I get up close to 180+ but never tripped the alarm so far.

I have a suspicion the popper or bypass as you call it is the problem. The
spring is too strong and not opening soon enough.

If you left it out I guess it would make the motor run too cool at low RPMs.

Regards,

"Bill Sc" wrote in message
. ..

I have the same problem on a merc 225. Goes up to 175 deg at 1200 rpm
(about 6-8 knots) and is o.k. above and below that rpm. I suspect the
bypass (relief) valve is not opening soon enough. I never get into the
red
zone and never set off the audible overtemp alarm so I have been living
with
it for 10 years with no problem.

I have been tempted to drill a hole thru the bypass disc but haven't done
it
yet. Might make the engine idle too cold.

A lot of people without temp gauges probably have the same problem and
don't
even know it.

"Chunky" wrote in message
u...
Well I changed the impeller although the old one was in good shape
anyway.
Both have a brass hub.

Checked the thermostats and the pressure relief valve and they are seem
fine.

Ran the boat again today again same thing. Idle no problem. Bring up a
few
revs to get 5 or 6 knots and the temp goes to the red zone. Open the
throttle a little more and still the same until the RPM is about 2000
and
the temp drops. Crank it up to 20 knots + and the temp drops to 150F and
all
is well.

One thing I noticed is that the tell tale is more of a dribble now at
low
speeds, and hot.



"Billgran" wrote in message
. ..

"Chunky" wrote in message
u...
My 1995 Mercury 135HP 2 StrokeOutboard has decided to overheat
whenever
the
RPMS are around 1200-2000. Either side it cools off but in this
range
it
warms up fast. The water pump is working because it streams water
ok.
Nothing seems to be bloking the intake.




Assuming that the thermostats are operational and the pressure relief
valve
on the side is not sticking, then you may need the heavy duty impeller
that
Merc sells, but it is not the one included in their water pump kits.
The
following is an excerpt from a friend who "chased" a similar problem
on
his
V6 Merc for quite a while.

"As for my intermittent overheating problem, we finally cured it --
but
I
had
to call an engineer at Mercury for the magic bullet. It was my
starboard
engine that was overheating at displacement speeds
(approx. 1200-1800 rpm),

The Merc guy said to substitute what he called the "standard"
nylon-hub
water pump impeller (Merc #47-89984T-3) that came with the rebuild kit
(#46-96148A) with the "heavy duty" brass-hub impeller (#47-89984T-4).
It's
the same impeller, just different hub materials. He couldn't explain
why,
but said it usually works with problems like I was having. Son of a
gun,
he
was right. I switched them out and the problem is gone. Hallelujah."

Hope that this could be of help to you.

Bill Grannis
service manager