Good evening.I replaced fuel injection valves with water cooling on auxilliary engine. After 1 hour of work of diesel engine I found spots of fuel in cooling water expansion tank. I tested fuel valves no leakage from cooling holes on fuel valves.How to check if no leakage fuel to cooling system when overhauling fuel injection valve.

Hello pavloandriyanov. What grade of fuel are you using and at what temperature? Were the valves replaced with OEM spares and were they new or reconditioned? It seems that the DK20 doesn't have a dedicated nozzle cooling system but is cooled with water from the JCW and I can't see how it gets from the head into the valve body or nozzle, there also seems to be a system where the JCW cools the external side of the nozzle which I cannot figure out either. However, the only place I can think of where nozzle water would meet fuel is at the face between the body and the nozzle, hence the question about the replacement valves. You could try plugging the spill line from the valve in the test rig to prevent recirculation and apply all the pressure, just below the opening pressure, to the seals and see if anything leaks out. The valve in the engine is a different world to that of the test rig so this is why you may not be picking up a leak on the rig. Are there any other symptoms e.g. fuel leak-off tank filling up? How about shutting the engine down on gas oil, fuel off and supply and spill disconnected from the valve; will the static head of the JCW push water out of the fuel line? Maybe the lower viscosity water will find a way out. Good luck, John