2011 Prius Engine Swap High Speed Fans not kicking on

Discussion in 'Gen 3 Prius Technical Discussion' started by Ran4it2, Oct 14, 2021.

  1. Ran4it2

    Ran4it2 Junior Member

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    Hi there,

    Just swapped the engine on my 2011 Prius 3rd gen for the infamous head gasket issue. Changed out a new radiator and EGR cooler in the process.

    When idling in maintenance mode temps get to 203 but high-speed fans never kick on. I heard they come on at 204 but

    Low speed comes on when AC is on which is good. The scanner allows for high-speed fan control which works fine.

    We changed all 3 fan relays just in case, as it does have 231k miles. Heater blows nice and hot.

    So my question is when do the high-speed fans come on and is idling in maintenance mode around 199-203F normal?

    Thanks in advance!
     
  2. rjparker

    rjparker Senior Member

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    As I recall the fans come on around 205f unless already active because the ac is on. They are controlled by the ECM which also monitors temperatures and ac status.

    The dual fans are not directly two speed but use three relays (Fan 1, 2, 3) to connect them in series for low (each getting half the 12v) and in parallel for high (each getting 12v). I would suggest if your highest coolant temperature is 205f, the fan control is working under current conditions. Even if only low speed fan is used. Given the scanner can engage high speed, you should be good.

    In many driving conditions without ac, fans may not be used since there is adequate airfow caused by vehicle motion.

    Power fuses and relays supplying the circuit include EFI, RDI and CDS. Since the fans run under test these should be good.
     
    #2 rjparker, Oct 15, 2021
    Last edited: Oct 15, 2021
  3. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Did you put in a third or fourth gen engine? The latter are maybe more problematic, due to differences in coolant plumbing??
     
  4. Buzzhead

    Buzzhead Non-Interference w/ devel of pre-Warp civs

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    When I did my coolant change on my 2010 a few weeks ago, the fan wasn't coming on in maintenance mode, either. Used the old trick of keeping my foot on the gas to get the rpms above idle for a couple minutes. Fan kicked on.
     
  5. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I did mine last fall. After about 30 minutes without fan kicking in (in maintenance mode), I just shut it down, called it good. And it seems fine, at least in my case.

    I did run the car sim to the @NutzAboutBolts video, with the cap off the reservoir, but as @ChapmanF pointed out, you're supposed to fill it to a higher, top line (marked B) in the reservoir, and install the cap. During the warm up the level should drop, to end up roughly at the full line.

    More info in attached.

    Also worth noting: 2010 model year for sure have a bleed bolt, a black plastic gizmo with white cap, just above EGR components. It's good to have that open while refilling, till coolant flows out of it.
     
  6. ChapmanF

    ChapmanF Senior Member

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    I'm not sure you really see it drop during the warm up, because at the same time the coolant is warming up and expanding.

    What I've noticed each time I've done it is after the warmup, turning the car off and letting it cool all the way down to ambient again, the level ends up right on F just like the engineers knew the trapped air volumes pretty exactly.
     
    Mendel Leisk likes this.
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