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.