Mercury Outboard Overheating
 

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.

I have only had the boat for a short while. The previous owner barely put 20
hours on it in 2 years. It was recently serviced by the previous owner as
well.

Any ideas?

Any way I can get hold of a workshop manual in digital format to pull down
and check the water pump?

Regards,

Mercury Outboard Overheating
 

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.

Mercury Outboard Overheating
 

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

-W

"Greg" wrote in message
...
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.

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

Mercury Outboard Overheating
 

Listen to Clams--sounds lean in mixture to me.

Mercury Outboard Overheating
 

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


"Greg" wrote in message
...
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.

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" wrote in message
...
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

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.

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" wrote in message
...
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.

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