AUX Fan or AUX Fan Resistor

Hi Folks,
The Aux fan will comes on when (1) AC is on, (2) Coolant reached 103C. But don't see it coming on at slow speed at 91C. I guess the slow speed is gone.

So my question is, will just the Aux fan resistor P/N 67 328 371 873 for the resistor repair kit fix that? I don't need the whold Aux Fan assembly, right?

Thanks,
Ed

No one can really answer you question correctly since we don't know what engine you have. Please provide model, model year, build date. The e39 has multiple engines and changes occur at different times through the production run from 1996-2003

It is a 96 528

The kit more than likely will fix your issue. See the info below...although it is written for the e38...the e39's set up is similar. I'm posting pre-1996 & 1996-1998 because I can't tell if you have the 2 stage or 3 stage aux fan:

Thanks Qsilver7. That what I thought so as the fan did comes on when the ac is on and at high speed therefore I don't think the fan is dead.

As long as it is working when the ac is on don't worry about it,it is main job is to cool the condenser not the engine,if ur vc fan is operating properly i say forget it,it is only an assist for the vc fan,and in case the coolant temp is exceeding 104 i say check other places for troubles in the cooling system not the aux fan.

The VC fan does work, but I only hear it only once in a while as I did get over 104 only a few times. I guess replacing the resistor is not a ASAP job, but properly gets it out of the way before the summer is here. Currently, the temp. usually stay around 98 to 102. I would like to sees it goes down to 95C, as that os the temp I am seeing when the low speed fan is still working. As I got this E39 only a few months, so I am not too sure is it normal to have the temp being between 98-102. And I will usually start the heater after the temp reach 100C in order to lower the temp quicker.

Originally Posted by Ed Cheung

The VC fan does work, but I only hear it only once in a while as I did get over 104 only a few times. I guess replacing the resistor is not a ASAP job, but properly gets it out of the way before the summer is here. Currently, the temp. usually stay around 98 to 102. I would like to sees it goes down to 95C, as that os the temp I am seeing when the low speed fan is still working. As I got this E39 only a few months, so I am not too sure is it normal to have the temp being between 98-102. And I will usually start the heater after the temp reach 100C in order to lower the temp quicker.

There's no guarantee it would work with new resistor pack, my 97 doesn't work neither, but the 02 530 does.

Your engine cooling temp is a bit too high. I don't think your VC fan is working properly, maybe you need to replace your radiator, water pump, and thermostat too.

If it's up to me I will throw that VC fan in the garbage and replace it with an electric fan and set the temp sensor switch to 94C.

I agreed, the coolant temp at 98 to 102 really gets me worry. I am not too worry about the radiator, there is big different between the left and the right side of it, touchable on the lower hose vs burning my fingers at the upper hose. The previous owner filled her up with plain water. So I replaced it with coolant, replaced the water pump and the stat. The vc fan did had good resistance so I didn't bother to replace it, should had replaced it, as now I had to take it out again( What a pain in the A$$ job for pulling out out the VC fan).
I am not a big fan of VC fan neither, found them to be a bit in-consistant.

Originally Posted by Ed Cheung

I agreed, the coolant temp at 98 to 102 really gets me worry. I am not too worry about the radiator, there is big different between the left and the right side of it, touchable on the lower hose vs burning my fingers at the upper hose. The previous owner filled her up with plain water. So I replaced it with coolant, replaced the water pump and the stat. The vc fan did had good resistance so I didn't bother to replace it, should had replaced it, as now I had to take it out again( What a pain in the A$$ job for pulling out out the VC fan).
I am not a big fan of VC fan neither, found them to be a bit in-consistant.

there is big different between the left and the right side of it, touchable on the lower hose vs burning my fingers at the upper hose

Ed, this is not right you have air in your cooling system, after 20 minutes of driving both sides should be equal in temp when idling. M52 engine is a PITA to bleed.

Also don't ignore the expansion tank cap because if it's defective air can't get out.

Search for how to bleed the cooling system, I believe you have air in yours.

Yeah, it is pretty painful for burping the air out, but I had it good. Fill her up, get it to temp, loosen both bleeder nuts to see the bubble coming out until coolant coming out without bubbles, tighten the nuts, drive it for a few blocks and do the same thing over. Appox, 2 L more coolant went in after the bleeding process. And of course have the heater on to draw coolant into the heater coil. And now the coolant level is constance for a week.


No way, the corner of the radiator where the upper hose enter the radiator is always hotter than the corner with the lower hose enters the engine, as the coolant travel from one end to the other end of the radiator, the coolant gets cool off.

When the previous guy filled her with water I was loosing 500ml for every 3 tank of gas. At lease the evaporated water shows that the coolant cap is ok. I found this funny, the coolant expansion tank in my car is the clear color one, but it is tainted green from whatever the previous guy put in, and I always thought it is full by looking from the outside. Until driving it for a month, did a more details checking , only 1/3 full...with water....what a surprise.

I bet the car had the cooling system went south previous, that's why the water pump and radiator looks pretty new. And he haven't got to the electric fan and then sold it. I guess he sees the fan do comes on when ac is on and the fan do comes on when it reach over 104, and thinks that nothing is wrong and can't figure out why the temp is still at the high side.

No way, the corner of the radiator where the upper hose enter the radiator is always hotter than the corner with the lower hose enters the engine, as the coolant travel from one end to the other end of the radiator, the coolant gets cool off.

Yes way, the heat transfer function of the radiator only works when air flows over the fins. I did mentioned when engine is idling meant car is stop which there's no air flow over the fins and if engine is already at operating temp you will hardly can tell the different between the inlet and outlet, at least this is how both of my E39 cars act.

If you have air trapped in the thermostat housing, air doesn't conduct well to temperature it faked your thermostat not to open widely restricted the flow, the lack of flow caused temperature to rise.

When the previous guy filled her with water I was loosing 500ml for every 3 tank of gas. At lease the evaporated water shows that the coolant cap is ok.

Nothing wrong with using 100% water if you live in a climate that ambient temp never dipped below freezing point, as a matter of fact water has better heat transfer then any antifreeze cooling.

What concerned me the most is are you loosing cooling now? If you do your head gasket is busted. I hope this is not the case.

Try to bleed again but this time using cold bleeding method first.

Originally Posted by 16valex

Yes way, the heat transfer function of the radiator only works when air flows over the fins. I did mentioned when engine is idling meant car is stop which there's no air flow over the fins and if engine is already at operating temp you will hardly can tell the different between the inlet and outlet, at least this is how both of my E39 cars act.

If you have air trapped in the thermostat housing, air doesn't conduct well to temperature it faked your thermostat not to open widely restricted the flow, the lack of flow caused temperature to rise.

Yes, correct the heat transfer works when air passes through the fins over the radiator, that's why we have the vc fan constantly spining even at idle. And that's why the VC fan will spin faster when things gets hot and the Aux fan comes into play above 91C to move the air for heat transfer. And as the coolant travel in radiator, the fin keeps on robbing out the heat for it so more or less, the exit point of the radiator will be cooler. If you mount 2 temp sensor on both end of the radiator, for sure you will see the different in temp.

I bet it is hard to tell the difference if the car being warm at idle, the T-stat opening and closing also play it's part at affecting the temp shows on the radiator as well. If you let the car warm up to operating temp, it will reach right up to the temp of the t-stat opens. Most likely it is partially open and have a slow coolant flow to the radiator and closed the coolant went below the t-stat opening temp.

If you have the car drive around and reach up to the temp where the aux fan start to kicks in, you will feel the different in temp between both side of the radiator, as that's what the radiator suppose to do, takes in the hot coolant and cool it off as it leave the radiator.

Originally Posted by 16valex

If you have air trapped in the thermostat housing, air doesn't conduct well to temperature it faked your thermostat not to open widely restricted the flow, the lack of flow caused temperature to rise
Nothing wrong with using 100% water if you live in a climate that ambient temp never dipped below freezing point, as a matter of fact water has better heat transfer then any antifreeze cooling.

What concerned me the most is are you loosing cooling now? If you do your head gasket is busted. I hope this is not the case.

Try to bleed again but this time using cold bleeding method first.

I agreed, water is the best liquid for heat transfer, but the pressure it created, and being evaporated is annoying. I used both the bleed screw on the t-stat housing and the radiator, and had the coolant level stay the same for a week, so I rule out the air part.

The Aux fan is not working, so I guess that should explain the cooling system is not working properly. And the VC fan is a bit questionable now..... After switching from water to coolant, at the same temp, the hose is not pressurized so I am not having exhaust gas in the cooling system. For the save side, I will do a compression test on the cylinder over this weekend to make sure the gasket is ok.

Geeeeeee, I thought my Discovey was painful for the cooling system...........

Here are my conclusions.

Your aux fan is fine because my 97-528 the 91C doesn't work neither but engine temp never went passed 96C according to test 7 with OBC unlock. I understand that Qsilver has shown the schematic but it's from an E38, so I'm not so sure if 97 E39 really equipped with this, I went as far as replaced the dual temp sensor on the radiator to no avail.

I think your VC fan is dead time for a new one. Or, it's time to put an electric fan in there. Take a look at mine.

If you replace the resistors on your aux fan your ac will likely be colder. The aux fan runs constantly on low with ac, without low speed it will just cycle on and off in med speed too quickly. Your m52 running hot could be a lazy fan clutch not locking up early enough. I have a 97' with 210k and replaced both the resistors and f vc this past summer. Sachs fan clutch seems to be better so far. IMO No need to bleed while hot, just overfill expansion tank and crack bleeders to push out the air bubbles.

just roll a newspaper and carefully place it against the vc fan,if u can stop the fan it means it is screwed,or u can simply unmount the fan and check the clutch for silicone or oil stucked in its back along with sticking dust,the behr clutch usyally lasts for 4years in hot countries coz it is activated/ engaged more frequently.

I just check for resistance at the VC fan, so I will try the newspaper trick. I am leaning towards getting both done, the vc and also the resistor as well.
To be honest I hated VC fan, so I properly will try what 16valex had done

I re-read the Bentley manual, and here is what it said,
The electric cooling fand is mounted on the bumper side of the radiator.
In Models manufactured up to 9/1998 (M53 or 1997 M62 engine), the electric cooling fan is controlled by a dual temperature fan switch mounted in the side of the radiator.

Fan switch calibration(M52, M62 engine)
-------------------------------------------------
Electric fan activation:
low speed 91C (196F)
High speed 104C(219F)
------------------------------------------------------

In models manufactured after 9/1998 (M52 TU engine, M54 engine, M62 TU engine), the electric cooling fan is controlled by the engine control module (ECM) via the output final stage.
The output final stage is mounted .......

Originally Posted by JoePH

If you replace the resistors on your aux fan your ac will likely be colder. The aux fan runs constantly on low with ac, without low speed it will just cycle on and off in med speed too quickly. Your m52 running hot could be a lazy fan clutch not locking up early enough. I have a 97' with 210k and replaced both the resistors and f vc this past summer. Sachs fan clutch seems to be better so far. IMO No need to bleed while hot, just overfill expansion tank and crack bleeders to push out the air bubbles.

Hey Joe, I noticed you have a 97 too. I would love to hear if your 91C work? TIA.

Yes, and my VC fan is dead as well, confirmed with some rolled up newspaper.

Originally Posted by 16valex

Hey Joe, I noticed you have a 97 too. I would love to hear if your 91C work? TIA.

Mines a 5/96 btw. Actually I dont think it does, not til close to overheating and not on low speed. I recently unlocked the obc and temp rised above 91 for a few minutes while idling in a drivethru and I didnt hear the aux fan... Hope my resistors didnt crap out again. Next time wont be oem if so.

Originally Posted by JoePH

Mines a 5/96 btw. Actually I dont think it does, not til close to overheating and not on low speed. I recently unlocked the obc and temp rised above 91 for a few minutes while idling in a drivethru and I didnt hear the aux fan... Hope my resistors didnt crap out again. Next time wont be oem if so.

I have a feeling that our cars the 97 and 98 don't come equipped with 91C software trigger low speed aux fan. I went as far as replaced the dual temp sensor and new resistor pack to no avail. I don't trust Bentley manual neither they are pathetic.

Thank you Joe for your input.

I had a feeling that this is going to be the case.

Originally Posted by Ed Cheung

I had a feeling that this is going to be the case.

So to save your money and time don't bother with a new resistor pack. As long as it turns ON when you have your AC on you are all set.

Now, do something about your VC fan and let us know how that go. Hope it will resolve your high temperature reading. Good luck.

Yeah, I rather use the money for the electric fan controller that will replace the VC fan.

OK, got a replacement fan clutch, to my surprise, I can still stop it with a rolled up newspaper, the resistance felt pretty much the same. But at idle, for sure it is pulling more air. The result?! It is pretty much the same now it is between 97-100 with or without ac. When driving at highway, it is staying at around 97 or 98 now VS previously had the heater at full blast to keep her at 98. And at idling she is right on at 95C. To give you more details, I drive 10km x 2 everyday with plenty of up and down hills. Average speed is 29.5km/h as registered.
I don't know anyone around me with a e39, had a bunch of them with e36, friend's friend may have a e46, I will ask them to try to unlock test 7 to see the temp at normal driving.

A little side story here, previously I use the tennis ball to jam the pulley and the belt in order to loosen the fan clutch with a wrench, it works but have to place the tennis ball in a perfect position, but I was in a rush today, just use a BIG flat head screwdriver, place the tip on close to the edge of the fan clutch nuts and nail it with a BIG hammer, and it pop right out and replaced the old one in 5 minutes!