A while back I had a guy put a temperature gauge on my Yanmar. I thought
he installed it incorrectly until last weekend. A guy loaned me this
slick hand held temperature laser gauge thing which he said to aim at
the thermostat body for the running temperature of the motor. It read
115. The installed gauge starts at 120. Once I shut off the motor I
switched the key back on and it read about 135 on the installed gauge.
Must have warmed up once the water wasn't running through it. So the
installed gauge works, but the motor pretty much never gets up to 120.
And I mean never, when it's running, even when I have it full throttle,
pushing the boat along for hours!

So my question is this: A nearby very experienced boat refurbisher guy
with alot of Yanmar experience said I should decrease the flow in the
raw water sea cock until the temp reads 140-160. He said some diesel
motors use this method (Perkins I think he said). He said I shouldn't
mess with the thermostat because it was easier to just decrease the
water flow through the sea cock. This won't hurt the water pump? I
asked. No, he said.

So, good idea? Is it a big deal to keep the motor running warmer? Bad
idea to decrease the flow through the ball valve sea cock? What do you
all think?

Stephen