BMW 6 Diesel Cold Start Issues: Bad Glow Plugs?

Hey there! I had something very similar with my 2015 BMW 5 series diesel. I've got some experience working on cars, but nothing too advanced, mostly basic maintenance stuff. Last winter, my 520d started acting up exactly like yours, preheating light staying on and really rough cold starts. Since I also own a 3 series, I initially thought it was just the cold weather, but it got worse. Took it to my regular workshop and they diagnosed a faulty glow plug, ended up costing me 440 Euro to fix. The mechanic showed me the old plug, and it was completely shot. Once replaced, the car started like a dream again, and the battery stopped struggling during start-up. Can you tell me which engine variant you've got in your 6 series? Also, have you noticed any other warning lights or symptoms? This would help me share more specific details about my experience that might be relevant to your case.

Thanks for sharing your experience! I've got the 640d model with 145415 KM on it. My last service was about 3 months ago, but this issue started recently. Really appreciate the insight about the glow plug, that's particularly helpful since our symptoms seem identical. Mine's also struggling more during these cold starts, and I'm definitely noticing the battery taking a bigger hit than usual. Haven't spotted any other warning lights yet, but that preheating light is stubborn and won't go away. Sounds like I might be looking at a similar repair bill as yours. At least it's not something more serious!

Hey again! Thanks for confirming those details about your 640d. After hearing more about your situation, I'm even more convinced we dealt with the same issue. You know what's interesting? When I got mine fixed, my mechanic mentioned that the 640d uses pretty much the same glow plug system as my old 520d. One thing I didn't mention in my first reply, before I got mine fixed, I noticed the problem would get worse after the car sat unused for a couple of days. Kinda sounds like what you're experiencing. The fact that yours has similar mileage to what mine had when it failed (I was around 150k when it happened) makes me think even more that we're dealing with the same problem. Just curious, does your car take a few extra cranks to start when it's been sitting for a while? Mine did that too, and it completely went away after the glow plug replacement. The price might sting a bit, but honestly, it's worth getting it sorted before it potentially causes any other issues. Plus, winter's not the time you want to be dealing with starting problems! Let me know how it goes if you get it checked out. Always interested to hear if my experience matches up with others!

Thanks so much for the follow-up! Yes, you've described my situation perfectly, especially about those extra cranks after the car sits for a while. Mine definitely struggles more if I don't use it for a day or two. It's really reassuring to hear that fixing the glow plug solved all these issues for you. I've actually just booked an appointment with my mechanic for next week. It's annoying to deal with the repair cost, but you're absolutely right about getting it sorted quickly. I'd rather not risk any additional problems, and these cold starts are getting pretty frustrating. I'll update you once I get it checked out, really appreciate all your help and shared experience with this! Seems like we BMW diesel owners need to stick together when it comes to these quirks!