say this because I was recently in the same boat as you, highway driving was average to above the averages reported here. However, in town mileage was suffering. I replaced the t-stat, and I was back in the mid forties. My daily commute is around 5 minutes one way.

    I originally bought my car for Uber and other driving jobs, but with the virus, I just do the regular full time job. As long as I’m still saving money over the 16 mpg at best CVPI that I used to drive though, I’m keeping her. Trying to convince the better half that she needs the RAV4 Prime. Maybe sometime down the line I guess.
     
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  4. ALS

    ALS Active Member

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    Thanks, I'll have to pay attention to my H2O temps when driving around town. I'm making trips like you in the 4-5 mile range and I can never get more than into the mid thirties. At least it's a cheap fix if my thermostat is bad.
     
  5. Grit

    Grit Senior Member

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    True. The longer you drive, the better chance ICE can get up to optimal temps. I have grocery runs within miles of each other so I hold peddle down to keep ice on longer to reach at least 152 F to the first store then drive however I want from there yielding 50-60 mpg for in town driving.
     
  6. cnc97

    cnc97 Senior Member

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    I used the 170 degree number from my own travels. The actual advertised t-stat temp is 180. So the closer the vehicle gets to that temp, the happier the car is going to be. Thats only going to get harder to satisfy on my drive as we transition to winter temps. There are alternate routes I can take to make sure the car warms up completely, but that’s almost counter-productive to saving fuel LOL.
     
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  7. Mendel Leisk

    Mendel Leisk Senior Member

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    It'd be nice if if Toyota added a coolant temp gauge, preferably displaying the temp as a number.
     
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  8. Grit

    Grit Senior Member

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    I was thinking of more gauges than That.
     
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  9. NewHybridOwner

    NewHybridOwner Active Member

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    So wouldn't it be advantageous to install a block heater for all-season use anywhere in the world and not just for winter use in the frozen North?
     
  10. Mendel Leisk

    Mendel Leisk Senior Member

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    That's what we do, use ours year round, whenever practical. Two hours preheat is the sweet spot, raised temp to a plateau about 20~30 C above ambient. Often allows garage exit in EV mode.
     
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  11. Grit

    Grit Senior Member

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    You can do the lower grill block (w/ac off) on the terms that you keep an eye on ICE and inverter temps. Mine is blocked when driving in city limits all year long, those drives are always morning so no need to AC up and remove the grill block.
     
  12. ALS

    ALS Active Member

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    My Scan Gauge has water temp setting so that works for me.

    Grit look into a Scan Gauge for your vehicle, plugs into the OBD port.



    It also reads codes and can clear them.
     
  13. PosauneGuy

    PosauneGuy Member

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    Are you sure the 15% increase on the return trip wasn't due to a tailwind?
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    @ALS, sadly my scan gauge, constantly connected, was causing Check Hybrid System warnings and return-to-defaults brake behaviour, had to discontinue use. Yeah just thinking: a $30k car, especially one with geek appeal, should provide basic instrumentation.
     
  15. NewHybridOwner

    NewHybridOwner Active Member

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    But then you have to remember to unblock it for longer trips -- and it only shortens the warm-up time: it doesn't give the engine temperature a head-start.
     
  16. ALS

    ALS Active Member

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    Mendel, knock on wood I've had zero issues with mine.
     
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  17. fotomoto

    fotomoto Senior Member

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    I believe this "bounce-back" in FE numbers phenomenon is simply the elimination of or vast reduction in warmup cycles per tank that long drives produce.
     
  18. ALS

    ALS Active Member

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    @fotomoto what ever it takes to fix a fuel economy problem without throwing money at it.

    @cnc97 I had to make a run to the bank for work and she ran right up to 181 degrees so my thermostat is working correctly.
     
  19. cnc97

    cnc97 Senior Member

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    Mine runs around 193-195. The fan kicks on at 203. Then the fan is back off at 193. But if I recall, it takes 150 degrees to shut off at a stoplight. Someone else who has that info stored will chime in soon enough.
     
  20. Grit

    Grit Senior Member

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    152 F or hotter, EV on mine will kick in on and off on my command.