I switched to Mobil 1 at about 50 hours on my 25 Kohler. I honestly don't think it matters, but if you feel better change it to synthetic after a couple hundred.<p>BTW, you guys need to check your local Wal-Marts. About two months ago, ours had the 5 quart value jug of Mobil 1 for $14.97. Three bucks a quart is a pretty good deal. I bought about 10 of them and wish I had bought more. But I had heard of Wal-Mart selling them last year in other places, our store just got them this year and now they are gone.<br><p><font size="1">Edited by: Keith