Why does my vintage movie projector keep overheating during classic film nights?

I recently dug up an old 16mm movie projector from my grandparents' attic to recreate those cozy classic film nights. It’s a Bell & Howell from the 1950s, and I've lovingly cleaned it up, replaced the bulb with an LED alternative, and even tried using different reels. But every time I watch a film longer than 30 minutes, the projector starts to heat up and eventually shuts off, killing the vibe. I’m running it in a small, ventilated room, and I’m double-checking that the vents aren’t blocked. I want to keep the vintage charm alive but also avoid frying the motor or bulb. Has anyone else dealt with overheating vintage projectors or similar old tech? Would adding a small external fan or cooling setup be a good idea, or could that cause other problems? Also, are there specific maintenance tricks to keep these old machines running cool and smooth during longer watch sessions?