Detecting and pinpointing fuel system leaks can be difficult and time consuming. Fuel being a fluid of light viscosity means that it can migrate quickly and mix with other fluids. This is especially true for fuel systems with components that are located inside an engine and hidden under covers. This means that finding these leaks and verifying repairs is very important to prevent repeat repairs and severe engine damage. Safety is also another consideration with regard to any fuel injection system and even more so with high pressure common rail fuel systems. Fuel spray under high pressure will easily penetrate human skin, even through many types of gloves and risking exposure must be avoided. Fuel injected into the skin can poison blood, cause flesh damage and infections resulting in removal of fingers and limbs or even cause death.
Adding ultra-violet tracer dye to fuel will help identify and pinpoint fuel leaks and help promote safety. Old-timers might recall a time when running a piece of cardboard or paper along fuel pumps, lines and injectors was a common method of locating leaks. Using dye and an ultra-violet lamp keeps your body at a safe distance during inspections.
Diagnostically speaking the use of tracer dye is by far superior than any other visual method because the dye is extremely visible even when a small leak is present. The following two photographs show two examples of tracer dye being used to diagnose fuel leaks on 6.4L Power Stroke diesel engines that have a high pressure common rail fuel system. In the first example a smaller, slow leak at the fuel inlet fitting that otherwise might not have been easy to find. The second example another injector is leaking at the upper body nut and is a fairly large leak that was fairly obvious to see with the naked eye yet difficult to be absolutely sure that it also was not just engine oil splashing off of the adjacent valve components.
To use, add one bottle of UV Tracer Dye to the fuel filter housing - secondary or engine mounted filter on multiple filter systems. Typically the bottles contain about 3-ounces and you need to be sure to use dye formulated for use with oil based fluids. NOT water based dyes (coolant) or refrigerant dye (air conditioning). Then prime the system and run the engine for about fie minutes to get the dye mixed with the fuel and circulating within the system. Shut the engine down and begin searching for external leaks with a UV lamp. For internal engine leaks access the components to be inspected then inspect with a UV lamp. On some engines with electric fuel pumps you may drain the engine oil and leave the drain plug out. Turn the fuel pump on with a scan tool capable of bi-directional control and wait to see fuel dripping from the crankcase. The presence of dye will simply confirm the fact that fuel is leaking... validating the need to access valve covers or pumps and continue inspecting. In some instances it may be necessary to run the engine while inspecting for leaks.