boiling points than water, oils can be raised to considerably higher temperatures (above 100 degrees Celsius) without introducing high pressures within the container or loop system in question. Many oils have uses encompassing heat transfer, lubrication, pressure transfer (hydraulic fluids), sometimes even fuel, or several such functions at once. Mineral oils serve as both coolants and lubricants in many mechanical gears. Some vegetable oils, e.g. castor oil are also used. Due to their high boiling points, mineral oils are used in portable electric radiator-style space heaters in residential applications, and in closed-loop systems for industrial process heating and cooling. Mineral oil is often used in submerged PC systems as it is non-conductive and therefore won't short circuit or damage any parts. Polyphenyl ether oils are suitable for applications needing high temperature stability, very low volatility, inherent lubricity, and/or radiation resistance. Perfluoropolyether oils are their more chemically inert variant. A eutectic mixture of diphenyl ether (73.5%) and biphenyl (26.5%) is used for its wide temperature range and stability to 400°C. Polychlorinated biphenyls and polychlorinated terphenyls were used in heat transfer applications, favored due to their low flammability, chemical resistance, hydrophobicity, and favorable electrical properties, but are now phased out due to their toxicity and bioaccumulation. Silicone oils and fluorocarbon oils (like fluorinert) are favored for their wide range of operating temperatures. However their high cost limits their applications. Transformer oil is used for cooling and additional electric insulation of high-power electric transformers. Mineral oils are usually used. Silicone oils are employed for special applications. Polychlorinated biphenyls were commonly used in old equipment, which now can possess risk of contamination. Fuels are frequently used as coolants for engines. A cold fuel flows over some parts of the engine, absorbing its waste heat and being preheated before combustion. Kerosene and other jet fuels frequently serve in this role in aviation engines. Liquid hydrogen is used to cool nozzles of rocket engines. Waterless coolant is used as an alternative to conventional water and ethylene glycol coolants. With higher boiling points than water (around 370F), the cooling technology resists boil over. The liquid also prevents corrosion. Freons were frequently used for immersive cooling of e.g. electronics. Molten metals and salts Liquid fusible alloys can be used as coolants in applications where high temperature stability is required, e.g. some fast breeder nuclear reactors. Sodium (in sodium cooled fast reactors) or sodium-potassium alloy NaK are frequently used;