991 Overheating: Coolant Valve Mystery Needs Expert Fix

Hey there! I had a similar issue with my 2015 Porsche Cayman S last summer. The symptoms were exactly what you're describing, engine temperature climbing and the CEL coming on. Turned out to be the coolant bypass valve cable connection that had come loose and was causing improper coolant flow regulation. Took it to my Porsche dealer in town, and they diagnosed it pretty quickly. The fix involved replacing the entire bypass valve assembly since the connection point had worn out. It wasn't a majorly serious issue, but definitely not something you want to ignore since it can lead to engine overheating if left unchecked. From my garage experience, the repair was straightforward but required specific Porsche diagnostic tools to properly reset the system. The whole thing took about a day to fix, and they also did a full coolant system inspection while they were at it. If I were you, I'd definitely take it to a certified Porsche dealer or a specialized Porsche workshop for this one. It's not worth risking further damage with a general mechanic who might not be familiar with the specifics of the 991's cooling system. Hope this helps!

Thanks for sharing your experience! That sounds exactly like what I'm dealing with. Can I ask how much the repair ended up costing you? And have you had any other cooling system issues since they fixed it? Just trying to get an idea of what I'm in for here.

Hey again! Happy to give you an update! After taking your advice, I got my Cayman S checked out at the Porsche dealer, and you were spot on, it was definitely the coolant bypass valve. The total bill came to 155€ for fixing the cable connection that was acting up. Pretty reasonable, considering it was a dealer service. And here's the good news, since getting it fixed last summer, I haven't had a single issue with the cooling system. The car's running like a dream, no more check engine lights or temperature problems. It's like night and day difference! Honestly, I'm really glad I didn't try to cut corners with a general mechanic. The Porsche guys knew exactly what they were looking for and sorted it out properly. Money well spent, if you ask me. Hope this helps with your decision! Let us know how it goes with yours.

Thanks so much for all the details! I actually just got back from the Porsche dealer myself. You guys were totally right about going to a specialist. They found the same issue, coolant bypass valve acting up, and fixed it right away. Cost me about 180€ in total, but honestly, it was worth every penny. The whole experience was way better than my last mechanic. The dealer's team was super professional, explained everything clearly, and had me in and out in a day. Car's running perfectly now, no more check engine light, and the temperature gauge is staying exactly where it should be. Really appreciate everyone's help on this one. Sometimes it pays to just bite the bullet and go to the experts. Guess I've found my new go-to mechanic! Take care, everyone!