BMW Z4 Overheating Mystery: Coolant Leak and Limp Mode

Hey there! I have some experience working on BMWs. I went through something similar with my 2006 BMW 325i (also had a 330i before). The symptoms you're describing sound exactly like what I dealt with. Mine had a faulty cable connection to the coolant temperature sensor, which was causing incorrect readings and making the system go haywire. The ECU was getting wrong signals, hence the limp mode and warning lights. Took it to my regular workshop and they diagnosed it pretty quickly. They found the connector was corroded and the wiring was damaged. Total fix was about 95 Euro, mostly labor costs since they had to trace the wiring and replace the connector. Before we dig deeper, can you tell me if you've noticed any other electrical issues? Also, have you checked if the coolant temperature gauge shows normal readings when you first start the car? This info would help narrow down if you're facing the same issue.

Thanks for sharing your experience! My Z4 is showing very similar symptoms to what you described. Currently at 175759 KM and just had a service last month, but these issues started popping up recently. The coolant temp gauge actually does act weird on startup, it jumps around a bit before settling. Haven't noticed any other electrical issues though, everything else seems to work fine. Maybe it's really just the sensor connection like in your case. That's a relief to hear it might not be something major. I'll definitely have them check the wiring and connector when I take it in. Was worried it might be something way more expensive! Did you notice any improvement in overall performance after your repair?

Hey again! Glad to hear back from you about your Z4. Yes, after fixing that connector issue on my 325i, there was a noticeable improvement in how the car ran. The engine temperature stayed consistently normal, and the unusual limp mode episodes completely stopped. It was like getting a new car! The sporty feel came right back, and I could finally push it without worrying about those warning lights popping up. The symptoms you're describing with the temp gauge jumping around at startup, that's exactly what mine was doing. It's a classic sign of a dodgy connection or sensor issue. These BMWs are pretty sensitive when it comes to their electrical systems. Just thought I'd mention, after my repair, I started checking the connectors regularly during service intervals. These things can get dirty or corroded over time, especially with all those KMs on the clock. Your mileage is pretty close to what mine was when I had the issue (mine was around 168000 KM). Keep us posted on what your mechanic finds. I've got a feeling it'll be something similar to what I dealt with. These issues can be scary when they first pop up, but they're usually not as bad as they seem!

Thanks so much for all the detailed info! You've really put my mind at ease about this whole situation. It's great to hear from someone who's dealt with almost the exact same problem. I've booked the car in for tomorrow morning, and I'll definitely have them check those connections and sensors first. You're right about these BMWs being sensitive, learned that the hard way! But honestly, when they're running right, they're just amazing to drive. I'll make sure to ask them about regular connector checks during future services too. That's a really good tip about preventive maintenance. Never thought about how those connectors could get gunked up over time. I'll update this thread once I get the diagnosis. Fingers crossed it's just a connector issue like yours was. Really appreciate you taking the time to share your experience, it's super helpful when dealing with these quirky issues!