From the pics, it looks like a glow plug heater in a banjo fitting with a thermostat. I wonder what wattage is the heating element? I don't like it at all since the heat density must be very high. It'd be a lot cheaper and you'd get more gentle heating of the diesel fuel if you place a 1 foot section of 5/16 aluminum tubing along the upper radiator hose and wrap a towel around it for insulation and re-route the fuel line before the diesel fuel filter to the aluminum tubing.

Edit: It's a 200 watt heater, which is very close to what a glow plug puts out. It's $250!!!

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked