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Discussion Starter · #1 ·
I have a strange problem with my 2001 M5.
The electric fan is running constantly, causing it to take an age to reach normal temperature from a cold start.
I have replaced the fan switch in the bottom hose, but it remains the same. The car has also thrown a thermostat code 'coolant temperature too low' e.t.c, however after driving for long enough, the temp gauge sits perfectly vertical and stays there.
I've only recently purchased the car, and it would seem its had the problem for a while, reason being when you shut the car off and the fan slows down, it makes an awful grumbling sound which I presume is worn fan bearings.

Any light that could be shed on this perculiar problem would be appreciated.

Cheers
Ben
 

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First, search on how to get to the "secret menu" and make sure your car is "heating up" to optimum temp. Do not go by "the verticle position" of the temp gauge.

If you see anything below 78-79 your T-Stat is shot.

I don't know what is going on with your electric fan, may be someone else can help you with that
 

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Does the fan run when the power is off?

The A/C system can also turn the fan on, so that's another option. Do you have the A/C turned on?
 

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Discussion Starter · #4 ·
The fan doesnt run when the power is off. If I kill the engine and then put it back on full electrics but dont start the motor, the fan doesnt run. I never have the A/C on either. I observed the fan starting earlier - it didnt simply start up and run - it jerked back and forth as if it had a bad contact somewhere, but then fired up and instantly went to full speed. I've run the car with the fan disconnected, and the coolant temp is perfect, however my oil overheats to just over 100C (it usually sits at 80).

-Ben
 

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That doesn't seem right, as the oil is not cooled by the fan at all, it's cooled by the coolant system. If you disconnect your fan and the coolant temp is perfect, but the oil overheats, then I have to wonder if your temp sensor is wrong.

The fan has the electronics built into it, it's controlled by a PWM signal from the ECU. It's possible the fan is bad, and just goes full speed when it shouldn't.
 

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Discussion Starter · #6 ·
That doesn't seem right, as the oil is not cooled by the fan at all, it's cooled by the coolant system. If you disconnect your fan and the coolant temp is perfect, but the oil overheats, then I have to wonder if your temp sensor is wrong.

The fan has the electronics built into it, it's controlled by a PWM signal from the ECU. It's possible the fan is bad, and just goes full speed when it shouldn't.
Those are now my thoughts exactly. I've now learnt the fan relay is built into the fan housing itself (within the motor unit?), so I thought maybe that was at fault. I called up the secret menu and the car settles at 86 degrees C on the motorway/highway, and never strays higher than the late 90's even when in traffic with the electric fan unplugged.

So I'll try thermostat (already ordered one), a new temp switch (the one in the thermo housing), then failing that, a new fan.

Fingers crossed....

-Ben
 

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Hi,
Are you sure your main fan (viscous clutch one) is working ok or your rad isn't blocked (leaves etc)? As those temps are high, therefore the Aux fan is always on (the Aux fan will kick in and always be on if the coolent temp is too high)
 

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Discussion Starter · #8 ·
The viscous fan is working for sure. I was always under the belief that the electric fan was 100% controlled by the fan switch in the bottom hose. Does the main temp switch have a bearing on the electric fan? And the fact it runs even when well below the 93 degree threshold of the switch is still a mystery. When I fit the new t-stat I'll flush the cooling system and back-flush the rad with the hosepipe to eliminate the possibility of a rad block.

-Ben
 

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Discussion Starter · #9 ·
Changed the t-stat this morning. The fan still runs, however I observed it in more detail today. When stone cold, it doesnt run. When the gauge is just coming up to the first dot, the fan kicks in on low speed, then within a minute it is running at full - stopping the gauge reading straight up. However if I unplug the fan and drive the car normally, the temps all behave perfectly (ktemp between 91-93 degs C).
So my next step is replacing the electric fan I guess, and hope the resistor pack is dodgy :dunno:

-Ben
 

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Changed the t-stat this morning. The fan still runs, however I observed it in more detail today. When stone cold, it doesnt run. When the gauge is just coming up to the first dot, the fan kicks in on low speed, then within a minute it is running at full - stopping the gauge reading straight up. However if I unplug the fan and drive the car normally, the temps all behave perfectly (ktemp between 91-93 degs C).
So my next step is replacing the electric fan I guess, and hope the resistor pack is dodgy :dunno:

-Ben
Not sure what your weather is like, but those temps are pretty high, especially if on a highway/motorway. Even in the brutal south Florida summers, I don't see those numbers on the highway. Something else is causing high temps, which your fan is reading and trying to kick on to remedy.

I would probably make sure the front and back of the rad is clear of all debris, and doing a coolant flush wouldn't hurt.

Regards,
Jerry
 

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Those are now my thoughts exactly. I've now learnt the fan relay is built into the fan housing itself
(within the motor unit?), so I thought maybe that was at fault. I called up the secret menu and the car settles
at 86 degrees C on the motorway/highway, and never strays higher than the late 90's even when in traffic
with the electric fan unplugged.

So I'll try thermostat (already ordered one), a new temp switch (the one in the thermo housing), then failing
that, a new fan.

Fingers crossed....

-Ben
Changed the t-stat this morning. The fan still runs, however I observed it in more detail today. When
stone cold, it doesnt run. When the gauge is just coming up to the first dot, the fan kicks in on low speed, then
within a minute it is running at full - stopping the gauge reading straight up. However if I unplug the fan and drive
the car normally, the temps all behave perfectly (ktemp between 91-93 degs C).
So my next step is replacing the electric fan I guess, and hope the resistor pack is dodgy :dunno:

-Ben
Hi Ben,

The info above points clearly to the fact that your cooling temps are running excessively high (as pointed out by
others, as well). With a full-flowing radiator (coolant side), no obstructions to airflow across radiator, new thermostat
and a properly operating viscous fan clutch, your coolant temp (as observed by Ktemp) should be rock-solid at
78-80 deg's while at freeway speeds, regardless of whether the electric pusher fan is connected or not.

The temp sensor (it's not a switch) located in the lower radiator hose, is used by the ECU to determine the temp
drop across the radiator. If the differential between the sensor located on top of the thermostat housing and the
sensor in the lower hose is insufficient and the lower hose sensor reaches the 93 deg switching point, the ECU
starts the pusher fan. This is what is happening here.

Your electric pusher fan is now toast (per your description of the sound/noise it makes) and should be replaced.

You said the viscous fan clutch was OK, but I doubt it. If it has never been replaced, or has more than 50-60K
miles, replace it. Replace the plastic fan with it. The blades become brittle over time and you run the risk of one
or blades separating, causing significant peripheral damage.

I highly suspect you have a large amount of debris distributed across the front face of the radiator. There is no way
to see, let alone check/clean it without removing the upper mounting support and primary cooling fan assembly, then
tilting it back, towards the engine. Ideally, you should just pull the radiator out. Then you will be better able to reverse
flush both the coolant and airflow paths. Virtually guaranteed, you will be quite surprised when you see the amount
of debris on the front side. For cleaning the coolant path, get some cooling system cleaning concentrate and mix
with just enough really hot water to completely fill the radiator while it's laying face-down. Let it set for a while,
drain out the cleaning solution and then reverse-flush with a garden hose. If you sense that the flow coming out
of the upper hose connection is less than expected, replace the radiator. Do not attempt having a radiator shop
"fix" it, it isn't worth it. By the time the coolant tubes get to the point of significant restriction, the connection
joints between cooling tubes and tank-ends will develop pin-hole leaks in short order after the radiator shop has
"boiled-out" the core.

Good luck getting it sorted,
Alan
 

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Hi mate,

I think you Aux fan is fine (by the way they all start will the juddery motion, as they start to recive 'start' pulses from the DME, so thats normal). As said before your temps are too high, so the aux fan is kicking in to keep things cool. The temps are either genuine high, or reading high cos of a faulty temp sensor. If you are still getting a peake code 69 (temperature implausibility) after your T-stat change, then I think this could indicate one of your temp sensors is at fault. If not then it seems somethings not right with your cooling system (debris, blockage etc),

PS if you want to check your Aux fan in isolation, when the engine is cold, start it up, turn the AC on to max (either by hitting the max button or manual set the cabin temps to 16C), then go out and watch the Aux fan for upto 2 mins, if your Aux fan is ok it will run (it will start with a juddery motion, then spin up to normal speed).

PPS
The outside temp has to be +5C for the AC to run, but it is quite warm in the UK at the moment so the above test should be ok.
 

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First and foremost, I apologize for thread hijacking but figured it would be best than to start another thread on this subject. I too just started having this problem where my aux fan began running constantly this evening. My temp gauge is mostly dead center and sometimes falls a few hairs over to the blue side. However, this evening I've noticed that the aux fan has been running full speed while my temp gauge is towards the blue side. No AC on and I was doing stop and go traffic for about a good 50 minutes round trip. When I turn off the car the fan shuts off and after restarting the car the fan kicks in about 30 seconds. I have 116K miles but no records of any coolant parts replaced. I will research on the secret menu to view the actual temp during warmup, etc...

OP, have you had this issue resolved?

EDIT: Oil temps are normal if that helps.
 

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Discussion Starter · #14 ·
First and foremost, I apologize for thread hijacking but figured it would be best than to start another thread on this subject. I too just started having this problem where my aux fan began running constantly this evening. My temp gauge is mostly dead center and sometimes falls a few hairs over to the blue side. However, this evening I've noticed that the aux fan has been running full speed while my temp gauge is towards the blue side. No AC on and I was doing stop and go traffic for about a good 50 minutes round trip. When I turn off the car the fan shuts off and after restarting the car the fan kicks in about 30 seconds. I have 116K miles but no records of any coolant parts replaced. I will research on the secret menu to view the actual temp during warmup, etc...

OP, have you had this issue resolved?

EDIT: Oil temps are normal if that helps.

Hi
The outcome was actually very simple (and something I should have checked first). After replacing the thermostat, temp sensors e.t.c e.t.c, it turned out that my viscous fan clutch was old and weak, and wasnt hooking up when the engine got hot, therefore not allowing the main fan to do its job.

I replaced the clutch and everything was fine - average temps dropped, the auxiliary fan only came on with the A/C and that was that. My one piece of advice (which no doubt everyone on the board would agree with) is REPLACE THE FAN TOO!! About 2 days later with the new clutch in, my old brittle fan threw a blade off, luckily missing coolant pipes and the rad, just causing the engine to run lumpy because of the imbalance of the fan - a new one was fitted and the car ran sweet again.

So just have a search for 'newspaper test' or 'viscous fan test' and start there.

-Ben
 
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