Ive got a 2005 Cat D4 With a Mitsubishi 5mvxl05.0aae and I noticed oil pressure dropped and found alot of diesel in the oil.Changed oil and filter ran for 15 minutes and its already 1/4" higher and smells of diesel. I dont know wether its the injector orings?or i/p shaft seal..theres not really any blow by or smoke runs fine just loses oil pressure. its also the mechanically injected not the oil pressure injected style

 

Sounds like you have one or more injectors leaking fuel into the cylinders, you should also get a look at your rings.

 

Thats what i was also wondering but wouldn't I have more than normal blow by to have that much diesel getting past the rings?and some smoke? how to i determine where it coming from i don't want to pull the pump for it not to be the shaft seal either.I was thinking about trying some Uv dye in the fuel and pull the inspection plate in front of the i/p gear to see if its in there

 

well I rebuilt the injection pump an viola no more diesel getting into the engine oil and unit runs fine but i changed the oil and filter and the oil pressure is still reading almost zero at idle when it warms up,when cold its around 40psi...and i dont think it the gauge because the oil pressure light is also coming on and they each have their own sensors.someone mentioned theres a check valve in the oil cooler?