The easy way to liquid cool things is to replace the heatsinks with blocks of plastic+metal and pump water through those. The plastic/metal things are blocky in

The easy way to liquid cool things is to replace the heatsinks with blocks of plastic+metal and pump water through those. The plastic/metal things are blocky in appearance so get called 'waterblocks'. That works because the hot bits of computers are fairly localised (GPU, GPU, maybe power delivery chips on the board) and the rest does fine with a little air movement. Flooding the board with oil means replacing components is messy and, at least historically, the oil slowly seeps into capacitors and kills them. So you're likely to cover the board in a thicker conformal coating / protective layer first which is also a pain. It's also not that effective, unless you have heatsinks on the hot parts anyway and try to force oil through them, maybe using pumps aimed vaguely at the heatsinks. I don't know the answer to the heater question. That's further from my old hobby.