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What happens to me when the engine is cold.

Discussion in 'Gen III 2010+ Prius Main Forum' started by southjerseycraig, Jan 29, 2010.

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  1. southjerseycraig

    southjerseycraig Member

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    This is what happens to me when I start a cold engine, particularly in cold weather:

    1. The gas mileage when I first start to drive is in the 10s and 20s. I use Trip Meter A to find out what the gas mileage and miles traveled are for each day. So I zero the trip meter when I start the car in the morning. Trip Meter shows very poor gas mileage for the first few minutes.

    2. I have a little trouble accelerating. I make a left turn onto a collector street, and I find the car reluctant to go from, say, 10 to 25 miles per hour. This usually happens only the first time I need to accelerate.

    Are these occurrences normal-- I suspect the first one at least is -- or do I have some kind of problem. I know that these problems occurred in Generation II -- are they issues in Generation III as well? Thanks for your help.
  2. jdcollins5

    jdcollins5 Senior Member

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    1. The first mileage with a cold engine around 10 to 20 mpg is normal to me. I leave in the morning and drive 3 blocks through a residential neighborhood with 25 mph speed limit. My mpg during this time gets up to about 20 to 30 mpg by the time I get to a main thoroughfare.

    2. After the 3 blocks to the thoroughfare, I usually have to accelerate quickly to get up to 45 mph to merge with traffic and then cross over to the left lane. Never a problem accelerating.

    Question, what mode do you usually drive in ECO, NORMAL or POWER? If ECO, this modifies the characteristics of the gas pedal and makes it less sensitive to pedal movement. In other words you have to move the pedal further for intended acceleration. In ECO mode, the car does feel sluggish on acceleration.
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  3. walterm

    walterm Member

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    Both conditions are normal - when the gas engine (ICE) first starts up cold it runs very inefficiently until the exhaust system/catalytic convertor gets heated up. It also relies more on the battery/electric motor to propel the car while the ICE charges the traction battery, so less power is available to propel the car in total until the ICE reaches a better operating temperature.

    There is an old thread detailing the stages of startup operation which has much more detail, perhaps in the Knowledge Base section. There may be a couple of differences from Gen 2 to Gen 3, but overall this should help describe what happens when.

    http://priuschat.com/forums/knowled...perating-mode-availability-reference-aid.html
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  4. qbee42

    qbee42 My other car is a boat

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    Just a minor clarification: Starting with a cold ICE, the Prius adjusts the timing to make heat. Most of the fuel consumed at this point is being burned as if the ICE were a heater. This also heats up the catalytic converter.

    During this warm up period, the Prius tries to avoid drawing power from the ICE. This reluctance to use the ICE is why a cold Prius will feel sluggish.

    The best advice is to drive but take it easy during this short warm up period. The exception comes if you need to pull out into rapid traffic, in which case it makes sense to allow the Prius to briefly warm up before pulling out.

    Tom
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  5. tumbleweed

    tumbleweed Senior Member

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    When you first start the car and it's cold the ICE will start after 15 seconds. For the next 60 seconds it will not supply power to the battery or to drive the wheels, as previously stated. During this time you are running on the battery with the ICE running to heat the catalytic converter, thus the poor mileage. Some very knowledgeable posters have suggested it might be best for mileage if we let the car set and warm up for that minute, I usually just take it really easy so I don't draw the battery down to much.

    If you really need power and put your foot down the engine will supply power to the drive train during that time. You can the bypass the 15 second wait for the ICE to start if you put your foot to the floor (in park) and quickly let up again.
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  6. peirhead

    peirhead Junior Member

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    Our normal daily commute is only 2 km or so, the worst possible scenerio for any car in winter especially....other trips during the week are 5 - 10 km out to the store, stop for a hour or so and 5 - 10 km home...avg speed 30kmph, yet still getting 40 imperial MPG...my son has a Mazda Protege and he gets 24 MPG, and a friend has a sunfire and also is getting around 25 MPG...Prius RULES MPG here!!! the only car that compares is the Jetta diesel.
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  7. David Beale

    David Beale Senior Member

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    I think if you put on the front defroster it also forces the ICE to start sooner. At least that's what I'm seeing in Pearl, a GII.

    I will add my voice to "it's normal". BTW, -any- car will guzzle when cold and will be a little down on power, but for other reasons.
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  8. southjerseycraig

    southjerseycraig Member

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    Thanks to all for your helpful comments. FWIW, I drive in no-mode. When I first got the car, I used ECO, and I found it too hard an adjustment from my previous car, a 1997 Toyota Camry.
  9. Tom183

    Tom183 New Member

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    1) the initial poor mileage isn't just a cold engine - it's also going from 0-25mph (or whatever). Accelleration mpg is always worse than cruising mpg.

    2) seems to be normal - at least, I get the same thing. When you first want to accellerate, there's a bit of hesitation as the ICE is first brought into play. Why is another question - maybe it has to do with that first 60 seconds of warmup... I will test this next trip - start car, wait for ICE to start warm-up, give it 60 seconds, then see if the same hesitation happens. (OT: I also want to see if P&G is possible after that 60-second warm-up, or if the ICE needs more time / higher temps)
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  10. toyolover

    toyolover Member

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    All combustion engines need to warm up in order to burn the fuel efficiently (which in turn produce power). Disel works differently because disel fume explores upon compression. Therefore, extreme cold temperature would be harsher to gasoline engine than the disel. Disel engine lets you feel more "power on the go" quicker than gasoline engine when both are under the same cold temperature. Light up your pedal on the first three minutes to let the engine warm up gradually. Your engine will last a lot longer.
  11. Jim Clark

    Jim Clark Member

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    Sounds normal. All modern ICE powered cars get lower fuel mileage when cold.

    My BMW 330Cic gets terrible average mileage because it's typically only driven on short around town trips. I run 5w-40 oil in it which makes the warm-up even longer.
  12. Tom183

    Tom183 New Member

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    Regarding front defrost and ICE - either the ICE runs the whole time that front defrost is on, or yesterday was so cold (12F) that the front defrost was sucking all the heat away from the engine and it had to keep running to stay warm. Either way, I couldn't pulse&glide with the front defrost on...

    We'll see what happens tonight...
  13. Prius 07

    Prius 07 New Member

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  14. JimN

    JimN Let the games begin!

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    Sounds like you need the block heater. Also block up the grill & while you are out there check & increase your tp. As the others said, situation normal.
  15. chrisj428

    chrisj428 Active Member

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    Craig,

    Funny you should mention this. I am planning on calling the dealer today to discuss this issue...

    I live in a condo with a common parking lot. I'll start the car, reverse out and drive to the end of the lot. When I go to accelerate onto the street, my impression is one of the vehicle hesitating -- almost starved for fuel. This will occur for a good 2-3 seconds before it "clears its throat". From that point forward, the vehicle will drive as normal.

    This only occurs after sitting overnight. In fact, on this occasion, I hadn't driven the vehicle since the afternoon on Saturday and it was particularly recalcitrant this morning. :(
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  16. Tom183

    Tom183 New Member

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    That's exactly what I'm experiencing.

    I tested to see what would happen if I let the ICE idle for a minute first - unfortunately after 1 min it was still idling with no sign of shutting down (12F, so I'm not surprised). There was less hesitation than a cold start, but it was still there.

    Then yesterday I started out without any idling but not stomping too hard on the gas - just a typical strong input (at least halfway, I think) but not pushing harder when it didn't respond - and it felt like ECO/EV mode (even though I was in PWR) until I finally gave in and really put my foot down. So I suspect that the onboard computer knows the ICE is cold and tries to avoid using it until it is warm enough - it will use it if you insist, but tries to avoid it otherwise.

    So today I may try letting the ICE idle until warm enough to shut off (could be a long wait), and see if the same hesitation happens - I don't expect it will. But that will beg another question: is it worth the wait?
  17. qbee42

    qbee42 My other car is a boat

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    As stated before, it depends on whether you have to pull out into fast moving traffic. If you can take it easy, getting in and driving is the best practice. If you have to drive fast, warm it up for a minute.

    Tom
  18. Tom183

    Tom183 New Member

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    Well, yes - if your situation is that simplistic...:rolleyes:

    The question is, is it worth it to wait for the warmup, or just put your foot down? Is there more wear&tear on the engine? Is the FE different? Is either enough to actually matter?
  19. qbee42

    qbee42 My other car is a boat

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    It *is* that simplistic.

    FE is better if you simply drive modestly. If your situation prevents that, a very short warm up will improve FE.

    Engine wear and tear isn't much different either way. The Prius ICE is well taken care of, even during a cold start.

    Is it enough to matter? That all depends on your situation and how picky you are. You could always do a controlled study.

    Tom
  20. chrisj428

    chrisj428 Active Member

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    Tom (qbee42),

    In my case, I'm not trying to accelerate out into fast-moving traffic, nor am I accelerating aggressively. I'm just trying to achieve 25 mph in a residential area at a rate of acceleration somewhat faster than if I were pushing the vehicle myself. Figure just past the midpoint on the HSI screen (the horizon where the ECO leaf goes dark).
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