I have looked into running synthetic oil in the Duetz and have not done it yet. A 4 wheeler mechanic told me once that some synthetics turn into a product that has to be chiseled out of the oil pan if they ever get too hot. Keep in mind this is in an air cooled 4 wheeler that was probably left idling on a hot day with no air movement around the cylinder. Regular oils did not do that. Second reservation I had about the synthetics is I am a firm believer in changing engine oil at least once a year in a combine and cannot stand to leave dirty oil in engine over the winter. This practice drives up the cost of synthetics because the oil is so expensive (4-8 times regular oil). Your oil consumption gets expensive with synthetics, also. Now having said all of that, there is no doubt that synthetics will do a much better job lubricating that engine and can handle more heat. I would be picky about which synthetic I dropped in there. Merry Christmas Kelly