Electric Fuel line heaters are used in place of Coolant/Fuel heat exchangers to bring VO/PO temperature up and lower viscosity prior to the VO filter (in most cases). In some cases 12vdc inline fuel heaters are used in place of Coolant/fuel heat exchangers but this often places such a high demand on onboard electrical production that a larger capacity alternator must be installed. On some electric fuel heaters an option exists to set a desired fuel temperature..other have a non-adjustable maximum temperature.
Two types of 12volt electric fuel heaters exist:
Immersed Element (glowplug) type heaters
Heated Tube type heaters.