If you have an old PSU, I would open it, and see which parts have heatsinks on them. You can assume that these might need cooling. After that run the PC with the opened PSU and the fan disabled. If the PSU is open, I doubt if it will get damaged due to high temps. After it has been running for a while (30 mins should be fine) shutdown, remove the power cable and touch all of the components. By doing this You will know what gets hot and what doesnt. As far as I know the only hot parts are the voltage regulators and the transformer. I took a pic of them in case you don't recognize them.
I hope this helped you out
Warning: This isn't something to be taken lightly.
Please be careful when opening up power supplies. Capacitors can store electricity for very long periods of time. (That is a capacitor's job after all) Even long after being unplugged. I don't mean to sound like a fraidy cat, but these things carry potentially deadly amounts of electricity.
If you don't properly remove the stored charge in these caps you could electrocute yourself.
Yeah, touching things on the ps is a little concerning. What would happen if the ps fan
was turned off altogether? Anyway i think that
maybe a metal jacket could be made for the transformer! this should be fool proof.
Only the death of the pump would bring the end
of days. hehehe