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Thread: FAN Power draw - H6 3.0 engine radiator fans from 2002 Legacy Outback

  1. #1

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    aquillen's Avatar
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    FAN Power draw - H6 3.0 engine radiator fans from 2002 Legacy Outback

    This probably represents high end of power draw for a Subaru fan setup, but the 4 bangers may well use just as much for their fans. These are a pair of used 2002 Outback LL Bean donor fans which I completely rebuilt, installing new bearings and recut/trued the commutators, so I believe they are good representative motors for this test. I'm posting this because another member asked what my max fan current draw was, so why not list the info I gathered just in case someone else could use this.

    Both fan motors are rated 120 Watts, so 10 amperes each is the rating. But the fan blades, atmospheric pressure, etc., determine actual power draw at max operation, and from testing at 12 volts, the draw is somewhere below 10 amperes for each motor. At a full 14.5 volts with running engine and a charged battery it is quite likely one or both would pull up there at 10 amperes but I didn't test that.

    There are two fans - main fan and sub fan, the two fans are controlled together by the ECU - both run at the same speed. The main fan has 7 blades and each blade is a bit more narrow than the wider blades on the sub fan, of which there are 5.

    Although they can be wired for up to 4 different speeds, the service documents shows 3 speeds are used. Speeds are selected by the ECU. One ground wire is always connected. Looking at just the main fan, a second ground is connected when the ECU energizes relay F31 which increases the speed capability depending on the ECU control of fan relays #1 and #2. Fan relay 1 enables partial speed, Fan relay 2 enables additional speed. (NOTE: The test procedure in the manual uses the wiring in a different configuration to test the motors, but the ECU determines fan speed via the 2nd ground relay and the two Fan relays.)

    Voltage measured with Fluke87, current with Wavetek CT233 clamp on meter.

    Battery voltages were applied at 2 inches from the fan motor's local connector plugs (chopped off connector pigtails not yet wired to car circuits). Since mid speed is determined by the ECU and I don't happen to know whether it does this by using both ground -or- both 12V leads, I only list the low and high speed current tests here. In any event mid speed will be somewhere between the low and high current draws.

    Refer to the drawing below.

    (5 amperes at Main fan slow speed) - F17 pin numbers:
    4 - Gnd
    1 - 12.3V

    (7.4 amperes at Main fan high speed) - F17 pin numbers:
    4 - Gnd
    3 - Gnd
    1 - 12.0V
    2 - 12.0V

    (6. amperes at Sub fan slow speed) - F16 pin numbers:
    4 - Gnd
    1 - 12.2V

    (9.0 amperes at Sub fan high speed) - F16 pin numbers:
    4 - Gnd
    3 - Gnd
    1 - 11.9V
    2 - 11.9V

    This is my project's schematic, adapted from the 2002 Outback factory drawings:
    Last edited by aquillen; 09-11-2019 at 02:06 PM.

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  3. #2
    Senior Member UnhipPopano's Avatar
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    We take it that you were testing the fans in a free standing mode. Does the load change if there is a radiator in front of it and using a shroud? Also, is it agree that for the situation where the car is on the road that the electric load will be less?

  4. #3

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    The fans were in the car, with the radiator installed and with the OEM fan shroud that goes between the fans and the back side of the radiator. Hood was not installed. I'd expect the load to change under more complete configuration but actually this setup would probably cause the highest power draw as it was tested. When vehicle is in motion I'd expect power draw to drop as speed goes up.

    I originally wrote that the ECU can control either fan independently which is incorrect. The following is correct:
    There are two fans - main fan and sub fan, the two fans are controlled together by the ECU - both run at the same speed.


  5. #4
    Senior Member Rob T's Avatar
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    Chad did an interesting thing with the two fans on the car he built (I now own). One fan is controlled by thermostat automatically. The other he put on a manual switch. Then you can run that fan in the paddock, even if the car is off or leave it on based on temperature when you are running. I have not needed it on the track at speed.

  6. #5
    Senior Member Jetfuel's Avatar
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    I'm running a two position switch, up runs the fans only, down runs fans and inter cooler water pump.
    It goes to the down position as soon as the car gets started

    Jet

  7. #6
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    My thoughts on fan shrouds: most fan shrouds block air flow everywhere except the fan area. This is wasted air flow. I’ve cut off all extraneous shrouding, leaving a small margin around the fan itself. I then welded on a preformed lip around the perimeter. This lip protrudes toward the radiator, but within 1/2” of the rad core. To that lip, I added a push-on bulb seal that contacts the rad core, effectively sealing the rad fan from air spillage. This allows an open area around the fan to pass air through when the fans aren’t running. When the fans are called for, they still pull air through their respective discrete swept areas. I’ve never seen anyone else do this, but I know it will work well. Mine is this way, but I’m only using a single 14” fan. I’m also using a dual pass rad, drop-in sbc aluminum unit. Fwiw.

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