V70 Overheating and Coolant Leak

Sounds like a connectivity issue. When you say 'overheats', is it gradual or sudden? Does it happen at idle, or only under load? The symptoms point to a possible control module malfunction. Have you checked the CAN bus connections? A defective cable or plug connection of the component may be the cause.

The overheating seems to happen more when I'm driving for a while, not so much when idling. I haven't checked the CAN bus – what exactly am I looking for?

Alright, more likely control unit is the culprit then. The CAN bus is the car's internal communication network. You'd be checking the wiring and connectors for any signs of damage, corrosion, or loose connections. But honestly, with those symptoms, and unless you're very comfortable with vehicle electrics, it's probably best to get it to a workshop, they'll have the tools to diagnose the specific control unit causing the issue.

Thanks for the advice. Took it to the shop, and they found a defective plug connection. After that it was a quick fix, cost me 95€, now the Volvo is running smoothly again!