I've got a 2012 335is with 56k miles on it. Recently I noticed that my oil temp gauge bounces around by about +/- 5 degrees (all within a 2-5 second period). The average temperature reflects what I would expect, but it jumps around. That by itself would not be a big deal but as the temp gets to about 240-250 degrees, the cooling fan engages at maximum speed (and sound) for about 5 seconds, and then shuts off. Then every 15-30 seconds the on/off process repeats. During my last trip to the dealer (still under CPO warranty) the dealer found nothing wrong with the system - "normal operation". No error codes. No issues. Really? I've put my Autoenginuity scanner on it and it does confirm that the temperature from the oil temp sensor jumps around exactly as the dashboard gauge shows (nice to see that the gauge really mirrors the raw data). Can the true oil temperature really move by 5-10 degrees within a few seconds? What happened to thermal mass? Based on what I can see, the cooling fan seems to follow what the DME tells it to do. It turns on at about 220 degrees coolant temp, and turns on with the AC regardless of the temperature. When it cycles and spins up to full speed I think it's because it's told to do so and not because it's failing in some way. I can also initiate a full speed fan run with the scan tool and it follows it as directed. Before I replace the oil sensor and drop $200 on the part, I wanted to see if this behavior is in fact normal (temp jumping around and fan cycling like that). If it is not, is it typical for the sensor to fail and result in those symptoms? Obviously if I can convince the dealer of the problem that would be a bonus, but at this point I'm more concerned about proper cooling system operation, especially as we are heading into the Arizona summer.
Charlson will have more specific insight, but - are you still on the original battery? That might be worth a check, it seems the modern BMW's that use the battery registration procedure can suffer all manner of inexplicable wonkiness once the battery starts to fade. I have a 335is too, '11 model (5/10 production - 7 yrs old now!), manual, 49k. Nice car, like mine a lot. Those turbos on the N54, it'll get up n' scoot!
Good question on the freshness of the battery. I had a cursory look but of course all the relevant tags are covered up by the distribution panel. I would think it's not the original battery as most of them don't last that long in our climate. The battery voltage seems solid and I don't have any startup issues. The alternator voltage seems nice and steady. I also give the battery an occasional full charge. The boosted N54 is amazing. I'm a big fan of the manuals but after driving the DCT I'm almost a convert. I felt like I was letting the full potential of the engine down due to my human-speed gear shifts. Of course I can't bring myself to sell my 6MT ZHP so perhaps I'm a full convert just yet.
One quick update. I noticed that the fan cycles at high speed even when the engine is not warmed up yet but I am driving around (oil temp gauge at min). It just does not do that while not at temp and idling in the garage.
Update: Based on additional observations, although the oil temp jumps around a bit I don't think it is in any way responsible for the erratic fan issues. Some literature out there states that there is no link between oil temp and fan activity. My observations support this since even with cold oil the fan activity is present. I first noticed the fan issue as the ambient temperature rose and I started to use the A/C. Having the A/C compressor running causes the fan to start operating at about 20-30% of power to create air flow on the condenser. This creates a fan speed base from which the speed increases to the point where it gets very noisy. So perhaps the erratic requests were always there but since the fan never went to full speed where it is easy to hear, I never noticed it. Since driving is required for this to manifest, I have no good way of observing this. I've also confirmed that the ECU does not request high fan speed when the car is sitting at idle (or even with high revs while parked). However, the moment I start driving (if the A/C is on), all I hear is the fan cycling every 15 seconds between max speed and some other not so noisy speed. Is this normal? I looked at all the other temp sensors for the coolant and they all have steady outputs. I looked at the PWM pulse going to the fan controller and the fan seems to follow exactly what the ECU tells it to do. Does the fan speed request respond to turbo boost since it only manifests itself while driving? Seems like bad design if it cycles for such short intervals. Can anyone confirm if they have similar behavior on a 335is? That over-sized 600W fan certainly adds to the noise it can generate.
I haven't noticed this on my car - if it's happening, I'm not hearing it, but if it's that noisy, I presume I'd likely notice it.
Thanks MGarrison for the feedback. I'd like to report that the problem has been identified and fixed! The culprit was the coolant pump. Once I excluded the oil temp sensor as the source of the problem, there were some similar posts on other forums pointing to either the coolant pump or the A/C pressure sensor. The A/C pressure sensor came up clean. Here is also a video of my diagnostics showing that the pump was working fine and the coolant temperature was in range. However, that was while parked in the garage and no symptoms from the fan: https://1drv.ms/v/s!AoucqsA-hzHVg99m7WoEE9btCC4XvQ - normal operation As soon as I would start driving, the fan would start cycling. Then a few days ago the fan was going nuts while I pulled into my garage. This is when I captured this video: https://1drv.ms/v/s!AoucqsA-hzHVg99qIeCF7ljZfC-uyA - now the fan cycles Here you can see the water pump going on/off and once the pump goes to full speed the fan spools up to full speed (you can hear it in the background). While pulling its 600W you can see the supply voltage drop, then the pump shuts off and then the process repeats. Not surprisingly at some point the DME did throw the 2E81 error code for cooling pump speed deviation. I'm surprised it took this long given this must have been going on for quite some time. Got the pump replaced today under CPO warranty. So far so good. The only item that I'm still monitoring is a loss of power issue that I recently got on up-shifts from 2nd to 3rd under moderate acceleration in manual shift mode. Once 3rd gear engaged I had loss of power for about 2-3 seconds. I suspect that if the up-shift happened at the exact moment that the system was cratering, the DME was saying "Nein" to the throttle request. Hope this is the end of this story.
Thx for the update, glad you got it figured out - sounds like your coolant pump was calling it quits right on schedule, as it seems the E9x electric pumps are approx. +/-60k, reportedly. I better think about replacing mine!
