Excursion Overheating Control Module Error

Sounds like a possible CAN bus communication issue, which could definitely cause those symptoms. Overheating and coolant issues along with a CEL can point to a sensor malfunction or miscommunication. Have you tried scanning for any specific diagnostic trouble codes (DTCs)? The fact that it's overheating makes me think a sensor reading might be off, causing the fans not to kick on properly, or the engine to run lean. Do you have access to a car diagnostics tool? It would be useful to check the data link connector, and if there is any corrosion on the wiring.

I do have a basic OBD2 scanner. It's throwing a generic 'control module communication error'. Nothing specific beyond that. You mentioned CAN bus. Could a bad connection somewhere really cause all these problems? Where should I even begin looking for a faulty connection?

A bad connection in the CAN bus or any of the control module wiring could cause those problems, yes. The modules need to talk to each other. A break in communication can manifest in bizarre ways. However, without specific codes, it is a gamble. Given the symptoms and generic code, and considering it's an older vehicle, the most likely cause is a defective cable or plug connection. At this point, I'd suggest taking it to a workshop. They have the proper tools to perform a more in-depth car diagnostics.

Thanks for the input! Dropped it off at the shop. Turns out, it was indeed a corroded connector on one of the control modules, causing all sorts of miscommunication. They cleaned it up and replaced a short section of wiring. Total cost: 95€. Runs like a champ now.