Mercury Outboard Overheating

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" <billsp655(nospam)@tampabay.rr.com> wrote in message
news:6PwPb.37236$Bj.34405@twister.tampabay.rr.com...
 >
 > 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.TakeThisOut@hotmail.com> wrote in message
 > news:400e36df$0$1751$5a62ac22@freenews.iinet.net.au...
  > > Well I changed the impeller although the old one was in good shape
anyway.
  > > Both have a brass hub.
  > >
  > > Checked the thermostats and the pressure relief valve and they are seem
  > > fine.
  > >
  > > Ran the boat again today again same thing. Idle no problem. Bring up a
few
  > > revs to get 5 or 6 knots and the temp goes to the red zone. Open the
  > > throttle a little more and still the same until the RPM is about 2000
and
  > > the temp drops. Crank it up to 20 knots + and the temp drops to 150F and
 > all
  > > is well.
  > >
  > > One thing I noticed is that the tell tale is more of a dribble now at
low
  > > speeds, and hot.
  > >
  > >
  > >
  > > "Billgran" <billgranbillgran.TakeThisOut@cfl.rr.com> wrote in message
  > > news:4HrOb.16542$Bj.14109@twister.tampabay.rr.com...
   > > >
   > > > "Chunky" <rkirov.TakeThisOut@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 

yeah i spoke to a couple of mechanics. One suggested drilling a 1/8" hole in
each of the thermostats to allow some extra water to run thru the system
until the poppet opens at 2000RPM. I have drilled a couple of holes as
described and will put it in the water tomorrow. It makes a lot of sense
because whenever the motor gets hot all i do is open the throttle and the
temp drops like a rock.

Regards,

Kind of makes sense
"Boatriggr" <boatriggr.DeleteThis@aol.com> wrote in message
news:20040121174833.04580.00000384@mb-m10.aol.com...
  > >
  > >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.
 >
   > >>>>>>>>>>>>>>>>>>>>>>
 >
 > Did you ever reply as to what hull it is on?
 > Did you try changing the trim angle?
 >
 > A cooling system can be tricky as there a a few instances where removing
the
 > powerhead becomes necessary to check some things.
 > If you are not sure of what is going on it sounds like time to take it to
 > someone with experience.
 >
 > BR<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

Well the saga continues:-

Drilled the holes, no difference.

Took out the thermostats completely, still no difference.

The mechanics I spoke to were stumped. Now I was getting really suspicious
of the whole overheating thing. Bought a multimeter and a digital
thermometer. I noticed while using the multimeter that one of the
rectifer/regulators (what takes care of the power coming off the alternater
to charge batteries, ignition, accessaries etc.) was looking scorched. I
examined it further and realised it was burnt out. So the electric system
was limping along on 20 amps instead of 40. Ordered a new regulator.

I also checked the temperature sender with the multimeter to see how it
registered. I checked the ohms it out put along with the table that converts
this to temperature. I also put the sender into very hot water along with
the digital thermometer. The temperature guage in the cockpit matched the
sender and the digital thermometer. Hmmm! So the guage was right and the
sender.

I then glued the digital thermometer between the cylinder head and exhaust
manifold near the send and took the boat out. The temp guage worked up to
200+ °F and then I checked the digital thermometer which showed 171 °F.
Tried a few times heating up the engine and checking the temp, 167, 156 etc.
So the guage reads high by 30-40° but it checked out ok when I compared it
on the beach.

I now suspect the loss of one regulator is causing the guage to read high
when the engine is running. When the engine is running fast the temp appears
to go down when in actual fact the motor is simply generating more power.



"Chunky" <rkirov DeleteThis @hotmail.com> wrote in message
news:400f65b1$0$1723$5a62ac22@freenews.iinet.net.au...
 > yeah i spoke to a couple of mechanics. One suggested drilling a 1/8" hole
in
 > each of the thermostats to allow some extra water to run thru the system
 > until the poppet opens at 2000RPM. I have drilled a couple of holes as
 > described and will put it in the water tomorrow. It makes a lot of sense
 > because whenever the motor gets hot all i do is open the throttle and the
 > temp drops like a rock.
 >
 > Regards,
 >
 > Kind of makes sense
 > "Boatriggr" <boatriggr DeleteThis @aol.com> wrote in message
 > news:20040121174833.04580.00000384@mb-m10.aol.com...
   > > >
   > > >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.
  > >
   > > >>>>>>>>>>>>>>>>>>>>>>
  > >
  > > Did you ever reply as to what hull it is on?
  > > Did you try changing the trim angle?
  > >
  > > A cooling system can be tricky as there a a few instances where removing
 > the
  > > powerhead becomes necessary to check some things.
  > > If you are not sure of what is going on it sounds like time to take it
to
  > > someone with experience.
  > >
  > > BR
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating 

I am following this closely as I have the identical problem. Please post
results when you install the new rectifier.



"Chunky" <rkirov.TakeThisOut@hotmail.com> wrote in message
news:4013afe3$0$1721$5a62ac22@freenews.iinet.net.au...
 > Well the saga continues:-
 >
 > Drilled the holes, no difference.
 >
 > Took out the thermostats completely, still no difference.
 >
 > The mechanics I spoke to were stumped. Now I was getting really suspicious
 > of the whole overheating thing. Bought a multimeter and a digital
 > thermometer. I noticed while using the multimeter that one of the
 > rectifer/regulators (what takes care of the power coming off the
alternater
 > to charge batteries, ignition, accessaries etc.) was looking scorched. I
 > examined it further and realised it was burnt out. So the electric system
 > was limping along on 20 amps instead of 40. Ordered a new regulator.
 >
 > I also checked the temperature sender with the multimeter to see how it
 > registered. I checked the ohms it out put along with the table that
converts
 > this to temperature. I also put the sender into very hot water along with
 > the digital thermometer. The temperature guage in the cockpit matched the
 > sender and the digital thermometer. Hmmm! So the guage was right and the
 > sender.
 >
 > I then glued the digital thermometer between the cylinder head and exhaust
 > manifold near the send and took the boat out. The temp guage worked up to
 > 200+ °F and then I checked the digital thermometer which showed 171 °F.
 > Tried a few times heating up the engine and checking the temp, 167, 156
etc.
 > So the guage reads high by 30-40° but it checked out ok when I compared it
 > on the beach.
 >
 > I now suspect the loss of one regulator is causing the guage to read high
 > when the engine is running. When the engine is running fast the temp
appears
 > to go down when in actual fact the motor is simply generating more power.
 >
 >
 >
 > "Chunky" <rkirov.TakeThisOut@hotmail.com> wrote in message
 > news:400f65b1$0$1723$5a62ac22@freenews.iinet.net.au...
  > > yeah i spoke to a couple of mechanics. One suggested drilling a 1/8"
hole
 > in
  > > each of the thermostats to allow some extra water to run thru the system
  > > until the poppet opens at 2000RPM. I have drilled a couple of holes as
  > > described and will put it in the water tomorrow. It makes a lot of sense
  > > because whenever the motor gets hot all i do is open the throttle and
the
  > > temp drops like a rock.
  > >
  > > Regards,
  > >
  > > Kind of makes sense
  > > "Boatriggr" <boatriggr.TakeThisOut@aol.com> wrote in message
  > > news:20040121174833.04580.00000384@mb-m10.aol.com...
   > > > >
   > > > >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.
   > > >
   > > > >>>>>>>>>>>>>>>>>>>>>>
   > > >
   > > > Did you ever reply as to what hull it is on?
   > > > Did you try changing the trim angle?
   > > >
   > > > A cooling system can be tricky as there a a few instances where
removing
  > > the
   > > > powerhead becomes necessary to check some things.
   > > > If you are not sure of what is going on it sounds like time to take it
 > to
   > > > someone with experience.
   > > >
   > > > BR
  > >
  > >
 >
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Mercury Outboard Overheating