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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 04-30-2017, 07:51 PM
DLSmith DLSmith is offline
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Overheating once again...

I have a 98 M Roadster with less than 25,000 miles. I have changed every cooling related component recently in an effort to keep the car running cool this summer. I now realize the real problem is that the auxiliary fan is not coming on. I have checked the fuses, jumped the fan and both hi and low work. I tested the auxiliary switch and it is working correctly. The fan does come on when AC is turned on. So now the question...what next? I need to figure this out before I slit my wrists.... Your help is appreciated.




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  #2  
Old 04-30-2017, 08:14 PM
Blacklane Blacklane is offline
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By "tested the aux switch", I assume that means the radiator temperature sensor, correct?
Do you have a Bentley manual with the schematics in the back? That is a big help in understanding the electrical circuitry. If not, the schematic posted at post #6 here should help: http://www.bimmerfest.com/forums/sho...d.php?t=385482

There is a known problem where occasionally the factory mis-wired the temperature sensor and reversed the high- and low-temp pins (black and green versus black and gray). Note that "SW" stands for "Schwartz", which is "black" in German.
It's also possible that the Normal Speed relay is bad, which will prevent both speeds from energizing.
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Old 04-30-2017, 08:36 PM
DLSmith DLSmith is offline
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Quote:
Originally Posted by Blacklane View Post
By "tested the aux switch", I assume that means the radiator temperature sensor, correct?
Do you have a Bentley manual with the schematics in the back? That is a big help in understanding the electrical circuitry. If not, the schematic posted at post #6 here should help: http://www.bimmerfest.com/forums/sho...d.php?t=385482

There is a known problem where occasionally the factory mis-wired the temperature sensor and reversed the high- and low-temp pins (black and green versus black and gray). Note that "SW" stands for "Schwartz", which is "black" in German.
It's also possible that the Normal Speed relay is bad, which will prevent both speeds from energizing.


Correct on tested the radiator sensor switch. Held while attached to the wiring and heated up and fan came on high. Assumed that the heat gun overheated for the low setting. I am ashamed to say that I do not have a Bentley manual as of yet. Need to order asap. Back to the incorrect wiring comment, I have read this prior but blew it off as hard to believe. However, need to pay attention to this now. I also read that the brown wire was to be in the middle. Mine is not. The Bentley would also allow me to find and test the correct relay. Your help is appreciated. Thanks.

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  #4  
Old 05-01-2017, 06:05 AM
DLSmith DLSmith is offline
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Blacklane, is it possible that the relay is bad even though the fan circuit works when jumped? Are you able to confirm that the brown wire should be the middle wire? Let me know and thanks.
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Old 05-02-2017, 04:44 AM
Bob2.8 Bob2.8 is offline
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Originally Posted by DLSmith View Post
Blacklane, is it possible that the relay is bad even though the fan circuit works when jumped? Are you able to confirm that the brown wire should be the middle wire? Let me know and thanks.

A mis-wired switch is not unusual.

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Old 05-02-2017, 07:50 PM
DLSmith DLSmith is offline
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Altered wires as outlined on above site. Took the car out for a good drive and found the fan did not come on at all. The temp gage approaches the second bar past center. Never having one of these cars I am uncertain where the fan should come on. The fan did come on when the AC was turned on. Your experience and help is appreciated.

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  #7  
Old 05-02-2017, 07:59 PM
khammack khammack is online now
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Have you checked that you have good circulation in the radiator? Maybe air in the system(?). Are both radiator hoses hot after a drive? If the water is not moving because of an air bubble, then it may not be tripping the thermostat on the passenger side of the radiator.
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Old 05-02-2017, 08:22 PM
DLSmith DLSmith is offline
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Yes both are hot. Have parked the car on an incline and brought to temperature. Watched the bleeder until no air came out at all. Did the same thing the next day. Once cooled brought level up to cold line. I feel pretty comfortable the air is out. The worst part of no fan is that I live in Phoenix an can't drive in the summer... but again, go your fans come on when gage goes past center?

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Old 05-03-2017, 07:01 AM
khammack khammack is online now
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After a hard autocross run, when I'm back in the paddock, my electric fan does come on sometimes. My gauge doesn't ever get past center though.
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  #10  
Old 05-03-2017, 07:33 PM
DLSmith DLSmith is offline
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Have an appointment for Friday. Time for the big boys to take look. Thanks for all your help.

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Old 05-04-2017, 04:52 PM
danomite danomite is online now
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If both hoses are hot, and the fan is not activating, then I'm guessing that your temp sensor (located on the left/passenger side of your radiator) is dead, or is not functioning correctly. If you're seeing the water temp needle move past halfway, that's not normal.
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  #12  
Old 06-13-2017, 08:55 PM
DLSmith DLSmith is offline
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Have an appointment for Friday. Time for the big boys to take look. Thanks for all your help.

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As a follow up, shop took a look and determined that the new BMW fan clutch was junk. Replaced and all is good. No Temps past half way. In Phoenix in the summer, that's saying allot... Thanks to all for their assistance

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  #13  
Old 06-14-2017, 03:40 AM
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vintage42 vintage42 is offline
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Originally Posted by DLSmith View Post
... the new BMW fan clutch was junk. Replaced and all is good. No Temps past half way. In Phoenix in the summer, that's saying allot...
So there never was a problem with the electrical fan?
Temp needle is controlled to stay halfway (vertical) from 165 to 225. When temp reaches 212 the aux fan comes on to knock it down to low 200s.
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Old 06-14-2017, 04:47 AM
DLSmith DLSmith is offline
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Good point Vintage42. Yes, I changed the brown wire on the electric fan sensor also. It was wired wrong. However inn Phoenix this time of year, the AC is always on therefore the electric fan is always on. But yes it works correctly now. Thanks for reminding me.
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  #15  
Old 06-14-2017, 06:19 AM
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vintage42 vintage42 is offline
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I don't understand how so many Z3s lasted for ten years or more with a mis-wired fan sensor. You would think that after the first summer in the southwest, the overheating would be investigated, with the cause found and corrected under warranty. I wonder if there was a tech bulletin on it.
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Old 06-14-2017, 07:03 AM
DLSmith DLSmith is offline
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I agree. That's why I had such a problem believing it could be true.
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  #17  
Old 06-16-2017, 12:23 PM
Z3notZ8:( Z3notZ8:( is offline
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Originally Posted by vintage42 View Post
Temp needle is controlled to stay halfway (vertical) from 165 to 225. When temp reaches 212 the aux fan comes on to knock it down to low 200s.
So if the engine is at idle, and the aux fan kicks on, will the fan run extremely fast when the car starts driving again?
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Old 06-16-2017, 04:41 PM
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vintage42 vintage42 is offline
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Well, I don't have an auxiliary / second fan. My electric fan is the only fan. It cycles on and off at hot idle. When the temp reaches 212 at a long stop light, the fan comes on, high/fast, for 10-15 seconds. It stops when the temp drops to around 200. It may take a minute for the temperature to climb back to 212 and turn the fan on again.

As soon as the car is moving a little, the fan does not come on again. Just 5-10 mph is enough airflow through the radiator to keep the temp at its normal steady 207.
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Old 06-18-2017, 12:42 PM
Z3notZ8:( Z3notZ8:( is offline
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So either way, as long as the temp gauge never goes above half, the fan running at extremely high revs is nothing to worry about?
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Old 06-18-2017, 04:04 PM
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vintage42 vintage42 is offline
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So either way, as long as the temp gauge never goes above half, the fan running at extremely high revs is nothing to worry about?
The gauge at half is good. The fan running at all to keep it there is not good. And the fan running at high revs to keep it there is bad.
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Old 06-20-2017, 07:02 PM
Z3notZ8:( Z3notZ8:( is offline
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The gauge at half is good. The fan running at all to keep it there is not good. And the fan running at high revs to keep it there is bad.
I have never seen the gauge above half. The fan comes on after a long idle time. The fan revs higher as I apply the throttle. It does not take long after that for the fan to shut off. I took it to a shop that regularly services German vehicles to have it checked out. At that time, there was seepage coming from the clamps not being secure at the heater core. The shop made the repair and said that there was nothing else wrong with the cooling system. I have not lost a drop of coolant ever since I topped it off after the repair which was last October or November.

Is there something I need to be checking to prevent my fan from coming on?
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  #22  
Old 06-21-2017, 03:46 AM
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vintage42 vintage42 is offline
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Originally Posted by Z3notZ8:( View Post
... The fan revs higher as I apply the throttle... Is there something I need to be checking to prevent my fan from coming on?...
From what I see, my electric and only fan is normally off, and has only two speeds -- low for whenever the AC is on, and high for whenever the temperature reaches 212. When it needs to run on high, it only runs a moment until the temperature drops.
Its speed does not vary with the throttle.
I don't know what to make of yours.
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