mercury force
 

mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for nothing
to come out the tell-tale for the first 2 or 3 minutes... the local dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy

mercury force
 

Andy C wrote:

mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for nothing
to come out the tell-tale for the first 2 or 3 minutes... the local dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy



I don't have the specific answer to your question, but consider this: On
the larger outboards I've owned, I've noticed it takes *under* a minute
for water to start exiting the powerhead. That was true for the Mercs
and is true for the Yamaha. Two or three minutes? That seems a long
time. While the outboard is running, its waterpump impeller is spinning
and pulling water up into the powerhead for cooling. There's no
auto-type radiator in an outboard, so where would all that water being
pumped up into the powerhead be stored?


--
Email sent to is never read.

mercury force
 

A lots of Mercs and Mercury-Force place the tattle-tale after the
thermostat. You can actually trace the hose to the back side of the
thermostat housing. With those setups the thermostat does have to open
before it will discharge a stream while idling. It should, though, discharge
some when you rev them while cold. The system is also pressure based which
should override the thermostat system.



"Andy C" wrote in message
...
mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy

mercury force
 

The flexable impeller allows water "blow by" until the thermostat opens.

-W

"Harry Krause" wrote in message
...
Andy C wrote:

mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local
dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy



I don't have the specific answer to your question, but consider this: On
the larger outboards I've owned, I've noticed it takes *under* a minute
for water to start exiting the powerhead. That was true for the Mercs
and is true for the Yamaha. Two or three minutes? That seems a long
time. While the outboard is running, its waterpump impeller is spinning
and pulling water up into the powerhead for cooling. There's no
auto-type radiator in an outboard, so where would all that water being
pumped up into the powerhead be stored?


--
Email sent to is never read.

mercury force
 

Clams Canino wrote:

The flexable impeller allows water "blow by" until the thermostat opens.

-W

"Harry Krause" wrote in message
...
Andy C wrote:

mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local
dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy



I don't have the specific answer to your question, but consider this: On
the larger outboards I've owned, I've noticed it takes *under* a minute
for water to start exiting the powerhead. That was true for the Mercs
and is true for the Yamaha. Two or three minutes? That seems a long
time. While the outboard is running, its waterpump impeller is spinning
and pulling water up into the powerhead for cooling. There's no
auto-type radiator in an outboard, so where would all that water being
pumped up into the powerhead be stored?


--
Email sent to is never read.




Aha! I didn't know that. Tanks!

--
Email sent to is never read.

mercury force
 

That seems a long
time. While the outboard is running, its waterpump impeller is spinning
and pulling water up into the powerhead for cooling. There's no
auto-type radiator in an outboard, so where would all that water being
pumped up into the powerhead be stored?

hi harry, there are other 'pee holes' in the gear unit before the water gets
to the powerhead, so the water can keep flowing regardless of whether it's
flowing through the powerhead or not...
andy

mercury force
 

thanks ken,
yes, the hose is on the back of the thermostat housing as described, so i
guess this is normal... i thought there would be some sort of bypass to keep
the telltale going all the time the engine is running
it just seems like a strange set up... presumably in very cold water the
thermostat could open and close constantly and you would not be able to tell
if the water pump was working or not...

It should, though, discharge
some when you rev them while cold. The system is also pressure based which
should override the thermostat system.

i don't quite follow that, are you saying the water pressure will force the
thermostat open above idle ?

thanks !
andy

"Ken" wrote in message
...
A lots of Mercs and Mercury-Force place the tattle-tale after the
thermostat. You can actually trace the hose to the back side of the
thermostat housing. With those setups the thermostat does have to open
before it will discharge a stream while idling. It should, though,
discharge
some when you rev them while cold. The system is also pressure based which
should override the thermostat system.



"Andy C" wrote in message
...
mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local
dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy

mercury force
 

Andy C wrote:
That seems a long
time. While the outboard is running, its waterpump impeller is spinning
and pulling water up into the powerhead for cooling. There's no
auto-type radiator in an outboard, so where would all that water being
pumped up into the powerhead be stored?

hi harry, there are other 'pee holes' in the gear unit before the water gets
to the powerhead, so the water can keep flowing regardless of whether it's
flowing through the powerhead or not...
andy


Thanks. I suppose I should spend more time underwater, watching the
lower unit! (Hmmm. No, that wouldn't work, either)

--
Email sent to is never read.

mercury force
 

For a pressure controlled system Merc uses a spring loaded poppet valve.
When pump pressure comes up the poppet is pushed open and allows for greater
water flow. The thermo itself just doesn't flow enough water to keep things
cool at WOT.

If I remember right, the poppet is located in the same housing as the thermo
on your engine (it has been a while since I've seen a 75 Merc and at my age
memory is not always my friend). The other place Merc puts the poppet is at
the bottom of the block, stbd side, just forward of the head.

I agree with you, the setup has always struck me as unusual, but then again
it does work well.

Ken

"Andy C" wrote in message
...
thanks ken,
yes, the hose is on the back of the thermostat housing as described, so i
guess this is normal... i thought there would be some sort of bypass to
keep
the telltale going all the time the engine is running
it just seems like a strange set up... presumably in very cold water the
thermostat could open and close constantly and you would not be able to
tell
if the water pump was working or not...

It should, though, discharge
some when you rev them while cold. The system is also pressure based
which
should override the thermostat system.

i don't quite follow that, are you saying the water pressure will force
the
thermostat open above idle ?

thanks !
andy

"Ken" wrote in message
...
A lots of Mercs and Mercury-Force place the tattle-tale after the
thermostat. You can actually trace the hose to the back side of the
thermostat housing. With those setups the thermostat does have to open
before it will discharge a stream while idling. It should, though,
discharge
some when you rev them while cold. The system is also pressure based
which
should override the thermostat system.



"Andy C" wrote in message
...
mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local
dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy

mercury force
 

thanks ken that makes good sense, i did look for some sort of pressure
relief valve but didn't see anything - i'll have another proper look ! it's
a Force powerhead though, not a 'proper' Merc :-) i wonder if it's possible
the engine is too basic to have one ?
thanks again,
andy

"Ken" wrote in message
...
For a pressure controlled system Merc uses a spring loaded poppet valve.
When pump pressure comes up the poppet is pushed open and allows for
greater
water flow. The thermo itself just doesn't flow enough water to keep
things
cool at WOT.

If I remember right, the poppet is located in the same housing as the
thermo
on your engine (it has been a while since I've seen a 75 Merc and at my
age
memory is not always my friend). The other place Merc puts the poppet is
at
the bottom of the block, stbd side, just forward of the head.

I agree with you, the setup has always struck me as unusual, but then
again
it does work well.

Ken

"Andy C" wrote in message
...
thanks ken,
yes, the hose is on the back of the thermostat housing as described, so
i
guess this is normal... i thought there would be some sort of bypass to
keep
the telltale going all the time the engine is running
it just seems like a strange set up... presumably in very cold water the
thermostat could open and close constantly and you would not be able to
tell
if the water pump was working or not...

It should, though, discharge
some when you rev them while cold. The system is also pressure based
which
should override the thermostat system.

i don't quite follow that, are you saying the water pressure will force
the
thermostat open above idle ?

thanks !
andy

"Ken" wrote in message
...
A lots of Mercs and Mercury-Force place the tattle-tale after the
thermostat. You can actually trace the hose to the back side of the
thermostat housing. With those setups the thermostat does have to open
before it will discharge a stream while idling. It should, though,
discharge
some when you rev them while cold. The system is also pressure based
which
should override the thermostat system.



"Andy C" wrote in message
...
mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local
dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy

mercury force
 

Yes, I just did a rebuild on a 1993 - 3 cylinder 90 , and it too used the
poppet valve approach. A lot of the older stuff I work on has no thermostat
or poppet. The cooling flow is the cooling flow, and at high rpm's the pump
just can't push more water than the block will pass.

On my late 80's 115, the water comes in, fills the exhaust plates and then
spills over into the top of the block area. The block "top fills" from the
bottom up. When the water gets to the top of #1, the peeing starts.
Amazingly, this takes only about 10 seconds or less.

As a quick side note, I advise anyone running an earlier Merc inline 6 to
plug off the hole where the pee hose goes (with a plastic plug) and to move
the elbow fitting to the very top of the block over #1.

Mercury *finally* did this very late in production. It cures two problems:
It becomes impossible to get an air pocket up in the top, and you won't get
a "pee reading" unless the block is truely full to the very top.

-W

"Ken" wrote in message
...
For a pressure controlled system Merc uses a spring loaded poppet valve.
When pump pressure comes up the poppet is pushed open and allows for
greater
water flow. The thermo itself just doesn't flow enough water to keep
things
cool at WOT.

mercury force
 

Unless I've overlooked someone else mentioning it in the thread here, I'll
say a water pressure gauge is a good idea. There is a spec on the pressure
you should have at high rpm's and as the impeller wears this will drop off.
I've noticed on my '88 200hp merc that, after cranking, it takes a minute or
two to see a stream out the back, but the wp shows maybe 10psi, at idle,
within 10 seconds after cranking--long before I see water out the tel-tale.
I put the fitting for the wp at the top of the block where there was a plug.
If you do look at the gauge it can be valuable in saving your engine. I've
gotten in the habit of looking at that gauge always after cranking. If I
don't see pressure after 10-20 seconds, I'll shut it down and find out why.
LD

"Ken" wrote in message
...
For a pressure controlled system Merc uses a spring loaded poppet valve.
When pump pressure comes up the poppet is pushed open and allows for
greater
water flow. The thermo itself just doesn't flow enough water to keep
things
cool at WOT.

If I remember right, the poppet is located in the same housing as the
thermo
on your engine (it has been a while since I've seen a 75 Merc and at my
age
memory is not always my friend). The other place Merc puts the poppet is
at
the bottom of the block, stbd side, just forward of the head.

I agree with you, the setup has always struck me as unusual, but then
again
it does work well.

Ken

"Andy C" wrote in message
...
thanks ken,
yes, the hose is on the back of the thermostat housing as described, so
i
guess this is normal... i thought there would be some sort of bypass to
keep
the telltale going all the time the engine is running
it just seems like a strange set up... presumably in very cold water the
thermostat could open and close constantly and you would not be able to
tell
if the water pump was working or not...

It should, though, discharge
some when you rev them while cold. The system is also pressure based
which
should override the thermostat system.

i don't quite follow that, are you saying the water pressure will force
the
thermostat open above idle ?

thanks !
andy

"Ken" wrote in message
...
A lots of Mercs and Mercury-Force place the tattle-tale after the
thermostat. You can actually trace the hose to the back side of the
thermostat housing. With those setups the thermostat does have to open
before it will discharge a stream while idling. It should, though,
discharge
some when you rev them while cold. The system is also pressure based
which
should override the thermostat system.



"Andy C" wrote in message
...
mercury force '97 75hp
hi there,
does anyone know if it is normal for there to be no flow from the
tell-tale
until the thermostat opens ?
there doesn't seem to be any cooling problems but it seems weird for
nothing
to come out the tell-tale for the first 2 or 3 minutes... the local
dealer
thought this was normal but didn't seem sure...
many thanks for any comments !
andy