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When should the radiator fans come on?

Discussion in 'Gen 2 Prius Technical Discussion' started by nh7o, Aug 6, 2012.

  1. nh7o

    nh7o Off grid since 1980

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    I got back from a typically hilly drive, ambient temps about 27C at the most. At the bottom of my driveway MG2 temp was at 70C after a major uphill climb, and after crawling up my long steep driveway, the MG2 temp climbed up to 85C. This is measured using Priidash. No driveability problems.

    After I put it in park, I got out and opened the hood expecting to see the radiator fans turning, but they were not. Under what conditions should I expect them to be running? Seemed like plenty of heat needing to be moved.
     
    #1 nh7o, Aug 6, 2012
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The radiator fans will run if 1) the air conditioner compressor is running or 2) the engine coolant temp is high enough to trip the thermostat switch that turns the fan on.

    Note that neither of these conditions depend upon MG temperature.
     
    #2 Patrick Wong, Aug 6, 2012
  3. Britprius

    Britprius Senior Member

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    Perhaps in hot climates a good modification would be to fit a small fan to cool the inverter and transmission rad either permanently on when ready or controlled by a thermostat.
     
    #3 Britprius, Aug 7, 2012
  4. nh7o

    nh7o Off grid since 1980

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    I have been looking at that possibility. I don't think there is enough space to fit much of anything under the hood. But the control circuit for the fans has a slow speed mode that runs the two fans in series connection. Turning that on would not be difficult with another switch. A/C operation also turns that mode on, but I don't always need to run the A/C. It is not so hot here, but steep.

    The problem is that MG2 is a big chunk of metal that is not really able to be cooled well from the outside, via case conduction by air or the coolant loop. Although the temps I see are well below the DTC setting level (112C !! ouch!), and I am assured that it is designed to take some heat, the EE in me just doesn't like hot windings from a longevity point of view.
     
    #4 nh7o, Aug 7, 2012
  5. Britprius

    Britprius Senior Member

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    The heat in the inverter electronics cannot be good either, I know they are reliable but heat stress on any of the ic's output devices and capacitors cannot improve longevity or reliability.
     
    #5 Britprius, Aug 7, 2012
  6. nh7o

    nh7o Off grid since 1980

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    I agree. While the system is obviously robust, given the number of 200K+ mileage cars out there, most things are designed to last through the warranty period and I very much want mine to last longer if possible. Especially as I am operating on the margins of the design envelope.
     
    #6 nh7o, Aug 7, 2012
  7. uart

    uart Senior Member

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    Hi nh70. Just wondering, was the long slow drive up the driveway in EV mode?
     
    #7 uart, Aug 8, 2012
  8. 2009Prius

    2009Prius A Wimpy DIYer

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    Sure cooler is better but as long as the inverter coolant pump is working then enough heat is being removed by Toyota design. I vaguely remember the warning T level is way over 100C so T in the 80s may look scary but really not that bad.

    Update: found it:
     
    #8 2009Prius, Aug 8, 2012
  9. nh7o

    nh7o Off grid since 1980

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    No, and I don't think it would make it up in EV mode anyway. Not enough amps available to make the grade. MPG going up the steep bit shows about 5, so both systems are adding their share.

    My mission...to boldly go where no Prius has gone before.
     
    #9 nh7o, Aug 8, 2012
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