On Wed, 6 Jan 2010 18:13:12 -0800, "mgg" wrote:

In the case of a boat, cooled with very cold raw water, the thermostat may
(and does) actually close while running to get the temp back up. Your engine
may seem to run fine without it, but you'll get better fuel economy and
performance with it.

And longer engine life also. Running cold increases friction and
wear.