7.3 with leaking radiator overflow reservoir

A customer brought in his Ford 7.3 Super Duty with diesel fuel in his cooling system. He had previously replaced his injector cups, but they were installed improperly. The correct tool to install the injector cups was not used, therefore the cups did not seat correctly. However, injector cups can crack and leak over time with normal wear and tear in any diesel engine. The cups were letting diesel fuel and coolant mix. Since the fuel system has a higher pressure than the cooling system the fuel was feeding into the radiator and it's reservoirs. The excess fluids were leaking out. This causes your fuel mileage to nose dive and over time can soften all the rubber surfaces in the engine. On this job we had to replace the o rings on the thermostat, water pump seals and all the engine hoses. If not discovered in time it can also damage the radiator seals.

When the engine is shut off the cooling system pressure exceeds that of the fuel system and water can seep into your fuel filters and fuel tank. The water can cause rust and corrosion in the entire fuel system. For this customer we also replaced the fuel filters, drained and cleaned the fuel tank.

In the top left picture you can see part of a rubber seal that was being sucked into the injector.

In the top right picture you can see the fuel and water mixture inside the injector.

In the 2 above pictures you can see the fluid dripping into the injector cup (while the engine is running)

In this video clip the leak looks like a shadow moving across the top left section of the injector cup.
It's actually coolant dripping through the crack and into the injector cup.
It's easiest to see in full screen mode.