cooling fan problem??

Discussion in 'General Motoring' started by Mickey, May 10, 2004.

  1. Mickey

    Mickey Guest

    Noticed something new today and not sure if this is normal or not.

    Replaced thermostat this weekend and all appeared to be OK. While running the
    engine to purge any entrapped air, noticed the cooling fans coming on and
    cycling on a regular basis but duty cycle was probably less than 25%. Today I
    noticed that every time I came to a stop the cooling fans would come on
    immediately and stayed on until I was moving again. I live in a somewhat rural
    area and no stop and go driving 40mph or more is quite easy. Weather is cool
    (60°) & wet. Even had the heater on low. I don't think the fans were acting
    this way before the repair but recently weather has been warmer that today.

    New thermostat is stock temperature and temp gage is reading in the same area as

    Thought was maybe due to ambient temp the AC was coming on with the heater to
    dehumidify the air but checked and AC is not running.

    Anyone got an idea of what I'm seeing? TIA

    Mickey, May 10, 2004
    1. Advertisements

  2. Mickey

    Edward Hayes Guest

    Are you sure that ALL the air is purged from the system. Recheck overflow
    bottle when cold to see if more fluid has been sucked into the radiator. ed
    Edward Hayes, May 11, 2004
    1. Advertisements

  3. Mickey

    Kurt C. Hack Guest

    Did you have the defrosters on? The defrosters will activate the AC to
    dehumidify the air and to make sure that the seals stay oiled during the
    winter months.

    Kurt C. Hack, May 11, 2004
  4. Mickey

    Mickey Guest

    Water level has stayed consistent for last several days. Have even pulled a
    small vac on the radiator and saw no drop in fluid level due to entrapped air.

    Mickey, May 11, 2004
  5. Mickey

    Mickey Guest

    Defroster wasn't on yesterday and I did mention AC compressor not running.

    Anyone know the temp that the cooling fans come on at? Possibly that temp is so
    close to the thermostat that there is almost no difference and fan could come on
    at any time.

    On the other hand I'm wondering why fans were coming on within a second or two
    of stopping and why never shutting off as long as I'm stopped. Why no cycling
    of the fans like is normal?

    Need to find the reason for this operation as I don't want to find myself in a
    overheated situation.

    Mickey, May 11, 2004
  6. Hi,

    Since none of the "usual suspects" seems to be your culprit, it may be
    time to swap out the radiator sensor that turns on the fan(s) and see
    what happens. My experience is that when the sensor fails, it usually
    causes the fans NOT to go on (overheating) but that doesn't mean yours
    couldn't be going the other way.

    OTOH, it's STILL possible to have air in the system, even though your
    overflow tank's not going down. When you purged the system, did you have
    the car on an incline (front wheels on ramps or whatever) to make sure
    air could get out? My Subie's not so bad about this, but I had a Toyota
    that would take a month to get all the air out after a coolant change.

    Best of luck!

    Rick Courtright, May 11, 2004
  7. Mickey

    Mickey Guest

    Rick Courtright wrote:

    Did some further testing and still not sure.

    Cooling fans are controlled via the ECU with input from sensor in the coolant
    manifold atop the engine. Manual says signal from sensor at 85°C should be 1-1.4v.

    I placed a thermocouple in the coolant and ran engine while fully warm at
    various speeds for several mins. Temps ranged from 175-185°F and fans were on
    full time. This is the temp the thermostat starts opening. Further test is
    still needed but hope root cause isn't the ecu.

    Maybe my continual post will help others or latecomer will see and have the answer.

    Mickey, May 13, 2004
  8. Mickey

    Mickey Guest

    Got to work on this problem yesterday and what I found was interesting and
    thought some others might find it useful.

    I had the chance to get over to my son's house where we had some test equip.
    Was able to see some real-time readings from the ECU via the OBDII port and
    laptop computer.

    From physical observation I noted with the car stopped and cooling fans on,
    within a min or two I could hold my hand on the upper radiator hose or top of
    radiator and it didn't feel that hot. Also noted the air coming off the
    radiator fans was cool and not what would be expected when engine temp was close
    to 93(200). After seeing this I switched the heater on full blast. Within
    several mins the measured temp had dropped to the point where the fans went off
    and they stayed off. This indicated to me the problem most likely was with the

    The measurements:
    The stk thermostat is rated at 78 (172) and I expected to see the engine running
    close to this but what I saw while driving was the engine was running between
    92(198) - 96(205) depending upon driving conditions, much higher than expected.
    Taking some other readings I found the cooling fans come on at 96(205) and
    shuts off at 91(196).

    As stated in original post the fans were coming on almost instantly when I came
    to a stop. Now I can see why.

    I pulled the new thermostat expecting to find is not functioning correctly but
    what I noted instead was the flow passage on the new thermostat was a lot
    smaller than on the original part. I took a couple measurements and did a quick
    calc. What I found was the original part had an opening of 1.43 sq in and the
    replacement part of .85 sq in. New part was Only 59% of the original. These
    number were based on area of opening dia not including restriction of the center
    support. Looking at the difference in the support design I would guess the new
    part actually was only flowing 50% of the old.

    Putting the old part back in and going for a drive I saw a 15-20°F drop in
    temperature. Back at the house the car idled for another 5 or so min before the
    fans came on.

    The replacement part was a Beck/Arnly, made in Germany, almost $20. I would
    have expected this part to be of high qlty in all respects but the reduced flow
    just won't cut it.

    Will have to drive to nearest city with a dealer so I can purchase a factory
    spec't replacement.

    Hope there is a lesson in here for all to learn from.

    Mickey, May 16, 2004
  9. Mickey

    Edward Hayes Guest

    Thanks Mickey; that's good information to file for later use. So many after
    market parts seem to be listed as OK, only to find out that they only fit
    the mounting bracket. I once got a pair of Monroe shocks for my 86 Saab that
    were support to be valved and recommended by the Monroe book for my car. The
    darn things fit beautiful but were valved for a vehicle weighing probably 2X
    my Saab. I don't think the shocks moved at all when I hit a bump. Just
    because it fits doesn't mean it's the correct design. Ed
    Edward Hayes, May 17, 2004
  10. Hi,

    Thanks for the update! Looks like ANOTHER item to add to the "OEM works
    best" list! Not sure why Subies are so picky about factory vs
    aftermarket parts but they sure seem to be. My dealer parts guy jokes
    that aftermarket parts for Subies are all guaranteed: not to fit or work
    right! Several experiences of mine make me think he's right.

    Rick Courtright, May 20, 2004
  11. Mickey

    Mickey Guest

    Got the factory replacement part put in on Tues and took it out for an
    instrumented run. At speed engine temp was running 183-185F. Big difference
    than seen with the Beck/Arnley which had the car running at 198-205F.

    All is well with the fan operation again.

    Mickey, May 20, 2004
  12. Mickey

    Edward Hayes Guest

    I've had this problem with all makes of cars and not just Subaru. It may be
    more of a problem with low volume sales encouraging aftermarket suppliers to
    find something that fits the "hole" but not made expressly for any given
    vehicle. ed
    Edward Hayes, May 21, 2004
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.