BMW Diesel Temperature Issues, Cooling Grille Suspect

Hey there! I've got some experience working on BMWs and had a similar issue with my 2015 BMW 3 Series diesel. I think I know what you're dealing with. I had almost identical symptoms on mine, erratic temp readings, CEL, and slow warm-up times. After taking it to my regular workshop, turned out it was just a blown fuse connected to the cooling system control module. Pretty simple fix actually, cost me 52 Euro including labor. But before jumping to conclusions, could you tell me if you're getting any specific error codes? Also, how long has this been happening, and have you noticed any coolant loss? This info would help me give you better advice based on my experience. Just a tip, if you've got a BMW 2 series, it's worth checking the fuse box first. Could save you some time and money.

Thanks for your detailed response! Mine's at 27908 KM from the latest service, and I'm not seeing any coolant loss so far. I actually checked the fuses already but they all seem fine. I'm getting error code P0128 (coolant temperature below thermostat regulating temperature). Haven't spotted any visible leaks or other obvious issues. Really appreciate the suggestion though, wish it was that straightforward in my case!

Yeah, I hear you about wishing it was just a fuse! After you mentioned the P0128 code, it reminded me that I actually had that same code pop up again on my 3 Series about 6 months after the fuse incident. Turned out my thermostat was failing, it wasn't opening and closing properly. Definitely explains the wonky temperature readings and slow warm-up you're experiencing. Since you're at 27908 KM since your last service and getting the same code I had, I'd bet money it's your thermostat. When mine went bad, I initially thought it was the cooling grille too, but nope! The replacement thermostat cost me around 180 bucks plus labor. Not the cheapest fix, but once it was done, all those symptoms cleared right up. Quick question, have you noticed if your heating isn't as warm as it used to be? That was another telltale sign I experienced with my thermostat issue. Either way, might be worth getting that thermostat checked out since our symptoms are matching up so closely.

Thanks so much for sharing your experience, that's super helpful! You're right about the heating actually, now that you mention it. I have noticed it's not as toasty as it used to be, especially during cold starts. Really sounds like we're dealing with the same thermostat issue here. Guess I should stop overthinking the cooling grille angle and focus on getting the thermostat checked out instead. I'll ring up my workshop tomorrow and mention the P0128 code and thermostat suspicion. At least now I've got a better idea of what I'm potentially looking at cost-wise. 180 plus labor isn't too bad considering all the headaches this has been causing. Thanks again for walking me through your experience, it's definitely given me more confidence about what to expect when I take it in!