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

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.

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.

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.

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

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)

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Email sent to is never read.

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

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

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

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