BMW i8 Hybrid Cooling System Nightmare: Help Needed!

Hey there! I have some experience working on hybrids and dealt with a very similar issue on my 2019 BMW i3. The symptoms you're describing sound exactly like what I faced. My car showed the same problems, slow warm-up, high fuel consumption, heating issues, and that annoying check engine light. After taking it to my trusted mechanic, it turned out to be a faulty map thermostat. The repair, including parts and labor, cost me about 350 Euro, but it completely solved the problem. Before you move forward, could you share: Does the temperature gauge show consistent readings? Any specific error codes when the CEL comes on? Have you noticed any coolant leaks? This will help confirm if you're dealing with the same issue I had. The i8 and i3 share similar cooling system designs, so I might be able to provide more specific insights.

Thanks for sharing your i3 experience! I have my i8 at 84076 KM and just did my service last month. The temp gauge fluctuates between normal and slightly elevated, especially on longer drives. Already checked for coolant leaks but found nothing obvious. The CEL usually shows P0128 when it pops up. Starting to think it's definitely the thermostat like in your case. Do you remember how long the repair took? Also, did you experience any hesitation during acceleration while you had this issue? Just trying to confirm if all symptoms match up before I book an appointment with my mechanic.

Hey again! Yes, those symptoms definitely match what I experienced with my i3. The P0128 code is exactly what I got too, it's pretty much a dead giveaway for thermostat issues in these BMWs. The repair took about 3-4 hours at my mechanic's shop. And yes, I actually did notice some hesitation during acceleration while I had the problem, something I forgot to mention in my first reply. The engine management system gets a bit confused with the incorrect temperature readings, which affects performance. Since you mentioned your mileage is around 84K, it's right in the range where these thermostats typically start acting up. Mine failed at about 78K, so the timing makes sense. The repair completely resolved all the issues, proper warm-up time, normal fuel consumption, and no more hesitation during acceleration. Quick tip from my experience: make sure they also check the coolant level sensor while they're in there. Mine was showing signs of wear, so I had them replace it at the same time. Saved me from potentially having another issue down the road. Just be prepared that the i8 parts might cost a bit more than what I paid for my i3, but the labor time should be similar. Let me know how it goes once you get it fixed!

Thanks so much for all the detailed info! Really helpful to hear about the timing being similar, makes me feel better about my diagnosis. I'll definitely get them to check that coolant level sensor too, smart thinking. Just booked an appointment for next week. They quoted me around 500 for parts and labor, which sounds reasonable considering it's an i8. Funny enough, right after I read your reply about the acceleration hesitation, I paid more attention during my drive home and noticed it's definitely there, especially when merging onto highways. At least I know I'm not imagining things! I'll post an update after the repair to help others who might run into the same issue. Really appreciate you taking the time to share your experience, saved me a lot of worry and diagnostic guesswork.