"Stephen Trapani" wrote in message
...
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

If your engine is fresh water cooled then the best operating temperature is
about 180 degrees. You can even go higher if the FW system is pressurised
with the sort of pressure cap you find on cars.
However, if it is salt water colled anything over 130/140 degrees is too hot
as it will bring deposits out of the salt water that will block the cooling
passages.
I do not think it is a good idea to regulate temperature by throttling back
the salt water system by partially closing the inlet valve as the pump is
most probably a rubber vane type positive displacement pump and this will
shorten the impeller life.
If FW cooled there should be a thermostat on the FW side that takes care of
the temperature.
If SW cooled the way to go is to fit a bypass around the pump with a valve
it so that excess water can be passed back to the suction side of the pump
and does not go through the engine.. Adjust the valve to bypass the right
amount of water to give the correct temperature in the engine.
To work this system properly you need a temperature gauge on the engine
since it is important not to go above about 140 degrees.