You guys all make good points about oil, I do tend to over analyze things somewhat.:smile: I guess as long as you maintain a mower properly it will last a long time. I have an old 1975 Dodge trk. thats been in the family since new and we always have run 10w40 in it so I always have some laying around. 10w40 has a lot of vis. index improvers in it, well most dino oil do, thats where synthetics have an advantage because they need less or so ive been told. I do think conventional oils are closing the performance gap somewhat. Synthetics are still very much better, I use them also but dino oils have served me well so far.