My 2006 starts in phase 1b in cold weather

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by nerfer, Jan 20, 2011.

  1. nerfer

    nerfer A young senior member

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    Whenever the temperature is below freezing, the coolant doesn't seem to get pumped out of the thermos. I had the problem with the pump squealing in cold weather, so I had it fixed (mentioned the TSB to the Toyota guy), so it no longer squeals, but it seems it doesn't even run in cold weather. The engine typically starts up within a few seconds, not the usual 7 seconds delay, so it appears it isn't even trying to do this.

    What's more, I've noticed with the Scangauge that it's not accelerating on battery-only in the first several seconds of driving, so it's apparently skipping all of stage 1a. The engine runs a bit rough until the coolant gets up to about 70'F or so. I have a short commute, but even on longer drives I haven't noticed the engine temperature getting too high, so apparently there's still some coolant in the system, maybe the rest gets pumped in when things warm up enough? Or maybe it doesn't get pumped into the thermos in the first place, I'll try to pay more attention the next time I turn my car off after driving to work. But I know when I park in the garage at home the coolant pump runs after I turn the car off, so I believe it's always working on the end of the trip.

    Anything I should check? Temperatures above freezing are no problem, the coolant itself is okay I think. I want to be prepared if and when I talk to the dealer, when I told them about the coolant pump making too much noise the service guy was surprised I could tell that and knew what it was, I think he was questioning my judgment a bit. If I go in and tell them my car starts up immediately in stage 1b, they'll probably have no idea what I'm talking about.
     
  2. 2009Prius

    2009Prius A Wimpy DIYer

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    Not sure about the warm up stage skipping but I think Prius is pretty smart about deciding whether to transfer coolant between the thermos and the engine cooling loop depending on the coolant temperature measured at various places - in order to optimize fuel efficiency. Maybe your driving pattern is such that when it's below freezing the temperature distribution of the coolant just happens to make the transfer unnecessary.

    Here are two examples recorded during two separate trips with an identical initial outside air temperature of 28.4 F (below freezing) - my Prius decided to do the transfer in one but not the other:
    [​IMG]

    [​IMG]

    Hope this helps. :)
     
  3. nerfer

    nerfer A young senior member

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    This is news to me - you're saying it purposefully doesn't always transfer the coolant at startup? How do you measure the water temperature separately from the engine temperature? It looks like in your first chart that the coolant temperature was in the 140's but didn't get circulated past your sensor until the 7 seconds had elapsed and the engine kicked on.

    I estimated the change in behavior to be at freezing, that tended to be the case, but I know it did transfer at least once at 28'F. I only pay attention about half the time anyway. I have a short commute, so I can see where the coolant doesn't get very warm, even though I block the grill and have an EBH installed (can only plug in at home, not at work).
     
  4. 2009Prius

    2009Prius A Wimpy DIYer

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    Yes you can imagine (in the extreme case) if the coolant in the thermos is colder than that in the engine loop then there is no point of doing the transfer at startup.
    The temperatures are available at the OBDII connector below the driver side dash. See my PriiDash(TM) project for more details. I don't known where exactly the sensors are but they agree well with the engine coolant T reported by standard OBD requests using ScanGaugeII.
    I think the sharp rise in coolant temperature corresponds to the transfer of hot coolant from the thermos into the engine cooling loop sometime before the engine starts. Once the engine starts the temperature actually drops, presumably due to mixing with cold coolant from other part of the loop since the water pump is driven by the engine.
    Looks like you have done all you can to help improving the fuel efficiency giving your short commute. Good luck! :)
     
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