Mercury Outboard Overheating

 >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.

When you say overheating, do you mean the audible alarm comes on? Do you have a
guage that reads hot?
Does it have a water pressure guage? if so what is the pressure at this rpm?
The impellor should be changed yearly, so that a logical place to start.

More questions. What hull is the motor on?
I assume your hull is "mushing' at that speed. Not on plane, just moving a lot
of water.
Some boats were known to get hot running at those rpm's. The hull diverts the
water creating an air pocket allowing temps to rise.
You might try changing the trim angle and see what happens.

BR<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

Ya, I'd suspect a carb thing leaning it out.

-W

"Greg" <gfretwell.DeleteThis@aol.com> wrote in message
news:20040117112317.13646.00000117@mb-m27.aol.com...
 > Running lean?
 > You should probably throw an impeller at it if you don't know the status
of the
 > one you have. There are 5 bolts right near the cavitation plate, 4 down
and one
 > up from the bottom inthe back. That drops the foot. Then the impeller is
in a
 > small can around the shaft.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

Listen to Clams--sounds lean in mixture to me.
 >> Stay informed about: Mercury Outboard Overheating 

"Chunky" <rkirov RemoveThis @hotmail.com> wrote in message
news:4009051a$0$1744$5a62ac22@freenews.iinet.net.au...
 > 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<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

I drop the foot and check out the impeller as well as get the mixture looked
at.


"Greg" <gfretwell.RemoveThis@aol.com> wrote in message
news:20040117112317.13646.00000117@mb-m27.aol.com...
 > Running lean?
 > You should probably throw an impeller at it if you don't know the status
of the
 > one you have. There are 5 bolts right near the cavitation plate, 4 down
and one
 > up from the bottom inthe back. That drops the foot. Then the impeller is
in a
 > small can around the shaft.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

The temp guage goes way up into red. No alarm yet, I usually alter speed
before it gets too hot.

The funny thing is the range that it heats up on.

Just above idle its fine. A little faster and it heats up quick, then after
that if you get the speed up it cools off to normal. Thinking about it, what
could be happening is that at higher speed the ram effect is forcing water
thru the cooling system. Slow down and it relies on the pump which is not
performing optimally.

Regards,

"Boatriggr" <boatriggr.DeleteThis@aol.com> wrote in message
news:20040117123144.27163.00000197@mb-m11.aol.com...
  > >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.
 >
 > When you say overheating, do you mean the audible alarm comes on? Do you
have a
 > guage that reads hot?
 > Does it have a water pressure guage? if so what is the pressure at this
rpm?
 > The impellor should be changed yearly, so that a logical place to start.
 >
 > More questions. What hull is the motor on?
 > I assume your hull is "mushing' at that speed. Not on plane, just moving a
lot
 > of water.
 > Some boats were known to get hot running at those rpm's. The hull diverts
the
 > water creating an air pocket allowing temps to rise.
 > You might try changing the trim angle and see what happens.
 >
 > BR
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

That is why we all suggest thrwing an impeller at it. If this is new to you it
should be done anyway, just so you know where you are at but it might be your
whole problem. I have an example in my garage of a bad impeller that looks
perfect. The hub spins and that was RPM sensitive. It drove me crazy until I
just made up my mind to replace it.
A thermostat is also not a bad idea. They are cheap.
One thing you could try is have someone feel the discharge water when it says
it is hot. If the water is "MacDonalds coffee hot" you are overloading the
cooling system. (not enough water pumped, lean mix etc) If the water is cool
you probably have a sluggish thermostat. That is not likely if the engine runs
out good and then fails when you slow down. If it is a morning sickness problem
the thermostat is suspect.
 >> Stay informed about: Mercury Outboard Overheating 

Yeah I guess you are right, how do I get to the thermostat to check it?

Also is Mercury AF or Metric, in Australia I am used to metric? Dont want to
strip bolt heads.

I will drop the lower leg and chech the pump. One problem I foresee though,
is to get into the small hole above the trim tab to loosen the bolt, it is
damn deep and I am going to need some kind of thin extended socket to get to
it.

Thanks and regards,


"Greg" <gfretwell.DeleteThis@aol.com> wrote in message
news:20040118003105.11652.00000133@mb-m12.aol.com...
 > That is why we all suggest thrwing an impeller at it. If this is new to
you it
 > should be done anyway, just so you know where you are at but it might be
your
 > whole problem. I have an example in my garage of a bad impeller that looks
 > perfect. The hub spins and that was RPM sensitive. It drove me crazy until
I
 > just made up my mind to replace it.
 > A thermostat is also not a bad idea. They are cheap.
 > One thing you could try is have someone feel the discharge water when it
says
 > it is hot. If the water is "MacDonalds coffee hot" you are overloading the
 > cooling system. (not enough water pumped, lean mix etc) If the water is
cool
 > you probably have a sluggish thermostat. That is not likely if the engine
runs
 > out good and then fails when you slow down. If it is a morning sickness
problem
 > the thermostat is suspect.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

The foot bolts are American SAE, The powerhead may be metric if it is recent.
(They are swapping stuff with Yamaha)
I think the thermostat housing bolts are 10mm
 >> Stay informed about: Mercury Outboard Overheating 

 >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

Bill, just a warning, The metal hub impeller was the one I had that was
spinning. It is sourced from Sierra and they have (had?) a problem with the
bonding of the brass to rubber. It was RPM sensitive but I replaced it before I
had a well developed pattern. It wasn't until I actually had it in my hand that
I found the spun hub.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

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" <billgranbillgran DeleteThis @cfl.rr.com> wrote in message
news:4HrOb.16542$Bj.14109@twister.tampabay.rr.com...
 >
 > "Chunky" <rkirov DeleteThis @hotmail.com> wrote in message
 > news:4009051a$0$1744$5a62ac22@freenews.iinet.net.au...
  > > 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
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

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" <rkirov DeleteThis @hotmail.com> wrote in message
news:400e36df$0$1751$5a62ac22@freenews.iinet.net.au...
 > Well I changed the impeller although the old one was in good shape anyway.
 > Both have a brass hub.
 >
 > Checked the thermostats and the pressure relief valve and they are seem
 > fine.
 >
 > Ran the boat again today again same thing. Idle no problem. Bring up a few
 > revs to get 5 or 6 knots and the temp goes to the red zone. Open the
 > throttle a little more and still the same until the RPM is about 2000 and
 > the temp drops. Crank it up to 20 knots + and the temp drops to 150F and
all
 > is well.
 >
 > One thing I noticed is that the tell tale is more of a dribble now at low
 > speeds, and hot.
 >
 >
 >
 > "Billgran" <billgranbillgran DeleteThis @cfl.rr.com> wrote in message
 > news:4HrOb.16542$Bj.14109@twister.tampabay.rr.com...
  > >
  > > "Chunky" <rkirov DeleteThis @hotmail.com> wrote in message
  > > news:4009051a$0$1744$5a62ac22@freenews.iinet.net.au...
   > > > 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
  > >
  > >
 >
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

Are you sure your impellor is spinning?

Alan

"Chunky" <rkirov.RemoveThis@hotmail.com> wrote in message
news:400e36df$0$1751$5a62ac22@freenews.iinet.net.au...
 > Well I changed the impeller although the old one was in good shape anyway.
 > Both have a brass hub.
 >
 > Checked the thermostats and the pressure relief valve and they are seem
 > fine.
 >
 > Ran the boat again today again same thing. Idle no problem. Bring up a few
 > revs to get 5 or 6 knots and the temp goes to the red zone. Open the
 > throttle a little more and still the same until the RPM is about 2000 and
 > the temp drops. Crank it up to 20 knots + and the temp drops to 150F and
all
 > is well.
 >
 > One thing I noticed is that the tell tale is more of a dribble now at low
 > speeds, and hot.
 >
 >
 >
 > "Billgran" <billgranbillgran.RemoveThis@cfl.rr.com> wrote in message
 > news:4HrOb.16542$Bj.14109@twister.tampabay.rr.com...
  > >
  > > "Chunky" <rkirov.RemoveThis@hotmail.com> wrote in message
  > > news:4009051a$0$1744$5a62ac22@freenews.iinet.net.au...
   > > > 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
  > >
  > >
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating