Ethan K,
I also would recommend using the IH/Kohler recommended Straight SAE 30 Weight oil. I've used several different kinds of oil over the years, the last I consistently used was 15w-40 diesel oil (I have 3 diesel vehicles in the fleet and usually had this on-hand). This spring, due to a sale at one of my local outlets, I was able to get 3 cases of Shell brand oil for $40. I bought 2 cases of Straight 30 Weight and a case of 2-cycle oil. Did my spring oil changes with this Straight 30 Weight and have seen my oil consumption go down, drastically. I mow 2 properties, my yard, that is about .3 acre and one that is at least 2 acres. Last year, I would need to add a "glug" of oil to be back to the full mark after mowing my yard. After mowing the large property, I would be down to the "add" mark. This year, running the 30 weight, I see no change in the oil level after mowing my yard, and only need to add the "glug" after the large property. I've yet to be down to the "add" mark this year.