I am searching for some free knowledge here. I have not ever performed a compression test on a diesel before. I have had numerous marine diesels and when I needed to work on them for compression problems, there was no question, they needed a total overhaul. I have placed oil in the cylinders during compression tests on spark induced engines to help differentiate ring ailments from valve seat ailments and understand the process. My problem is this: On diesels, how does one differentiate between valve seat problems and rings? If I inject oil in the cylinders of my diesel the little gem will burn the test medium and fire up for a ride. Would someone please explain if there is another test to isolate compression loss and how it works? Thanks in advance for your help.