inconsitent? ive only recommended 2 oils 10w30 and sae30, based on climate, except command/valves! I know what i know, like it or not! and you will NOT find 15w40 in an engine manual! Go waste your money on amsoil etc, think of it as an insurance policy! Point is, these engines have ran on 10w30/sae30 for years, and unless you have a TRUE commercial piece, 9x out of 10 the engine is going to outlast the machiene regardless of what oil you use!! definatetly when your asking about low end equipment such as this! now you brought up the kohler engine thats OLD, whats the chance it had some high dollar modern syn oil in it? NONE, yet its still going, im not a know it all, but have yrs upon yrs of experience, and i HATE seeing ppl waste $ on stuff they dont need/high $ oil!