Water cooling
An efficient, if expensive way to eliminate the need for most fans in ones computer
system is the implementation of water cooling devices. Water cooling kits
are available for beginners, and additional components or “water blocks” can be
added to the system, allowing virtually any system needing cooling to be put
“on water”.
Other cooling fluids are possible in a sealed system, although plain water is
generally preferred because it has higher heat capacity and thermal conductivity
than oil, and it is easier to clean up if a leak ever occurs: turn off the computer,
shake off most of the water, and use a hair dryer to evaporate the rest of the
water.

Oil cooling
Transformer oil has been used to cool electrical equipment for decades.
Some people are experimenting with oil cooling personal computers. Since
oil is non-conductive, the motherboard and graphics card and power supply
(but not the hard drives or optical drives!) will continue to run submerged in
a “fishtank” filled with oil. Some people prefer colorless transparent “mineral
oil” or cooking oil, but Frank Vlkel recommends motor oil.
Oil cooling is lower cost than water cooling, because it doesn’t require watertight
“blocks” or hoses. Some people leave the fans running on the motherboard
and power supply to “stir” the oil. Other people remove all the fans and add
a (submerged) pump to “blow” a stream of oil onto the CPU hot spot. Some
CPUs, if given a big enough metal heat sink, can be adequately cooled by passive
convection currents in the oil (and the large surface area of the oil-to-case and
case-to-air), without any fans or pumps.
If any cable (the hard drive ribbon cable, the power cable, the monitor cable,
etc.) exits the case below the oil line, it must have an oil-tight exit seal – consider
making all cables exit the top of the case instead.
Immersion in other cooling fluids has been attempted, such as fluorinert or
liquid nitrogen.