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Fuel Consumption - Idling after Start

Discussion in 'Gen 2 Prius Technical Discussion' started by Fibb222, Oct 26, 2006.

  1. Fibb222

    Fibb222 New Member

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    Hi Everyone, I just bought a used 2004 Prius and I have some questions:

    I searched high and low for an answer to this one but couldn't find any answers.


    My question is: why, soon after I power up, does the consumption screen show a full 10L/100km of gas consumption (the maximum on a Canadian Prius) when the car is stopped and the engine is just idling?

    I know that when I first turn the car on the engine comes on to heat up the catalytic converter, possibly charge the main battery and what not. I'm fine with that.

    What I don't get is why the consumption bar is so high when the engine is just at idle. The engine doesn't sound like it is running at high rpms or anything.

    Anybody know for sure if this is fine or normal?

    Also, I have experienced some engine shudder at shutdown and also some minor shaking during idle just after starting. The former I've read is common, the latter one has me a little concerned. But wouldn't I get some kind of "service engine" light if there was a problem?

    Overall I'm getting decent mileage on my first tank. 5.3 L/100km after 200 km. It's not exactly warm outside (<15C) and I've been making a lot of short trips so I'm ok with this overall consumption.

    Thanks
     
    #1 Fibb222, Oct 26, 2006
  2. AAWADKE

    AAWADKE New Member

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    <div class='quotetop'>QUOTE(Fibb222 @ Oct 26 2006, 01:17 PM) [snapback]338725[/snapback]</div>
    Its simple !!!
    If your engine is idling, you are not moving (that is stand-still) and which means u r not going anywhere ....and also ur wheels not rotating. Your car is burning gas but not travelling any miles.....go figure why the comsumption would be that high..
     
    #2 AAWADKE, Oct 26, 2006
  3. eagle33199

    eagle33199 Platinum Member

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    It sounds pretty much normal to me.

    While the engine may not be at high RPM's, if you aren't moving, then any gas usage will put you at infinite L/km - the top may be small, but the bottom number is 0, giving you infinite.

    When the engine is really cold and I've just started it up, just sitting there it may shake a little bit. It's not really anything to worry about - when you're moving, it shouldn't be shaking.
     
    #3 eagle33199, Oct 26, 2006
  4. Beryl Octet

    Beryl Octet New Member

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    <div class='quotetop'>QUOTE(Fibb222 @ Oct 26 2006, 02:17 PM) [snapback]338725[/snapback]</div>
    It's normal, if a bit surprising. With cold weather (37F the other morning), I noticed that the gas engine kept running at a stoplight where normally it would have shut off. This happens to keep the heat up. I see 0 mpg, though, and I'd have thought the liters/kilometer display would have resulted in a DIV_BY_ZERO error message and a big stack trace printout. That's a joke, btw, enjoy the Prius.
     
    #4 Beryl Octet, Oct 26, 2006
  5. Tideland Prius

    Tideland Prius Moderator of the North
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    <div class='quotetop'>QUOTE(Fibb222 @ Oct 26 2006, 11:17 AM) [snapback]338725[/snapback]</div>
    That's fine. The only time I don't get a full bar in the first 5 mins is if the engine's warmed up. Then I'm around 7.5L/100km for the first bar. Think about it for a moment. If you're idling and you're not moving or moving at a slow pace, if you were to do that for 100kms, the computer shows you how much fuel you would've used. Well, 10L/100km is the max but you get the gist.

    It is cold enough that if the engine isn't warmed, there will be shudder at shutdown. Mine's already starting to do that and it's 10°C (12°C now) outside across the strait.

    Also, if the engine is sorta warm but not warm enough to shut down (or if you're demanding heat soon after you started), it will feel like the engine is undecisive - as if it wants to shut down but it can't so you feel this rough idle. Next time you feel that, turn off the climate control. The engine should shut off.

    5.3L/100km is pretty good for Victoria city driving. Keep at it and you'll match the rest of us. I'm at 4.4L/100km but that's because I've been avoiding the hill that I have to climb to get to downtown lol.
     
    #5 Tideland Prius, Oct 26, 2006
  6. eagle33199

    eagle33199 Platinum Member

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    As an addition to what i said earlier, think of how we have it in MPG...

    You're stopped and the engine is running: 0MPG
    You're stopped and the engine isn't running: 0MPG

    They represent two completely different mileage scenarios, and yet have the same result on the screen!
     
    #6 eagle33199, Oct 26, 2006
  7. David Beale

    David Beale Senior Member

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    Be happy. The Scangauge tells the truth - 9999 l/100 km. I ignore it. Heck, I'm driving a SUV, I have a licence to burn gas!
     
    #7 David Beale, Oct 26, 2006
  8. Fibb222

    Fibb222 New Member

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    <div class='quotetop'>QUOTE(David Beale @ Oct 26 2006, 12:48 PM) [snapback]338814[/snapback]</div>
    Well I'm really glad to see that everyone who responded "said" not to worry about these things. Thanks for all your replies.

    Some of the answers bring up another interesting thought. I understand that if the distance travelled is zero and if I'm consuming any gas at all the calculation results in a very big number as zero is on the denominator.

    However, am I correct in assuming that if the car was warm and I drove steadily for 2.5 minutes consuming 5.0 L/100km the whole time and then stopped for 2.5 minutes with the ICE off, that the 5 minute average bar would read out 5.0 L/100km? i.e. in its calculation, the MFD computer only uses the time when the engine is running, in this case, the first 2.5 minutes.

    In a similar scenario where everything else is the same but the ICE idled for the last minute would the 5 min average be higher than 5.0 L/100km. i.e. the computer would take into account the gas consumed at idle.

    I haven't tried the real world experiment yet.

    Exactly the same for me too.

     
    #8 Fibb222, Oct 26, 2006
  9. Frank Hudon

    Frank Hudon Senior Member

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    not necessaraily turn the heat off, I normally set it at around 20C and not on Auto. I select the outlets as required and I don't run the defroster if possible as that starts the A/C a real milage killer as well. The ruff shut down is pretty normal in cold weather as has been said and even more if the wrong weight oil has been put in the ICE. Lots of places still persist in using 10/30 instead of 5/30 and on a cold or cool engine the camshaft oil control controller can't dump that as fast as it should and it takes a while for the cam to retard to let the compression ratio drop to 9 to 1. and that causes the shaking as the crank sensor and the cam sensor fight with the computer for control and shut down.
     
    #9 Frank Hudon, Oct 26, 2006
  10. theorist

    theorist Member

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    Does anyone remember the choke on old cars? It's not entirely gone, it's automatic. A cold engine uses a richer fuel-air mix to warm up the engine and more importantly the catalytic converter quickly. A cold engine is less thermodynamically efficient and wears faster. A cold catalytic converter doesn't reduce polutants effectively. The engine in essentially burning extra fuel to warm up the engine and catalytic converter. Instead of calling it choke, they refer to open loop.

    The 0 mpg or infinite L/100km is always true if speed (or distance) is zero. The lower thermodynamic efficiency is still true with cold engines and really cold ambient temperatures. The open loop sounds like a key factor since you were asking why the consumption is so high soon after starting a cold engine.
     
    #10 theorist, Oct 26, 2006
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