Some 2003-2007 Ford F-Super Duty 250-750 vehicles built on or before 9-30-2008 and equipped with the 6.0L diesel engine may exhibit diesel fuel in the engine coolant, due to leaks in the cylinder head fuel injector area. Symptoms may include fuel in the coolant and coolant expulsion from the degas bottle.
Inspect the degas bottle for evidence of fuel in the coolant (not oil or combustion gases). If diesel fuel is present, follow these steps:
1. Drain coolant from the cooling system. NOTE: Failure to drain the cooling system prior to pressurization will result in an inability to diagnose the leak source, and will prevent bubbles from forming when sprayed with a soap and water solution.
2. Remove all fuel injectors from both cylinder heads.
3. Wipe the injector bores clean of oil and fuel.
4. Fit the cooling system pressure tester. Do not add coolant.
5. Apply 10 psi of air pressure to the sealed cooling system. It is suggested to use a hand operated pressure tester or regulated shop air with a tee in the degas bottle hose.
6. Spray a 50/50 mixture of dish soap and water generously inside each injector bore. Ensure that the cylinder head injector bore casting is coated with a soap layer.
7. Inspect each injector bore for bubbles. A light and mirror or bore scope may aid in pinpointing a leak location. The most common area is between the two injector fuel sealing O-rings in the sealing area on the side nearest the cylinder glow plug.
8. Replace the cylinder head if a leak through the casting is found. Be sure to flush the entire cooling system.