FAN-A/C 3608353 - Caterpillar

3304 And 3306 DI Engines With New Scroll Fuel SystemsThe manual bleed valve is no longer used on the above engines. The fuel return to tank orifice that was a part of this valve is now a part of the fuel gallery cover in the fuel injection pump housing. Formerly, it was possible to overtighten the manual bleed valve and cause it to have a leak.
If it becomes necessary to bleed a fuel system that does not have the manual bleed valve, a different method must be used. Small amounts of air that get into the fuel system during filter changes will bleed through the fuel return orifice. If a large amount of air must be removed from the system, loosen the fitting at the pump housing cover where the fuel returns to the tank. Use the starter to turn the engine until clean fuel comes out of the outlet for the fitting, or use the hand priming pump if equipped. Tighten the fitting.
If equipped, always use the hand priming pump to fill new fuel filters.
If the engine runs out of fuel, or if there is any reason to bleed the fuel system at the high pressure fuel injection lines, see the respective Service Manual for the correct procedure.