Gravely Commercial Pro Turn 260, 60 inch cut. It has a Kohler V-twin Model ECV749, 26.5 hp with 1,250 hours. I use it nearly everyday at work(thankfully have not had to sit in that old work truck at the gate lately) and it gets worked hard. I've been using 15W40 at 50-60 hr intervals with no problems, the one time I tried 20W50 it really did seem to lack power, so I've been using 15W40 since. We crank them up(we have two of them), let them idle for 2-3 minutes, then its full throttle till both fuel tanks run out, constantly bogging down in thick,wet grass shutting off the engines stopping in between. I looked up the oil specs for this engine, it shows 10W30 for 0 to 100 degrees, and straight 30 for 50 to 100 degrees. With 1,250 hrs on it, would it be safe to use straight 30, and would it maybe free up some power over the 15W40? Whatever I decide to go with, I'll start changing it at the recommended 100 hrs.
2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles