Ending my third season with my FasTrak 20/52 Honda and will be doing my first IZT Oil and Filter change. The manual calls for 20w-50 oil. I read a post a while back where someone used Mobil 1 15w-50 synthetic in the FasTrak IZT's and reported a 15 degree f. lower operating temperature. I'd like to the get the longest life out of this machine and would this Mobil 1 route be recommended? I mow two acres once a week during the growing season and mulch a ton of maple leaves in the fall. About 3/4's of an acre that I mow is on a pretty steep slope and that is where my concern is as to not overheat the IZT's. This machine has performed flawlessly thus far in three seasons and want it to stay that way.