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Thread: Auxiliary Cooling Fan

  1. #1
    Join Date
    Sep 2018
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    1999 740iL

    Auxiliary Cooling Fan

    I have a 2001 740iL with an auxiliary cooling fan that I do not think is working. It doesn't come on at startup, when I turn on the AC, or after car has been running a while with AC on in hot weather (Phoenix). I have never had a check engine code stating that there is a problem with the fan but have just never seen/heard it on. I changed the thermostat and auxiliary fan switch (located in lower radiator hose) about 4 months ago when I changed all cooling parts at 100,000 miles maintenance. I also checked the 50 amp fuse (F78) and it is fine. The fan is very expensive (approximately $500) and a relatively big job (remove front bumper, etc.) so I would like to be sure it is not working before changing it. Is the auxiliary cooling fan on a 2001 740iL supposed to come on when you turn on the air conditioner? I've read in the Bentley (170-3) that after 9/1999 through the 2001 year that activation of the fan is based on inputs from the ECM: radiator outlet temperature; calculated catalytic converter temperature; vehicle speed; battery voltage; and calculated refrigerant pressure. It also states that "when A/C is switched ON, the electric fan is not immediately turned on" which is in conflict with multiple BMW mechanics that have told me that fan should be on if the A/C is on. Any suggestions to diagnose if there is a problem? Thanks for any help.
    Last edited by 83EWMB; 09-24-2018 at 12:04 AM.

  2. #2
    Join Date
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    E39 fan will work as well and is a direct swap...

    https://rover.ebay.com/rover/0...com...2F281985795303

    Sent from my SM-N910T3 using Tapatalk
    Last edited by purplecty; 09-24-2018 at 08:07 AM.

  3. #3
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    All that you describing sounds like your aux fan is working...what problems do you have?

    Sent from my VS995 using Tapatalk

  4. #4
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    I agree with asianvenom. All appears to be working, no overheating, A/C working well, no codes, etc. The reason I question this is due to a BMW mechanic told me if the A/C is on then the auxiliary fan should be on. I started checking and even after in city driving with A/C on, the fan still didn't come on. I've never heard or seen it on. I was checking here hopefully to see if there is a way to verify that the fan/system is working.

  5. #5
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    Give it a drive, then let it idle at temperature, it should kick on after idling a bit. Also fan should be on when AC is on, but must be based on some condition, such as outside temperature. I've have seen when i turn the ac on, the fan don't kick on right away, but it turns on eventually.

    Sent from my VS995 using Tapatalk

  6. #6
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    1999 740iL
    Thanks for your suggestion. I have acquired another 2001 740iL auxiliary fan (off wrecked vehicle) so I will plug it in at start up and then after car is warm and idling as suggested by asianvenom.

  7. #7
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    These thing rarely go bad...what goes bad are the actual motor itself, there isn't much to it to go wrong.

    Sent from my VS995 using Tapatalk

  8. #8
    Join Date
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    99 840ci Sport Indv
    Just to confirm, unlike the auxiliary fan on the pre-facelift models that DO come on as soon as a working A/C is switched ON, the facelift 3-wire electronically controlled auxiliary fan doesn't. It depends on a number of other factors such as ambient temperature, evaporator temperature and refrigerant pressure.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  9. #9
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    Quote Originally Posted by Timm View Post
    Just to confirm, unlike the auxiliary fan on the pre-facelift models that DO come on as soon as a working A/C is switched ON, the facelift 3-wire electronically controlled auxiliary fan doesn't. It depends on a number of other factors such as ambient temperature, evaporator temperature and refrigerant pressure.
    There you go...

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  10. #10
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    BLK 01 sp, 20 Trail Boss
    My 2001 sport auxiliary fan never came on and the car never overheated ... A couple Indie shops tried to figure it out but none could locate the problem. It turned to be my DME, coolant had traveled up the loom from the thermostat and corroded the pins. Once I got a new DME it's worked perfectly ever since. Actually a used DME and Dudmd put my vin in it and I synced it that was about 4 or 5 years ago

  11. #11
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    1996 740iL
    Some info on the bottom half of this page.

    https://www.bimmerforums.com/forum/s...1#post27641431

  12. #12
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    1995 Dinan 740il
    I hesitate to comment as my knowledge is restricted to a 1995. That said, the bumper was super easy to remove (it's handy to have a 2nd set of hands to put it back). On mine the the external resisters had failed and $20 worth of replacements solved the fan's problems. See here and on E38.org for testing and replacement write-ups.

  13. #13
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    '01 740iL#2,'02 CBR954RR
    Quote Originally Posted by purplecty View Post
    E39 fan will work as well and is a direct swap...

    https://rover.ebay.com/rover/0...com...2F281985795303

    Sent from my SM-N910T3 using Tapatalk

    Wait what? the E39 fan is a direct fit with the E38 fan? is this true for M62TU's (2001 740iL) Purp? I need to replace mine, but OEM ones are going for $500+
    "A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering." - Freeman Dyson

  14. #14
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    Quote Originally Posted by kahlilj View Post
    Wait what? the E39 fan is a direct fit with the E38 fan? is this true for M62TU's (2001 740iL) Purp? I need to replace mine, but OEM ones are going for $500+
    Yes it is a direct swap! I have an eBay Topaz branded E39 fan in my e38 for a few years now. I think I paid $100 and the part number is 64546921395
    Last edited by purplecty; 11-28-2022 at 07:36 PM.

  15. #15
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    Quote Originally Posted by purplecty View Post
    Yes it is a direct swap! I have an eBay Topaz branded E39 fan in my e38 for a few years now. I think I paid $100 and the part number is 64546921395
    Kool! thanks for the tip!
    "A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering." - Freeman Dyson

  16. #16
    Join Date
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    Quote Originally Posted by kahlilj View Post
    Wait what? the E39 fan is a direct fit with the E38 fan? is this true for M62TU's (2001 740iL) Purp? I need to replace mine, but OEM ones are going for $500+
    Yup, E39 fans fit the E38. If you're interested, I've got a very lightly used one for an M62TU car sitting in my garage that I'd be happy to sell. It was in the car for about 500 miles before I decided to do a full electric fan conversion and removed the aux fan.

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