My vote goes for: pump all the oil through a giant radiator which is cooled by a diverted river (or leave the cold tap on full and don't tell the water company!)
I was interested in how they dealt with the hard drives, which traditionally don't play well with submersion due to having breathing holes to equalise pressure inside and outside the drive.
Seems like they just wrapped them in a sleeve to block off the holes? I'm not sure that'll work too well.. all the modding projects I've seen do this either used SSDs, mounted the hard drives out of the oil, or provided pipes out of the oil attached to the breathing holes.
I seem to remember oil even got into a drive via the power/sata connectors too, which doesn't bode well. Good luck to them anyhow.