"God Bless, the dumb and the stupid because they know,not what they say."

Aside from the irony, I say to him...show me "plenty of inboards" using
radiators.

One of the many reasons that we don't comonly see radiators on inboard boats
is that
a normally sized radiator would fail to sufficiently cool the engine. In an
automotive or truck applicaton, a portion
of the engine cooling is accomplished by air moving across the block and heads
as the vehicle travels down the highway. In some extreme cases, engines with
enough fins attached to sufficiently increase the surface area exposed to the
moving air can be air cooled. No such conditions exist in an engine
room.....(we hope!)