Question about viscous fan clutch failure
 

Yesterday after several minutes of idling and during low speed uphill crawling the car's temperature gauge started to creep past the midpoint. I stopped the car after just few dozen meters, before it even reached the next white mark in the gauge.

Today when investigating the issue I tried to replicate the problem of yesterday by letting the car idle for extended periods of time, tried also turning the A/C on and blocking the radiator with a piece of cardboard but the car didn't overheat this time. The coolant is topped and there are no leaks in the system, which leads me to believe the viscous fan clutch could be the culprit here. Also, for a past week or so I have heard some type of extra noise coming from the engine bay which to me sounds like it's coming from the fan, kind of like a failing bearing or something. I also noticed that the auxiliary fan is not working at all, or at least I was not able to get any type of reaction from it even with the A/C on, radiator blocked etc. If I recall correctly, with the E39 the auxiliary fan should make even some small movement when the A/C is turned on, not sure about the E53 but that didn't happen anyway. On the other hand, the outside temperature today was around 14 C (57 F), not sure if that is sufficient for testing.

My main question here is the reliability of newspaper test for the viscous fan. Today, after letting the car reach operating temperature, I rolled two newspaper spreads into a tube and stick it into the fan. In every test I performed, I was able to stop the fan with the newspaper. Although, I felt like it was little bit harder to do when I let my wife to raise rpm's but I was still able to bring the fan to a halt. Does this sound like the clutch is not properly engaging or is it completely normal to be able to stop the fan with the paper and the overheating was just because of the non functioning auxiliary fan?

I have been through this.

On my '06 3.0, both elec aux fan and clutch fan failed. Car overheated at idle.
You really need both fans working...replace your Aux fan...I went with the TYC brand with lifetime warranty...It was 1/3 the cost of Genuine.

The clutch fan should lock up when the radiator gets hot...not just engine. But if you can stop it with a small roll of newspaper, then you should replace it.

Don't buy the Meyle brand fan clutch unless you want your car to sound like a bus all the time. Behr / Sachs is a good brand.

BTW - Neither fan failure will trip a code...

I chose to just replace mine, with a favored/proven electric
 

Reasons why I switched from a viscous fan to an aftermarket electric fan (16" Flex-A-Lite #238/105390):
1 https://youtu.be/wm_gulIsxQ4 and

2) https://uploads.tapatalk-cdn.com/201...f3507480e3.jpg


Just after I got my X5 in '21, I was cautiously going over all the repairs and refits that had been done to it by the previous owner (who had bought it, and worked on it for 3.5 years, on my behalf, before we swapped vehicles), only a few items were overlooked, one of which was the mechanical fan. The aux fan worked fine, but I knew it wouldn't be enough to cool the engine, as summer was already there.

The '01's viscous fan was roaring, and upon inspection, I found a slight wobble in the viscous clutch, and chipped & cracked fan blades as well. I had always replaced mechanical fans on my trucks (and my dragrace '66 Chevelle) with the highest cfm electrics I could fit in, and to supplement the other fans they may have had already, for towing and/or being stuck in traffic (no speed-induced airflow). The exceptions are in my '04 Chevy 2500HD and '98 GMC, which still have their original viscous fans, and never needed any help with cooling.

Here's a thread I followed https://xoutpost.com/bmw-sav-forums/...ctric-fan.html, while over-complicating and/or redneck engineering my solution (as is my way), but the fan works as desired, keeping my M54 nice & cool, even in stop & go Texas summer traffic. I've never had a Flex-A-Lite fan fail (I do have a spare fan relay, just in case), and their blades never come apart, either.

When temp is hot the clutch should firm up and make it more difficult to stop. When mine failed I had no problem stopping it with my fingers.

The aux fan will turn about 1/8 turn when you first turn on the car but not AC.

The AC will not engage if the fan test fails at startup but the aux fan should kick on when the AC is on and the temp climbs.

The gauge on the dash is not a thermometer it's really a 3-position indicator and you reacted wisely to investigate when the needle came off the fake news 12:00 position.

The temp suggestion dial will be at noon over about a 30-40°C temp range which is ludicrous.

When the temp suggestion dial moved right the aux fan should have kicked in. Do you have a scanner that can run the aux fan like foxwell NT-510?

Other things that would present the symptoms you describe:

• mechanical clutch not engaging from temp
• aux fan not kicking on
• obstruction inside or outside radiator
• water pump impeller failure

That last one I've seen a couple time on xo in the past two years.

Monitor your *actual* temp to learn what temps are normal for your car you will see there's a range while the fake news needle points at noon.

Mine runs a URO part 11527505302 clutch and URO replacement fan. I can hear the fan engage quickly on a warm day or when the engine is hot. The AUX fan kicks on right away when it's hot and A/C is on.

Thank you all for the tips, based on this and being able to stop the fan with a tube made from newspaper sounds like the viscous clutch really has failed, so that will be replaced as soon as possible.

Andrewwynn's idea to test the auxiliary fan manually sounds good, I'll test that tomorrow with INPA. My guess is that the auxiliary fan is shot too, and in that case I'll replace that too. Water pump was just replaced and at least externally the radiator looks fine.

On e53 the quick test for aux fan is unplug the AC pressure switch it should spin the fan full power or close.

For a cooling fan, try a TOPAZ Condenser cooling fan #64546921381. It's brushless. It was 105F here yesterday. Out of curiosity, I decided to time engine off to aux fan complete stop. I can always hear it spinning after turning off the motor. Spinning time to complete stop was over 35 seconds! The fan spins effortlessly so I can trust it on hot weather days. Mine has run great for two years.

By this time, you need to do at least a partial cooling
overhaul.

Most important are WP (I use HEPU brand) and Thermostat (I use Wahler).

If you have a healthy cooling system, the fan clutch's role is less important.

Info on cooling overhaul is in forum, I wrote it around 2015 or so.