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berndwolf76

BMW 4 Series Overheating + No Heat: Bypass Valve Issue?

Fault stored

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Overheating

Hey all, having trouble with my 2017 BMW 4 series. Engine's overheating and the cabin heat isn't working. Got an error code stored too. I suspect it might be a bypass valve issue but want to confirm before taking it to the shop. Has anyone dealt with similar symptoms? What was the actual problem and how did your mechanic fix it? Looking for real experiences here.

4 comment(s)


MNoack88

Hey there! I have some experience working on BMWs and had a similar issue with my 2015 BMW 3 series. When I encountered those exact symptoms, it turned out the water pump had failed earlier, and that caused damage to the thermostat housing. The dealership fixed it under warranty since the water pump failure was the root cause. They replaced both parts at no cost to me. Before you go to the shop, could you share: Current mileage? What's the specific error code? Notice any coolant leaks or low coolant warnings? This info would help determine if you're facing the same problem I had. BMW 4 and 3 series share a lot of cooling system components, so I might be able to give you more specific advice.

berndwolf76 (Author)

Thanks for offering to help! I'm currently at 81104 KM and just had my service done not too long ago. The error code I'm getting is P0128. Haven't noticed any puddles under the car, but the coolant level has been dropping slowly over the past few weeks. The temperature gauge started acting up about two days ago. Really hoping it's not as serious as what you experienced with your 3 series, but those symptoms sound pretty similar to what I'm dealing with.

MNoack88

Hey again! Thanks for providing those details. Your symptoms are eerily similar to what I experienced with my BMW 3 series. That P0128 code (thermostat too cool) was exactly what I got before things got worse. The slow coolant loss you're mentioning is what really catches my attention here, that's how mine started too. I initially thought it was just normal consumption, but it turned out to be the early warning sign of the water pump starting to fail. The temperature gauge acting up was the final red flag that got me to the dealership. Since you mentioned your service was recent, did they check the cooling system thoroughly? In my case, even after regular service, the issue wasn't caught until it became more obvious. I'd strongly recommend getting it checked soon, better safe than sorry. When my water pump failed, it cost way less to fix than if I had waited and ended up with a damaged thermostat housing like in my previous case. Have you noticed any sweet smell from the engine bay? That was another symptom I remember from my experience, though I didn't connect it to the problem at first.

berndwolf76 (Author)

Thanks so much for all that info, it's actually super helpful and a bit concerning at the same time. No, I haven't noticed any sweet smell, but I'm definitely going to check for that now. You've convinced me to take this more seriously than I initially planned. I called my regular mechanic and booked it in for tomorrow morning. After what you've shared about your experience, I don't want to risk waiting and ending up with more extensive damage. Really glad I asked here first, your water pump situation is making me think this could be more than just the bypass valve I initially suspected. During my recent service they did a basic cooling system check, but I don't think it was super thorough. Guess that's how they missed the early signs. I'll make sure to mention your experience with the water pump to my mechanic, could save them some diagnostic time. Just one last thing, do you remember roughly how long it took to fix when you got it sorted? Need to plan my work schedule around this. Thanks again for all your help, really appreciate you sharing your experience!

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