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Odd fuel usage

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Kaminski, Jul 25, 2014.

  1. Kaminski

    Kaminski New Member

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    Hey guys,

    New Irish member here.
    I recently picked up a low milage 06 gen 2. Got it with 59k miles on the clock.
    So far so good with it, except for one issue.

    It seems when the car is hot, and a full/almost full battery, sometimes the engine keeps running.
    The L per 100km will only drop to 1.8-2 L per 100km, but the engine monitor shows no output from the engine. I can feel/here the engine running. If i hit the EV button the engine does stop, and will start back up when released.
    While this is happning the fuel usage seems to be X higher, like the baseline is now 2. so doing 30mph can read 5-13 L per 100km which is more than what it uses at 70mph!.

    The dealer where i got it is just saying if its not giving a warning light its ok, but im sure this isnt normal. It wasnt the case for the first 2.5k miles anyway.

    The MPG dosnt seem to be affected too much, Im getting between 65-69mpg from motorway driving. Im sure without this issue it might be a bit more though.

    Has anyone got any ideas what might be causing this?

    Cheers :)
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The reason the engine is running is because MG1 is spinning the engine to use up excess traction battery charge. This is normal. No fuel is being used to spin the engine, just electric power from the traction battery.

    I assume you are quoting mileage using Imperial gallons. That is quite good fuel economy. I don't believe your car has any power train issues.
     
  3. Kaminski

    Kaminski New Member

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    yeah imperial (uk ) mpg.
    Ah ok, well that makes some sence alright!
    So the excess reading when driving is almost false then, say when its reading say 5+ when using some engine at 30mph?
    Id have thought at worst it would be a sensor anyway. One owner car before me, bought from and services in the same dealer i bought it from.
     
  4. The Electric Me

    The Electric Me Go Speed Go!

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    Ah...the ways of the Hybrid Synergy Drive can be mysterious indeed....

    I guess my gut reaction is, that if you are averaging 65-69 mpg? Then everything is great.

    It is however hard to evaluate.

    You say two things. One that you "recently" obtained the vehicle, two that you are "sure" it's behavior isn't normal.

    Have you owned a Prius/Hybrid before? If not? How can you be sure it's not "normal"?

    Some new owners I think have expectations concerning MPG and efficiency, then can be surprised when they notice something like the engine running when they think it shouldn't. But people forget that in some ways it's a pretty complicated system, designed to do MORE than just return great gas mileage.

    My observation, is that The Prius makes operational decisions in regards to a whole bunch of criteria. Some not intuitive to the person behind the wheel at any given moment. But the system considers battery charge, exhaust, and efficiency.

    It's a bit of a cop out on my behalf. But I generally don't try to out think the system. There are some times when I'm driving my Prius, and I notice that "I" think the engine is warmed up, the battery charged and I'm driving slow enough, but the engine is running. But instead of worrying about the fact that for that particular moment "I" think I should be afforded full EV driving? I evaluate my Prius's performance instead in a bigger picture. That is how is my gas mileage and efficiency from fill up to fill up.

    As long as my mileage is good, and relatively consistent (outside of seasonal ups and downs). Then my approach is NOT to worry about any specific moments that I think, I know how my Prius should be running. Because? I'm probably not as smart as my Prius.

    I would caveat my own opinion by saying, that is NOT to say you don't possibly have a problem. I would suspect if you do? Eventually it would manifest in undeniable ways, with a plummeting of gas mileage or indeed the the fabled warning light and/or codes.

    But for now? If your gas mileage is good, and relatively consistent from fill up to fill up, I wouldn't worry.
     
  5. Kaminski

    Kaminski New Member

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    Thanks both of you for super answers.
    As you said, not had the car all that long, and its the first Hybrid ive had.

    It was more the fact that sometimes it wont use the battery, when theres full charge and other times it will at the same speeds/roads.
    But as you said, the car is smarter than me (and thats not hard :p) and it is getting good mpg.

    All and all i really like the car. After driving stiff riding sports car for the last 7 years, this is a nice change, although I do miss the power. But with driving 86miles a day the last car was burning though way too much fuel.
     
  6. dolj

    dolj Senior Member

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    Hi and welcome to PC.
    Hard to know what you mean by "the car is hot" in that do mean you have been driving for 5 mins or half and hour? When this happens, it is possible that you have been driving for less than 10 mins? If so, the HSD is not fully warmed up.

    I have noticed that the Prius can exhibit the behaviour you described if it has not reached Stage 4 in the warm up cycle. Have a read of the article I have linked to in my signature of the 5 stages of warm up. You need to come to a full stop and wait for about 6-12 seconds for the engine to do it little calibration sequence and once this happens you will be in stage 4. Once in Stage 4, the engine will switch off completely more often.

    Let us know if you don't feel that is the issue.

    What Patrick mentioned will only happen if the battery is fully charged at it's maximum capacity and showing 8 bars.

    I also second the tenet of what The Electric Me said:
    • Don't try and second guess the HSD nor worry too much about what it is doing;
    • Do try to look at the bigger picture of consumption/fuel economy. If you're averaging 4.8-4.6 l/100km (or better) then you're doing ok. Using a web logging site (such as fuelly.com e. g.) is useful to keep a track of your consumption and provide historical stats.
    Most of all, enjoy the car.

    Cheers.
     
    #6 dolj, Jul 25, 2014
    Last edited: Jul 25, 2014
  7. Kaminski

    Kaminski New Member

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    Nice wrightup on the stages Dolj, good to know.
    What i mean by hot, is driving for ~40min motorway speeds, so I would say Id be in stage 5.
    Say coming off an offramp, dropping down to 20-30mph the car will show its running only on battery but using 2ish L per 100km. applying any more than a feather touch on the throttle will bring the engine in, and show a fuel usage of 5-20 L per 100Km. It seems like the engine is running harder while this is happing. This could well be just in my head though.
    The only real reason i question this is it dosnt do it all the time at say the same points in the road, and seems to be more common in the last few weeks than before. Even sitting still in traffic sometimes it will read 1.8-2.2ish L .

    I am very good at over thinking things, and been a slight be paranoid! I am enjoying the car though. There really nice to drive, the auto box isnt as bad as I was led to believe, just takes a little getting used too.

    Oh the avrage the computer is reading is 4.2L per 100Km, so in that sence its running awesome!
    Best ive got working out the fuel manully was 1001Km on 42L motorway driving, 4.1ish L per 100Km. :)
     
  8. dolj

    dolj Senior Member

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    Hmmm, 20 l/100km is pretty high in this circumstance.

    It is possible to drive for 40 mins and be stuck in stage 3b, especially if you get on the motorway fairly soon after startup. You still need to come to a complete halt and wait till the ICE shuts down 6-12 sec later. If you are running for less than 5 mins and the ICE does not shut down with in 6-12 sec, check to see if the A/C in on. Shut it off if it is and the ICE should then shut down. You can turn it back on straight after and get going again. Note it is possible the drop out of stage 4 back to stage 3b during a journey, so don't be surprised if you have to do the stopping thing more than once.

    One thing you will notice and is normal, is that there sometime appears to be no rhyme or reason to what the HSD does. I can definitely vouch for the observation that the HSD does different things at different times on the same drive.

    4.1 l/100 km is pretty awesome! Certainly something to be proud of. If you can average that consistently then I'd say you are doing a lot of things right. Keep it up. :)

    hope this helps.
     
  9. Kaminski

    Kaminski New Member

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    Cheers for all the replys :) You lot have settled my mind a good bit.
    Also I got a years parts and labour from the Toyota dealer on it, so im not too worried about things going wrong.

    Nice to see a friendly fourm. So many out there are so up there own a$$'s :)

    It seems like I figured out the warp stealth my my self :) have done legs of the trip behind trucks (not too close dont worry) running on ev only at 50mph :)