72fj here,i have a 04/gmc c6500 in my shop with engine oil in cooling system.installed new oil cooler cor about 8 months ago,truck has been working good last wheek came back with oil in cooling system r&r oil cooler and psi checked core ok.i have heard that injector coppers could be the prob but dont know witch way to go on this one any info would be app thank you 72fj. this engine is the inline six diesel

 

hmmm, inline six

are you getting massive ammounts of pressure in the coolng system?

 

cooling system not getting pressurized by cylinders or blown head gasket.pressurized the cooling system no coolant in crank case.

 

run it to operating temps and keep it pressureized, could only be leaking when its warm