BMW 7 Series Thermostat Woes: Hot Then Cold Symptoms

I had nearly identical issues with my 2015 BMW 5 Series last season. The symptoms matched yours exactly, inconsistent temperature readings, slow cabin heat, and higher fuel consumption. Turned out it was indeed a faulty map thermostat. Got it fixed at the garage, and the mechanic showed me the old thermostat, it was stuck partially open, causing all those temperature regulation problems. The repair was straightforward but getting to the thermostat was a bit tricky since it's buried deep in the engine bay. Took about 4-5 hours of labor. This isn't just a minor inconvenience, running with a bad thermostat can lead to engine damage if left unchecked. After the replacement, my car's been running perfectly, normal temperature readings, quick cabin heat, and fuel consumption back to normal. If you're seeing these symptoms, I'd recommend getting it checked soon. The longer you wait, the more strain you're putting on your engine.

Thanks for sharing your experience! That's really helpful, especially since our symptoms match up so closely. It's good to know fixing the thermostat sorted everything out for you. I'm curious, do you remember roughly how much you ended up paying for the whole repair? Also, has everything been running smoothly since then, or did you notice any other issues pop up afterward? Thanks again for the detailed info!

Hey there! Happy to help with more details about my BMW 5 repair. The whole thing actually cost me 350 € to fix, mainly for the defective map thermostat replacement. I'd say it was money well spent! Since the repair, I haven't had a single temperature-related issue. The mechanic spotted that the Thermostat cooling circuit motor was defective and fixed that too during the same visit. Let me tell you, what a difference! The car's running like a dream now, heats up normally, maintains steady temperature, and my fuel consumption is back to where it should be. The cabin warms up super quick too, which is a massive improvement from before. Really glad I got it sorted when I did, the mechanic mentioned waiting longer could've caused some serious engine problems. If you're still on the fence about getting it checked, I'd say go for it. These symptoms are classic thermostat failure signs, and it's better to fix it sooner rather than later.

Thanks everyone for the advice! Wanted to give you all an update on my BMW situation. Finally got the courage to visit a new mechanic, and boy, am I glad I did! The guy was super professional and spotted the issue right away, faulty thermostat, just as suspected. Repair bill came to about 400 €, a bit more than expected, but they found and fixed a small coolant leak too. The whole job took about 5 hours. Got to say, watching them work was pretty interesting. They really knew their stuff, especially with BMWs. The difference is incredible! Car's running like new, temperature gauge stays steady, cabin heats up quickly, and my fuel consumption has dropped back to normal. Such a relief to have this sorted. Definitely learned my lesson about not putting off these kinds of repairs. Thanks again for pushing me to get it checked out. Sometimes you just need that extra nudge to make the right decision!