I think the field rep was smokin' something, its the same engine with a bigger bore and the heads are a little bit different. all the internal parts except the pistons are interchangeable with the 18 and 20's, I do not doubt someone had heating issues but its not from the design.
golf coarse equipment of all kinds run the 23hp in completely enclosed compartments. a lot of idling and low RPM's for hours at a time.
just going off of what I work on daily is all