You may have given us a clue, with the low psi. Where did you take the
reading? top of the block? before or after the thermostat? Also, what is
your water source? Are you using the clamp on "ears" or is the foot
submerged? I'm not sure of the spec for your particular motor (my 200hp 2
stroke climbs up to 10-15 psi at idle and 20-25 at 4-5000rpms) but some
motors are half that. No matter, 2-4 psi taken properly at 2000-4000rpm
sounds way too low. Assuming the impeller is correct and installed
correctly, something in the line is leaking and preventing pressure from
building.

On another note, Are the new plugs of the same heat range? A "hotter" plug
could be the culprit.
LD

"Greg" wrote in message
...
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.