BMW Z3 Cooling Nightmares: Thermostat or Something Worse?

Hey there! I had similar issues with my 2004 BMW Z4 last winter (I'd say I have some experience working on BMWs, including my old 325i). The symptoms you're describing sound exactly like what I dealt with. My car was taking ages to reach operating temperature, fuel consumption went through the roof, and the heating was terrible. Took it to my trusted workshop and, yep, it was a faulty map thermostat. The whole repair, including parts and labor, cost me around 350 Euro. The mechanic explained that the thermostat was stuck partially open, causing all these issues. Once replaced, everything went back to normal, proper heating, normal fuel consumption, and stable engine temps. Could you share your engine type and mileage? That would help me give you more specific advice since different BMW engines from that era have slightly different cooling system setups.

Thanks for sharing your experience! I've got the gasoline engine version with 6912 KM on the clock, just had it serviced recently. Really good to hear it was just the thermostat in your case and not something more serious. Did you notice any immediate improvement in the engine temperature after the repair? Also, did they recommend replacing anything else while they were working on the cooling system? I'm hoping it's the same straightforward fix for mine.

Hey again! Yeah, with my Z4 the improvement was literally immediate after the thermostat replacement. The moment I started the car after the repair, I could tell the difference. The temperature gauge started climbing normally, and the cabin heat was properly toasty within minutes, such a relief! Actually, since they had the cooling system open, my mechanic suggested replacing the coolant and doing a thorough system flush while they were at it. Made sense to me, and I'm glad I did it. The coolant in these BMWs should be changed periodically anyway, so it was good timing. With your mileage being relatively low, I'd say you're probably looking at the same issue I had. These map-controlled thermostats are known to act up sometimes, regardless of mileage. One thing though, make sure they check the electrical connector on the thermostat too. In my case, it was a bit corroded, and they cleaned it up during the repair. After the fix, my fuel consumption dropped back to normal within the first tank. The engine's been running at perfect temperature ever since. If you're having the exact same symptoms as I did, I'd bet money it's your thermostat too. Just make sure you get a quality replacement part, I learned that lesson the hard way with my old 325i!

Thanks so much for all the detailed info! It's really reassuring to hear your fix was so straightforward and made such an immediate difference. I'll definitely take your advice about the coolant flush and checking the electrical connector, might as well do it all while they're in there. Really appreciate you mentioning about getting quality parts too, definitely don't want to cheap out and have to do this twice! I'm gonna call my mechanic tomorrow and schedule this in. You've saved me a lot of worry, was starting to think it might be something way more serious. Really appreciate you taking the time to share your experience!