[C320-list] Overheating Problem

[Scott Thompson]

The temps sound too low for the alarm to be going off.  Maybe you have a 
  bad overheat sensor, or maybe the gauge is reading too low.

Do you have good water flow out of the muffler when this is happening? 
I've sometimes had problems when first running after the winter when 
there has been a slightly loose hose connection on the input side of the 
raw water pump.  This can cause the pump to suck some air instead of 
water and reduce efficiency, especially at lower RPMs.  (Same can happen 
with a worn impeller, even if no blades have broken off, but obviously 
that isn't your problem with a new impeller.)  Finally, make sure the 
intake strainer isn't clogged.

Rick Onyshko wrote:
> I have a 3 year old Yanmar 3YGM and had an overheat alarm go off on my first trip after the winter.  I replaced the impeller, no missing vanes.  It seemed to run at normal temp ~ 150 for over an hour.  Today I took it out and had it idling while I dropped sails and put fenders out, and it did not overheat but the temp went up to about 170.  Returned to 150 when I started moving forward and the RPM went up.
>  
>  Not sure if anyone has any ideas or suggestions, it has typically run right at 150 pretty consistently.  
>  
>  Thanks
>  
>  Rick