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It's the other way around. The fan clutch is the main fan at idle and low speeds. The aux fan is....auxiliary. Only kicks in when the fan clutch can't keep up and when AC is on.
That is so wrong! On the M5 the aux fan is the primary cooler and the mechanical fan is secondary. That is obvious if you just look at the activation temp and compare it to a 540. The M5 activation is a higher temp, and when you consider the operating temps of the two motors, one would say it is considerably higher. That is the OPs most likely problem short of some odd mistake on assembly.
 

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Here's exactly what I said via TIS. It's same thing with any other fan clutch engine
Regardless of what that general statement says, there is a BMW statement that it does not work the same as other BMWs. It might be in the techs introduction manual, not going to waste my time looking. It has been posted here 100s of times. So use your brain and think it through. The M62 operates 25 degrees hotter than the S62. The engagement for mechanical fan for the S62 should be less than the engagement temp on the M62. It is not it is ~15 degrees hotter from bad memory but none the less it is hotter. Albeit the temp of the exhaust air is different than reading the output temp of the coolant. This part seems to be the same on all cars. Clearly with the higher temp engagement on the fan it does not work the same as the other models in that statement which all share the same engagement clutch.
 

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Everything was put on genuine BMW parts, not worldpac.
OP you need to do some other things before you throw your new fan in. Before the recall this was the fan that was catching on fire. It does not catch fire anymore but it still burns up which causes big loads on the electrics. The failure starts by taking out the slow speeds then at the end there is often a large surge which burns the rest. There is a fuse behind the fuse panel in the glove box that has a 50/50 chance of being burned up. Then the wires from that fuse have been heated so badly that the insulation gets hard and can fail.
You might want to take the old fan apart and see how bad it burned up. To give reference this was mine and the fuse was blown and eventually I found a short piece of wire that needed to be replaced but not much. Others have reported much worse where the whole wire needed to be replaced. The fan will still look spotless on the outside.
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This is a thread I started a long time ago and although it is not helpful there are a couple of great linked threads in it. The one thing that you can grasp from it is all the technical writing can't be trusted. From the fan that should have been in the car to the temp of engagement of the mechanical fan. Also the wiring in the WDS. The wiring diagram from this thread should work for all cars delivered to CAN(all CAN car have the cold weather package, might be why they don't follow the standard info), if yours is a US car it maybe different.
The aux fan should be running 100% of the time(except turns off at a specific road speed) when the AC is on and if yours has not that might have helped cause the heat to climb.
It is climate dependent, in my neck of the woods the mechanical fan may never turn on, likely do to colder ambient air temps.
 

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Without access to INPA is there a way to test the aux fan direct outside of the care. Example checking a spare used?
Not sure I got your full question. The simple way is to turn the AC on with the car warm. Depending on the model year and package it will turn on immediately or there might be a short delay, but it is short. My guess is the later cars use more of the other two sensors that watch the AC system.
Don't think we ever got to testing the supply control voltage to emulate what controls the speed. You need an oscilloscope for that, I am sure this was on 68's list but don't remember him doing it. My tests with a 9v battery did not yield expected results. So as far as I know we have no idea if a short pulse makes the fan run slower or faster. A near 5v constant signal might make it run slow, or a slow pulse of 5v might do that.
Really all you can do is run the AC and see if it works. We also have no idea what the car uses to decide what speed to run the fan at, there are two pressure sensors on the AC, then there is the lower coolant output temp sensor, and last road speed that come into play. If you are having issues with the AC, or road speed sensors, and don't have the cold weather package or you car is later than the official change to the 3 wire system, your results may vary.
That said turning on the AC with the car parked in the drive warm has been a reliable way to find many a bad fan, before they start the burning up process because it seems pretty clear the lower speeds go first even though full speed may last for a longer time before it fails.
My suspicion is the damage to the fuse and wiring happens when only the full speed is working, but that is just a guess from where the damage has been found on the board posts.
 

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Just figured there was a way to bypass whatever it is to rule out the Aux fan itself as the source.
The volts are too low unless the battery is low so you might have the full blown issue. Sometimes the fuses don't blow just melt the holder and cause resistance, and then there is the damage that can happen to the wire. I think you need to follow the link in my thread to sleepers thread. His car was far worse than mine and he gave some good steps on how to figure it out.
 

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CONCLUSION: The only thing left to do at this point is to replace the heat exchanger. When i rebuilt the engine i cleaned it properly with hot water, checked for flow or debris, none found. AFTER this i am clueless. Feels like a very minor restriction of flow somewhere. Anyone ever replace oil filter housing?
That does not add up. First I would check that the previous owner has not got into the software and changed the buffer for the temp sender. Those gauges are meant as idiot switches and are buffered. If the buffer was removed it might report minor changes that were normal but unseen with the standard software. The other thing to check is the plug that connects to the temp sender. More than a few owners have had to lightly coat the pins with solder because the plug does not make solid contact. I forget the details and symptoms but there are some threads. 68FB discovered that and opened at least one thread on it so search his handle in the search.
Your problem is either air flow or water flow. Maybe the tensioner is weak and at low RPM the belt slips a little. I doubt that but the heat exchanger seems like a stretch. The heat exchanger is working on partly heated coolant and there is a time function there too. It also seems to work since both temps go up together.
Next time you are rolling to a stop bring the RPM up a bit which will raise the water flow and should change things. If there is a noticeable change that would point to water flow rather than air. That said increased rpm should produce more heat so if it is an air flow problem the temps should get hotter, but watch how fast those changes happen. The speed at which those changes happen may support the idea that your buffer has been removed, which is still my bet.
Edit I am still thinking about the #3, might change my bet to a poorly connected sender as that seems to be erratic and I believe that is the number one word used to describe that problem.
 

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Having my problems getting my head around this issue. It might be a couple of things together. No idea what, but we will get there. So lets do some checks, the first is open the secret menu and put Ktemps up and compare that to your gauge always, you might be doing that already, but state it. Two of the pins from the sensor feed the gauge and two feed the Ktemp reading, basically. The Ktemp is not buffered. When you first start the car cold and watch the temps you should see when the t-stat opens. When the T-stat opens it dumps a bunch of cold coolant into the system. If the buffer has been removed you will see a drop in the gauge, if it is still there the gauge just sort of hangs a little under 80 or normal position. The Ktemp will drop. Again read both the gauge and Ktemp you could also look at the oil temp but I forget which that is in the secret menu.
Also pay attention to the time that it takes for startup to the t-stat opening and then when that become stable indicating the coolant is all at the same temp. I think it is 5 mins to open then 7 to become stable. Also note when you get warm air out of the vents. Maybe this is the heater valve being frozen, just pulling strings. Next when you see the temp rise at some point crank the cabin heat up and turn the fan on high, it is a great uncontrolled rad that can actually make the car run cold this time a year in Ontario. Yes I know your problem is warm but it is a detail. If that has no effect it will say something. Not sure what but we will get there.
Did you replace the T-stat seal when you replaced the T-stat? Usually makes the car run cold but I am just looking for connections and data points. I am assuming you checked the condenser when you had the rad out but if it was plugged that will still effect how much air goes through the rad.
 

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I have no idea how the [email protected] this is related to car running too hot, because as far as i understand it's just for heater while the engine is at idle.
No it does more than that, in short it redirects coolant depending on a few things but mainly temp. Glad you got it fixed though. The valve is really about pushing the warm coolant from the heads directly into the cab heat on cold startup and times when cab heat is questionable. The outlet for that is right by the temp sender which explains the temps for the coolant going up but not really the oil temps. That will be for another thread.
 
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