Having worked in aviation with piston engines and turbine engines, it has been for the longivity of piston engines to allow the engines to normalize from the extra heat generated in the working operation RPM by letting the lubricants (oil) disapate the built up heat from working and allowing the oil to disapate the extra heat. On Kubato ZTR Z331 manual suggests allowing engine to cool down for 2 minutes at a fast idle before shutting down. Allison Turbines learned the lesson years ago from bearing failures due to synthetic oil breakdown causing oil restrictions in the oil jets causing lack of lube to bearings. We had to cool down a full 2 minutes before shutting down. The oil temps would drop almost a 150 degress in that time. Makes sense to allow a piston engine the same previlage and adds to a longer lasting engine and transmission.
Cecil Jackson
Gravely 300 (2001 850 hours)
Kubota Z331 (2012 128 hours)
mowing 6 acres