2000 BMW 540i: KTMP up to 116 and howling Aux fan since visco switch

[Franknstein]

Hi All

Got a 2000 540i - live in England.

Been driving all winter and its been good. Ambient temperatures increasing a bit recently as its Spring (yay!).

Here's the story.

1. I had noticed recently this spring that ambient temps are higher - and when driving around town when the engine had heated up that I'd get that really annoying fan-clutch whining sound... like it was locked solid and whirring away increasing in intensity with RPM. I had a nose about and turns out it was fitted with a poor quality repro. part by the PO. I trashed that and fitted a brand new BEHR/Hella from a reputable parts dealer (made in Germany).

2. Since then I have noticed the Aux fan comes on, where it never used to (or at least I never noticed it). And it comes on all the time now, and its LOUD, and annoying, and something is not quite right I suspect. This aux fan is the later type controlled by the ECU. I had a look about the fan and checked all my fuses as I suspected it was only running on HIGH mode. All the fuses for the Aux fan had been removed by the PO.?!? I put all the fuses back in for the Aux fan. Doesn't seem to have changed anything though. I have read the aux fan should come on immediately after switching on the aircon - it does not, it only comes on when engine heats up and then it seems to run really high speeds when in traffic/idling.

3. Since this ordeal started I have been monitoring KTMP readings on the cluster and in traffic its climbing to around 114... sometimes even 116 with the aux fan going mental, and bystanders wondering what's going on! On highway it likes to be around 107. If I put the heater on inside the car with cabin fan to max I can maintain 108KTMP indefinitely.

Yes I put the fan clutch fan on the correct way.

4. Coolant is full, and I'm not losing any either. I doubt its a blown gasket, well I certainly hope not. But no coolant loss, and a clean oil cap - coolant is clean too.

5. Radiator looks good, IE not blocked up.

I have read some stuff about BEHR not being any good. So I swapped the original BMW Behr from my E39 530 into this car today, and exactly the same symptoms - my 530 runs fine with that fan clutch so I am pretty certain its not the fan clutch causing these hot temps.

The temp gauge has never moved from 12 o'clock position.

So, really - just looking for advise as to where to turn next - not wanting to throw parts at the problem. My thoughts were to check the thermostat - possible its lazy and sticking a bit? At a bit of a loss on this one!

thanks
F.

[edjack]

Verify that the t'stat heater is working correctly, and is not electrically open. The two-wire connector shows the location, right on top of the t'stat.

You may be correct in suspecting the t'stat. How old is it?

The heater is driven by the engine computer (aka ECU or DME), and allows for increased coolant flow at high engine temps. I've seen my engine drop down to 95 deg in heavy summer traffic.

The aux fan is controlled by the ECU, which monitors the radiator coolant outlet temp.

The temp gauge is buffered. I don't remember what temp is required to drive the needle into the red.

[Franknstein]

Verify that the t'stat heater is working correctly, and is not electrically open. The two-wire connector shows the location, right on top of the t'stat.

You may be correct in suspecting the t'stat. How old is it?

The heater is driven by the engine computer (aka ECU or DME), and allows for increased coolant flow at high engine temps. I've seen my engine drop down to 95 deg in heavy summer traffic.

The aux fan is controlled by the ECU, which monitors the radiator coolant outlet temp.

The temp gauge is buffered. I don't remember what temp is required to drive the needle into the red.

edjack - appreciate the reply.

No idea how old the t-stat is - and yeah, probably an idea to change anyway, but still - I always like to diagnose faults first with good evidence - then get parts.

Tested the t-stat heater. Its got continuity across the two terminals. I also checked voltage on the plug and getting a steady 10.25V on that connector - funny thing is I can see it had electrical tape, unravelled it and it showed having been repaired at some point - IE the plug was cut off at some stage and its been reconnected with two spade terminals - it was a good job though, but it does beg the question - why?

messing with the fuses this afternoon, I decided to check if there were any others missing, and there was one of the two for the 'Heater' was missing, I reinstalled that missing one. Dont know if it will have any bearing on this problem - but I did it nonetheless.

Not sure where to next!

[theWalkinator]

Have you resolved the issue? I have the similar problem with my fan clutch, just wonder if you have fixed your problem.

[Franknstein]

Hi
No, not solved it. I'm taking the car off the road in a couple weeks to attend to multiple issues and I've bought a new thermostat, which I am hoping is the problem.
I'll post the outcome, but its weeks away.

F.

[Uturn540]

FYI the gauge needle will stay in the middle starting at 75c (167f) and stay there until temp hits 116c (241f), then will sweep up and hit the red at 120c (248f). The back side of the red area is 125c (257f). There is also the possibility that the problem may be the temperature sensor. There are actually two circuits on the sensor. One thing to try is to have the cluster to test 7 KTMP, when you park turn the key to position 1 (switches to the second circuit) and see if the KTMP changes.

[geargrinder]

IE the plug was cut off at some stage and its been reconnected with two spade terminals - it was a good job though, but it does beg the question - why?

The OE thermostat has been known to leak at the connector and when it does it pushes coolant up the wires which rots everything including the DME pins if it gets that far before being caught.

You might look at your DME pins and see if they have signs of coolant corrosion contamination.

Re: the Aux fan situation, it may be 'operating as designed'... the factory aux calibration does come on fairly high because indeed it's setup to kick in after the visco. That can be changed in software for the TU, but seems like its doing what its supposed to. The fan should not have to run at max jet-engine levels to keep your temps in check unless its over 100F outside. For reference I run ONLY the Aux fan so I have pretty good experience with what it should take...

I'd keep looking at T-stat, water pump, radiator... seems like something isn't actually getting the cooling done properly. E39 radiators aren't known for clogging so that'd be a rarity but again, something isn't getting rid of the heat like it is supposed to (the 'heater works to bring temps down' is a telltale...)