BMW M2 Cold Start & Overheating: Thermostat Mystery

Hey there! I had almost the exact same issue with my 2018 BMW M4 last winter. The symptoms matched perfectly, slow warm-up, cold running engine, terrible fuel economy, and sketchy heating. Also dealt with that annoying check engine light coming on and off. Took it to my trusted workshop and, yep, it was a faulty map thermostat. The whole job, including parts and labor, set me back about 350 Euro. Since getting it fixed, the car's been running like a charm, proper temperature, normal fuel consumption, and toasty cabin heat. Before I share more specifics, could you tell me your current mileage and if you've noticed any coolant loss? Also, are you getting any specific error codes with that check engine light? This would help confirm if we're dealing with the same issue. Hope this helps! Let me know those details and I can share more about my experience with the repair.

Thanks for sharing your experience! My M2 is at 70908 KM and was last serviced about 2 months ago. Haven't noticed any coolant loss, but I'm getting the P0128 error code consistently now. Your symptoms sound exactly like what I'm experiencing. Good to know the thermostat replacement sorted it out for you. Was thinking it might be something more serious (and expensive!). Did you notice any warning signs before the thermostat completely failed? I'm wondering if I should get this sorted right away or if I can drive it for another week or two.

Hey again! Thanks for those details. I can definitely help with your questions about the thermostat. So with my M4, looking back, there were some subtle signs before it completely went south. Started with slightly longer warm-up times, maybe an extra minute or two, but it gradually got worse over about three weeks. The P0128 code is exactly what I got too, which is pretty much the smoking gun for thermostat issues in these engines. About driving it for a week or two, honestly, I'd get it sorted sooner rather than later. While I did drive mine for about a week after noticing the issues (bad decision in hindsight), it's really not worth the risk. The constant cold running can affect your engine's efficiency and could lead to increased wear. Plus, you're just burning extra fuel for no good reason. The repair itself was pretty straightforward at the workshop, took them about 3 hours. Just make sure they use the right spec BMW thermostat. They actually showed me my old one after, it was stuck partially open, which explained all those symptoms. Since you've got the same symptoms and error code I had, I'd say you're definitely looking at the thermostat. Better to fix it now than wait for potential complications.

Thanks so much for the detailed response! You've really put my mind at ease about this. Think I'll call the workshop tomorrow morning and get it booked in ASAP, definitely don't want to risk any engine wear or keep wasting fuel. Really appreciate you sharing your experience, especially about how the symptoms progressed. Better to sort it now than regret it later. Good call on making sure they use the proper BMW thermostat too, I'll definitely mention that when I book it in. Thanks again for all your help with this!