BMW M4 Overheating + No Heat: Bypass Valve Alert

Hey there! I faced nearly identical issues with my 2019 BMW M2 last year. The symptoms you're describing are eerily similar to what I experienced, it turned out my water pump had failed, which then caused the thermostat to malfunction as a consequential issue. Initially, I thought it was just the thermostat, but when my mechanic dug deeper, they found the water pump was the root cause. It's actually a common issue in these engines. The pump failure means no proper coolant circulation, hence your hot engine and no heat in the cabin. Got it all sorted at a specialty BMW shop. While it was a serious repair that needed immediate attention (to avoid potential engine damage), it wasn't something unique or extremely complicated for them. Since both parts were connected in the failure chain, they replaced both the pump and thermostat, plus did a complete coolant system flush. My advice? Don't risk it with a general mechanic. Get it to a BMW specialist, these cooling system issues need proper diagnostic tools and expertise.

Hey, thanks for sharing your experience! That's really helpful as it sounds exactly like what I'm dealing with. I had a feeling it might be the water pump/thermostat combo but wasn't entirely sure. Would you mind sharing roughly how much you ended up paying for the whole repair? Also, just curious, has everything been running smoothly since the fix, or have you noticed any other related issues pop up? These BMWs can be tricky beasts sometimes, so I'd love to know what to expect. Thanks again!

Hey again! Just wanted to update you, your post actually reminded me to mention something important. While my initial repair did include the water pump and thermostat, the mechanic actually found that the bypass valve was malfunctioning too. The best part? Since it was a consequential error from the original water pump failure, they fixed it at no extra charge! Everything's been running like a dream since then, no overheating, perfect cabin heat, and all warning lights stayed off. It's been about 15 months now with absolutely zero issues. My total bill was around 1,200 for the pump and thermostat work, but like I said, the bypass valve fix was covered as part of the related repair work. These BMWs definitely keep us on our toes, but once you get the cooling system sorted properly, they're pretty solid. Just make sure you get it checked out soon, you definitely don't want to risk any engine damage by waiting too long. Hope this helps with what you're dealing with!

Thanks for the detailed follow-up! I actually just got back from the mechanic today. You were spot on about everything, it was indeed the water pump causing all the trouble. Got it sorted at a specialist BMW shop, and they found the same cascade of issues you mentioned. What a relief to have it fixed properly! The bill came to about 1,300, which seems fair considering the work involved. They did a thorough job, replacing the pump, thermostat, and checking all the connected systems. The mechanic was super professional and even showed me the worn-out parts to explain what went wrong. The car's running beautifully now, temperature's perfect, heater's working great, and that annoying warning light is finally gone. Really glad I asked here first instead of going to my old mechanic. Sometimes paying a bit more for the right expertise is totally worth it. Thanks again for your help, you saved me from potentially making a costly mistake with a general mechanic!