ASCII.jp has been immersing computing devices in canola oil, because I guess mineral oil is too safe or something. While the article is not very receptive to automatic translation, from what I gather, they've already toasted a couple devices. This time, they took an ECS LIVA Core to the dunk tank and filled it with about four liters of said canola oil, which is about a US gallon.
Again, if you're looking to do oil cooling yourself, just use mineral oil.
Image Credit: ASCII.jp
The PC was passively cooled, using just the circulation caused by currents of relatively warm oil. I say relatively warm, because the Core M has a single-digit expected wattage. They allowed OCCT to run for eight hours, which yielded a stable temperature of about 44C in a 24C room. Again, this is without pumps or radiators or anything like that. The only difference between this and passive air cooling is how effective oil is at absorbing heat, in speed and capacity, compared to air. That said, air is a fairly good insulator, so that should imply that oil has a better chance.