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Cold weather driving observation

Discussion in 'Gen 2 Prius Technical Discussion' started by gazz, Sep 18, 2007.

  1. gazz

    gazz Member

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    The last few days its been getting colder in the mornings, down to 5C this morning. What I have been trying to do is understand what would/is pulling the mpg down. This morning I put my EBH on for 3 hrs so it got the engine over 40C (past stage 1) the car did not go through the 60sec warm up it and would glide straight away (this did surprise me). So instead of a warm up down my street to the main road I glided 50% of the way. So I assumed I would get a good first 5 mins which was OK about a good normal, but my main observation was that during the glide stages of my journey all was well and got a few 100mpg as normal, but in the stages where I would normally get between 60-70 UK mpg it was down to 50 - 60. As this was my normal route to work it is very predictable.

    So to sum up what I thought would be the problem in the cold was the first 5 mins was actually the normal warmed up driving, any ideas what would pull the normal warm driving down. by the way I used the heater sparingly.

    Another point I noticed was that the intake temperature was 16C at startup and very slowly over the first 5 mins dropped to about 9C which is about 4C above ambient. I was surprised how warm the intake temp was and how long it stayed above ambient. Could it be as simple as could intake air? (I have my upper grills blocked)

    Thanks

    Gary
     
    #1 gazz, Sep 18, 2007
  2. efusco

    efusco Moderator Emeritus
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    Cold battery is the main culprit. That and the cold air circulating through the engine compartment...many of us use grill blocker (pipe insulation is cheap and easy) to reduce the cold air circulation and help hold the heat in the engine compartment.

    Also remember that tire pressure is lower in cold weather and you should check that and air them back up to your desired pressure.

    Finally, even though you can glide early you may get a better pay off by letting the ICE continue to idle during the first minute or so to fully warm all the emissions control stuff, you'll get better performance sooner that way rather than delaying it.

    No answers for the cold battery pack...I've got a few ideas in my head for some low wattage heater blowers that could prewarm it to at least 50-60F.

    *oops, didn't see the "I have my grill blocked part.
     
    #2 efusco, Sep 18, 2007
  3. gazz

    gazz Member

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    <div class='quotetop'>QUOTE(efusco @ Sep 18 2007, 04:31 AM) [snapback]514193[/snapback]</div>
    But what surprised me was that it did not do the 1 min warm up, the ignition angle went straight to +. so as I could glide a bit then had a slight incline which the ICE would have to be on so warmed the engine at that point.

    Even with a warmed block do you think the engine runs rich, if so how can you tell when it is running normal. The reason I ask is that I thought the first 60 secs running negative ignition was when most the enrichment took place to warm the engine.

    Also at what temp would you block more grills?
     
    #3 gazz, Sep 18, 2007
  4. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(gazz @ Sep 18 2007, 05:04 AM) [snapback]514195[/snapback]</div>
    Depending upon how warm the ICE runs at a low rpm and rich until the emissions control system is warm. Best way to tell is that with gentle to moderate throttle the rpm will lock at 1275rpm initially, once through that phase of warm up it'll drop down to 1100 and then begin acting more normally. With a cold battery the demand for the ICE comes sooner and easier since the battery isn't able to provide as much power as usual.



    You could block the upper and lower grills now with those temps. I usually block my upper when the OAT is around 60F consistantly and the lower at 40-50F consistantly. Others do it at higher temps than that without problem, but my driving conditions vary a lot and I don't want to get into trouble with temps.
     
    #4 efusco, Sep 18, 2007
  5. gazz

    gazz Member

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    <div class='quotetop'>QUOTE(efusco @ Sep 18 2007, 05:11 AM) [snapback]514196[/snapback]</div>
    Is it worth ensuring the battery is at a good SOC when you park up. I can EV the last half mile easily, but it pulls down the SOC 1 bar so the next morning it is about 3-4 bars. I could use the ICE or even force a bit more charge to ensure the next day the SOC is high, what do you think?

    Also I posted the other day about taking intake air from behind the rad rather than the side of the engine bay, have you any thoughts on that? or in the could will the rad give of no heat at all. I might hook up a temp sensor to find any warm spots under the hood.
     
    #5 gazz, Sep 18, 2007
  6. FireEngineer

    FireEngineer Active Member

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    Try not gliding to the main street. Try Evans suggestion of letting the engine carry you at 1275-1280RPM until you see your engine temp will give you stage 4.

    Wayne
     
    #6 FireEngineer, Sep 18, 2007
  7. gazz

    gazz Member

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    <div class='quotetop'>QUOTE(FireEngineer @ Sep 18 2007, 10:21 AM) [snapback]514288[/snapback]</div>
    Thanks Wayne,

    What I am trying to do is understand what pulls your winter mpg down, as I said this morning I got the engine upto 40C (stage2) with the EBH, so the first 5 minute mpg was just like a hot day or a day warm day with a little EBHeating. The problem was that for the next 30 minutes of driving the mpg was slightly down on a warm day, especially when you could not do a lot of gliding. The point is, is that the engine was a full temp most of the time, conditions were good so what pulled the mpg down, is it just the cold air on the intake. (I will double check TP)

    I suppose where I am at is that I am happy I understand warm driving and how conditions effect my mpg (wind, rain, stages etc) I am trying to understand cold driving (temp, EBH, heater use) gives me something to done on my way to work each day, and saves me a lot of money.

    Thanks
    Gary
     
    #7 gazz, Sep 18, 2007
  8. David Beale

    David Beale Senior Member

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    It isn't just the low engine temp that forces the engine to run. In fact, in my car the cat. temp seems to be the first controlling factor, -then- the engine temp. My car seems to wait to "see" if the engine temp can be brought up in "normal running", whereas it doesn't wait to warm the cat.
    As an example, I back out of my garage. Engine starts to warm the cat. After about 30 sec to a min. engine shuts off, even though the coolant temp is not fully up. This is "fixed" later as I move away and need the engine power, so the car gets two jobs done at once - the extra needed power and the extra heat in the coolant.
     
    #8 David Beale, Sep 18, 2007
  9. gazz

    gazz Member

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    <div class='quotetop'>QUOTE(David Beale @ Sep 18 2007, 11:20 AM) [snapback]514320[/snapback]</div>
    Thanks

    Thats what I though but this morning the EBH got the start temperature to over 40C and it did not do the 30-60 second engine run. This is the first time I have got the engine that warm with the EBH. I will try again tomorrow to make shaw I am not mistaken.

    Gary
     
    #9 gazz, Sep 18, 2007
  10. jayman

    jayman Senior Member

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    Gary

    Are you parking outside or in an enclosed and insulated garage? Once it gets cooler, the grease in the wheel bearings, the WS fluid in the transaxle, the motor oil, etc all become a bit more viscous. That extra drag until things warm up will impact your fuel economy.

    At an extreme, say at -40, conventional oils become so viscous that instead of flowing, they turn semi-solid. The WS fluid appears to be a thin synthetic fluid, but most motor oils are too thick for cold temps, especially initial startup. A regular 5W-30 only has to be "good" to -30 C to meet the SAE cold pumping specs. I run a synthetic 0W-20 for winter

    Although I just sold my condo, I have heated underground parking. Even at -40, the first block or so the car behaved just like summer. Then as the car cooled off, the fuel economy slowly but surely declined. At -40 I usually average around 7.5 l/100km in stop-and-inch city driving.

    Just to keep the entire vehicle warm, I found a replacement house with a well insulated and heated garage. I'm too old and too miserable to scrape ice off windows and freeze my pointy bits off.

    jay
     
    #10 jayman, Sep 18, 2007
  11. FireEngineer

    FireEngineer Active Member

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    <div class='quotetop'>QUOTE(jayman @ Sep 18 2007, 12:41 PM) [snapback]514374[/snapback]</div>
    Also your tires will start to increase their rolling resistance when the temp goes below 15C, and it is progressive to some lower point depending on the tire. since you said you were at 5C that could be a part of it. The numerous posts to "overfill" the tire pressure will help to counter this to some effect. And since you lose 1 PSI for every 10F you need to keep after it. I can tell with my route when I have lost as little as 3 PSI.

    Wayne
     
    #11 FireEngineer, Sep 18, 2007
  12. gazz

    gazz Member

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    <div class='quotetop'>QUOTE(FireEngineer @ Sep 18 2007, 12:53 PM) [snapback]514381[/snapback]</div>
    Thanks I will check tire pressure.
     
    #12 gazz, Sep 18, 2007
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