I have a 2002 4 stroke 60 HP Merc.
I took it in for the 500 hr and everything was fine before I took it in. $437
later (a new impeller, plugs and an oil change) I have an overheating problem
when I go over 4000 RPM.
I get Mercury involved and they say go to another dealer. $350 later (lots of
easter egging around, a new thermostat, a housing THEY BROKE and another
impeller) and I am still overheating. I hooked up a guage and it is 4PSI
until
the thermostat opens then it is more like 2PSI. RPMs don't seem to change it
much and whenever I get much over 3000 RPM I see the temp climbing. At 4000
it
is very hot and the beeper goes off.
I am collecting a white pasty substance around the thermostat that I think is
a
result of evaporating salt water since the flow is so low. Even when it is
all
flushed out I am still having the problem.


I know you have been around boats a while.
While this can be tricky to trace, basic troubleshooting should steer you to a
solution.
One thing I would ask is: Was the engine overheated?
I have seen the grommet where the water tube goes into the powerhead adapter
melt. That would limit the flow to the powerhead.
When they changed the impeller did they change all the gaskets?


BR