Spider Overheating Electric Fan

Overheating in a Spider isn't good. You're right to suspect the electric fan. Before jumping to conclusions, have you checked the fan's fuse and relay? Also, does the fan spin freely by hand when the engine is off? A seized motor could also cause overheating, even with a good electrical connection. Let me know what you find.

Good suggestion! I hadn't considered the fuse and relay. Where would I find the relay for the electric fan? And if it spins freely, what should I do next?

The relay is usually in the main fuse box, often under the bonnet or near the battery. Check your owner's manual. If the fan spins freely and the fuse/relay are good, the problem is likely the electric motor itself or the wiring harness. Considering potential engine damage, I'd recommend a workshop. A misdiagnosis could be catastrophic.

I checked with my multimeter and couldn't find anything. I brought it to a workshop, and you were right: a corroded plug caused a short circuit, preventing the fan from operating. They replaced the plug, and all is well. 95€ later, and the Spider is purring again. Thanks!