I just changed the oil in the Walker, was already running Amsoil 5w-40, switch to Amsoils 15w-40 heavy duty marine diesel & gasoline 12 tbn oil. What a difference in the operating temperature of the 20hp Kohler air cooled engine. Their is a 150 degree cooler temperature difference in the cylinder head temp, thats confirmed with a lazer temperature gauge after several passes over a zyoshia yard today. When I lifted the hopper up on the Walker, the engine compartment is noticably cooler with the 15w-40 oil. Kohler recommeds a 5w-30 or 10w-30?