I suppose it is the old diesel engine technology. My 1700 does not burn any oil, very good compression and power, noting wrong with head gaskit, no mixing of anti-freeze and oil and yet after 5 to 6 hrs engine oil gets dark. Now, I use Rotella for engine oil and not NH brand and saying that never had any issues either. I also change and filter faster than I should at every 50 hrs. Conversely, I use kubota oil for my MX-4700 and at first 50 hr of service the oil looked pristine to the point I saved it in a gallon jug and just use it for my oiler thingy and oil up joints and stuff with. I think it is the oil but more so engine technology.