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High temps dropping fuel economy?

Discussion in 'Gen 3 Prius Fuel Economy' started by MarvHein, Jun 5, 2013.

  1. MarvHein

    MarvHein Junior Member

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    While most of the emphasis I've seen on improving fuel economy seems to focus on warming the car up quickly in cool/cold weather, I seem to be experiencing significant mpg drops at the other end of the spectrum.

    Now that it is nearly 110 in Las Vegas, my Gen3 seems to run the ICE for 10-12 minutes before shutting down. Even at stop signs, it will be running at about 1000 rpm (1200 if the A/C is on). Needless to say, this drops my usual 54 mpg down about 8-10 mpg.

    I am guessing something is hot from sitting in the sun that needs to cool down before it can be used. I have a ScanGauge attached. When I enter the car, the coolant temps are around 130 degrees (engine and inverter) and the drive battery temp is the same.

    Thinking it might be the battery, I attached a shop vac hose from the passenger side dash vent to the battery inlet in the passenger rear and cooled the battery down into the 80's pretty quickly with no difference.

    Somewhere on the trip home, EV mode became available again, but barely. Inverter temps sat around 128-130 the whole time.

    If it's the inverter, any suggestions for cooling it down better than what Toyota has designed? (No, I do not have my grille blocked this time of year!) They must not have temps like this in Japan. ;)
     
    #1 MarvHein, Jun 5, 2013
  2. bisco

    bisco cookie crumbler

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    are you running the a/c full blast and recirc?
     
    #2 bisco, Jun 5, 2013
  3. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    In MS, I find mileage drops once I get into the 90s outside (only 88 today) as I run the A/C to stay cool. I am not interested in how much better my MPG might be in a sauna.
     
    #3 JimboPalmer, Jun 5, 2013
    F8L likes this.
  4. F8L

    F8L Protecting Habitat & AG Lands

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    Generally your mpg will not go down in temps between 90F and 110F UNLESS you are running the AC. At 110F you should run the AC but expect your mpg to drop. Leave the AC off and your mpg will stay high but you'll die...... Or your battery will. lol
     
    #4 F8L, Jun 5, 2013
  5. Rupert B Puppenstein

    Rupert B Puppenstein Active Member

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    You shouldn't have a loss in fuel economy unless you are using the A/C. It has been warming up quite a bit in Atlanta these days, and the car has been saying the outside temperature is close to 90 degrees, so I try to keep the A/C on the lowest setting to avoid affecting the fuel economy much. Truth be told, my office is so cold, that by the time I get in the car, I don't need the A/C until about a half an hour into my drive. I am over 100 miles on this tank and I have 66 mpg. according to the car. (which is off about 2-3 mpg usually) I have no problem driving mostly on the battery these days, but we don't get to 110...well, knock on wood, I hope we don't!

    What kind of driving are you doing? City, slower speeds or Highway, faster speeds? It just sounds a bit weird to me.
     
    #5 Rupert B Puppenstein, Jun 5, 2013
  6. mmmodem

    mmmodem Senior Taste Tester

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    10% - 20% drop in fuel economy does seem excessive for AC use. But then again, 110 deg temp is quite the inferno. We don't have those kinds of temps in my area very often but losing 10% isn't unheard of. I think warmer weather being better for fuel economy only goes so far. At some high temperature, it asymptotes. I'd imagine increased AC and lower oxygen content in warmer air contributes to more engine use.
     
    #6 mmmodem, Jun 5, 2013
  7. Bingee

    Bingee Member

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    A/C will lower your milage. My ride loves the warmer temps but in Mich , we
    Don't get the high temps you get
     
    #7 Bingee, Jun 5, 2013
  8. fuzzy1

    fuzzy1 Senior Member

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    If not for this sentence, I'd say the battery is too hot from baking in the sun. But you have already tried to address that possibility.

    A previous thread had a similar problem in similar conditions, and no possible shade to park in at work. He had been using AC with recirc, and no AC with windows open. Once we got him using AC with fresh outside air and windows closed, forcing more cooled air through the battery vent, his battery cooled to a useful level part way through his commute. That brought back EV mode and ICE auto-stop.

    Until better ideas come along, I'd revist the battery temperature, and try to push as much cool air through it as practical. AC on, windows closed, and no recirculation in order to build additional pressurization to push air through.

    PS. Is the battery fan working? My climate doesn't force it on, but others have commented on its noise when it cranks up to full speed.
     
    #8 fuzzy1, Jun 5, 2013
  9. MarvHein

    MarvHein Junior Member

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    Not sure if the battery fan is working. How do I test it?

    In this case, I removed the passenger side dash vent and shoved my shop vac hose into the opening. (Hey, I commute alone, so the black hose running alongside the seat into the back seat is hardly noticeable!) Closed all the other dash vents and watched the battery temperature come down fairly quickly on the ScanGauge. This leads me to believe the fan is working or the dash fan shoved enough cool air over the battery.

    Within the first ten minutes, I also didn't see the ICE auto-stop even if the AC was switched off for 20-30 seconds, so it isn't the AC causing the ICE to run. Turning off the AC when stopped did drop the ICE RPM 200 revolutions from about 1200 to about 1000 but the ICE did not shut down. Why it would start shutting down later on is a mystery to me... the battery temps had been low much later and the inverter temp never fell. While the ICE auto-stop eventually happened, EV mode was not restored in any reasonable way during my 30 minute commute on highway mixed with side streets, even when battery temps fell into the mid-80's, which is usually perfectly fine.

    Running at night, my inverter temps stay lower. Around 122 last night, I didn't see any issues. I have a feeling there's some spot between 120 and 130 that things start getting icky, which is why I'm curious if anyone has any strategies for further cooling the inverter.
     
    #9 MarvHein, Jun 6, 2013
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