C30 Engine Overheating

The symptoms you describe do align with a potential fault in the active air flap system, particularly given the engine overheating and the check engine light. Have you performed a diagnostic scan to retrieve the specific fault code? It would significantly help narrow down the source of the problem.

A scan? I don't have anything to scan it with... Is that something I can easily do myself, or should I leave it to a pro?

While some basic OBDII scanners are available, interpreting the data accurately and understanding the implications for the active air flap system on your Volvo C30 often requires specialized knowledge. Given the potential for further engine damage due to overheating, I would strongly advise consulting a qualified technician for a proper diagnosis. The electromechanism of the flaps is often the culprit and the whole repair could set you back around 590€.

Thanks for the advice! You were spot on. Took it to the shop, they ran a diagnostic scan and confirmed it was the active air flap thingy. Ended up costing around that much, but at least it's fixed!