I looked at that manual and ordered the thermostat and gasket.....then went to install. Removed upper rad hose and it routes thru the hosing holding the generator and fan. Didn't take the housing right off but it doesn't appear to have a spot for the thermostat and there definitely isn't one in there now. I don't think there is a water pump on that engine???
Remove the "thermostat" housing that the upper radiator hose connects to. That's where the thermostat is located.
It's not too surprising to find some engines where the previous owner has removed the thermostat. Some people think if the engine operates in a warm climate a thermostat is not needed. But that is wrong - a thermostat helps warm up the engine quicker which reduces engine wear, and the thermostat provides some restriction to coolant flow (even when it is wide open) which helps in heat transfer.
I took it out and looked at the thermostat when I changed anti freeze and I think it had about 168* stamped on the thermostat which I have read that a diesel engine needs to run up to full temp. and never run a diesel (small eng.) cold. Maybe a 180 or 190 ,,,,I don't know. Thanks for the reply. My Isuzu has a water pump but I know some of the small Kubota's don't have a water pump. My cousin had one that was absent of a WP