Hi all,

Trying to diagnose my 1993 OMC Cobra 4.3L water flow troubles. The
motor starts and runs well, but no water flows thru the engine. I
removed the thermostat to rule out whether this could be the trouble.
Even with the thermostat out, there still is no water flow. Short of
taking out the water pump next, is there anything else I can try before
I target the water pump?


thx in advance,

adym

Boater,

I'm assuming this is a sterndrive. Also assume the drive water pump
provides the pressurized cooling water flow and that the engine is raw water
cooled. The engine mounted pump is simply for circulation of the cooling
water.

There are a couple of possibilities: First and most obvious is that the
drive pump requires a new impeller, particularly if the engine was run while
the drive was out of the water. Second is that a hose may have kinked.
Third is that the drive has sucked something into the water passages and
flow is now restricted.

Try this. Reinstall the thermostat. Put the muffs on the drive and supply
water to the unit. Is water now flowing out of the prop hub? Now remove
the manifold drain plugs and allow the water to flush until it runs clear.
Repeat with the block drain plugs. If the elbows have drains repeat there.
Remove the engine mounted water circ pump plug and repeat the process. Also
remove the water hoses on the engine and flush them. If there is water
flowing out the prop hub start the engine after replacing all plugs and
connecting all hoses. Don't run the engine above idle speed. If after a
few minutes the water coming out the hub becomes hot but not steaming the
temp gage should be above the cold mark but not above normal. If that is
the case try an in the water test. If the engine begins to overheat it's
time for an impeller kit in the drive.

Butch
"boater101" wrote in message
oups.com...
Hi all,

Trying to diagnose my 1993 OMC Cobra 4.3L water flow troubles. The
motor starts and runs well, but no water flows thru the engine. I
removed the thermostat to rule out whether this could be the trouble.
Even with the thermostat out, there still is no water flow. Short of
taking out the water pump next, is there anything else I can try before
I target the water pump?


thx in advance,

adym

Butch Davis wrote:

Boater,

I'm assuming this is a sterndrive. Also assume the drive water pump
provides the pressurized cooling water flow and that the engine is raw water
cooled. The engine mounted pump is simply for circulation of the cooling
water.

There are a couple of possibilities: First and most obvious is that the
drive pump requires a new impeller, particularly if the engine was run while
the drive was out of the water. Second is that a hose may have kinked.
Third is that the drive has sucked something into the water passages and
flow is now restricted.

Try this. Reinstall the thermostat. Put the muffs on the drive and supply
water to the unit. Is water now flowing out of the prop hub? Now remove
the manifold drain plugs and allow the water to flush until it runs clear.
Repeat with the block drain plugs. If the elbows have drains repeat there.
Remove the engine mounted water circ pump plug and repeat the process. Also
remove the water hoses on the engine and flush them. If there is water
flowing out the prop hub start the engine after replacing all plugs and
connecting all hoses. Don't run the engine above idle speed. If after a
few minutes the water coming out the hub becomes hot but not steaming the
temp gage should be above the cold mark but not above normal. If that is
the case try an in the water test. If the engine begins to overheat it's
time for an impeller kit in the drive.

Butch
"boater101" wrote in message
oups.com...
Hi all,

Trying to diagnose my 1993 OMC Cobra 4.3L water flow troubles. The
motor starts and runs well, but no water flows thru the engine. I
removed the thermostat to rule out whether this could be the trouble.
Even with the thermostat out, there still is no water flow. Short of
taking out the water pump next, is there anything else I can try before
I target the water pump?


thx in advance,

adym


The question should be did he run the engine up to temp. and wait for a
call for cooling.

When was the impeler last changed in the lower unit? It's a good place to
start.

"boater101" wrote in message
oups.com...
Hi all,

Trying to diagnose my 1993 OMC Cobra 4.3L water flow troubles. The
motor starts and runs well, but no water flows thru the engine. I
removed the thermostat to rule out whether this could be the trouble.
Even with the thermostat out, there still is no water flow. Short of
taking out the water pump next, is there anything else I can try before
I target the water pump?


thx in advance,

adym

OK. Lots of updates as I have been busy trouble-shooting the various
avenues...

First to answer some questions :
snip
Butch Davis asked : I'm assuming this is a sterndrive.
Dry asked : The question should be did he run the engine up to temp.
and wait for a call for cooling.
Woodchuck asked : When was the impeler last changed in the lower unit?
It's a good place to start.
/snip

- Yup, it's a sterndrive.
- Yes, the motor reached operating temp while the thermostat was in
place...However, now that I've pulled the thermostat out, would it even
matter whether the motor reaches temp or not. At this point, I'm just
trying to get water flowing.
- The Impeller has been changed.

Now for some updates :
- I tested to make sure the impeller was turning. Basically pulled the
impeller housing off and started the engine...impeller was turning
fine.
- I tested for any blockage between the impeller unit on the outdrive
into the engine compartment. From within the boat's engine
compartment, I pulled the hose coming from the sterndrive/impeller.
This is the hose located near the back of the engine, where the engine
meets the outdrive, not up near the thermostat. I then pulled the
impeller unit off on the outside/outdrive. Using a garden hose from
the engine compartment I was able to run water backwards out thru to
the impeller...basically, no blockage.
- Put the impeller unit back onto the outdrive BUT left the hose off on
the inside (engine compartment). I then started the motor to see if
any flow would at lease come in...still nothing.
- I've also tested both hoses within the engine compartment coming from
the impeller nozzle, both have no blockage.
- I did "not" test the "filter" (at least I think it's a filter). It
looks like a large version of an inline fuel filter. I didn't bother
testing this as I wasn't getting any flow into the engine compartment
anyway. This filter (or whatever it is) is placed within the engine
compartment between the impeller nozzle and the thermostat, thus the
need for two different hoses...one from the impeller nozzle to this
filter, then a second hose from the filter to the thermostat.

Anyway, I'm running out of options...Does anyone have any other ideas?


thx in advance,

adym

The "filter" is on my mercruiser the oil cooler. Raw water from the impeller
flows through this on it's way to the engine water pump. Look for two
smaller lines (in/out) which (on my GM engine) are oil.


- I did "not" test the "filter" (at least I think it's a filter). It
looks like a large version of an inline fuel filter.

Check. That's what it is, an oil cooler. I saw the two smaller lines
coming off earlier but didn't trace them to the end.

I've also discovered another troubling issue. Seems the two block
plugs along the passenger side of the engine block are coming out. In
fact, when I hook up a garden hose directly into the thermostat to
supply water to the engine (thus bypassing the impeller system
altogether). Water is gurgling out/around one of the engine block
plugs. Figures, it's the block plug directly beside the motor mount,
thus I can't get a clear look at what the "true" problem might be.

Anyone know how these block plugs get put back in? Obviously, I'll be
taking this to a marina...I simply don't have the tools and equipment
to lift/hold an entire engine and/or any special tools needed to put an
engine plug back in.

But, it would be good to hear from others that have seen and/or had
this type of thing done. Maybe get an idea of the cost involved and/or
the difficulty involved.

thx in advance,

adym

"boater101" wrote in message
oups.com...

Seems the two block
plugs along the passenger side of the engine block are coming out. In
fact, when I hook up a garden hose directly into the thermostat to
supply water to the engine (thus bypassing the impeller system
altogether). Water is gurgling out/around one of the engine block
plugs. Figures, it's the block plug directly beside the motor mount,
thus I can't get a clear look at what the "true" problem might be.

Anyone know how these block plugs get put back in?


It sounds like you have freeze damage, possilby a cracked block too, or the
motor was an automotive block with rusted thru core plugs that were steel,
not brass. It's time for the professionals to check it out for you.

Bill Grannis
service manager

Oops ... my mistake, it's the power steering cooler ... d'oh.

"Bowgus" wrote in message
...
The "filter" is on my mercruiser the oil cooler. Raw water from the
impeller
flows through this on it's way to the engine water pump. Look for two
smaller lines (in/out) which (on my GM engine) are oil.


- I did "not" test the "filter" (at least I think it's a filter). It
looks like a large version of an inline fuel filter.

Don't rule out the possibility that when the impeller was
changed, the rubber seal ring wasn't properly seated. The impeller
needs to be installed carefully.
I assume the entry screen at the base of the drive has been
checked for blockage.




On 10 Jul 2005 08:39:45 -0700, "boater101"
wrote:

OK. Lots of updates as I have been busy trouble-shooting the various
avenues...

First to answer some questions :
snip
Butch Davis asked : I'm assuming this is a sterndrive.
Dry asked : The question should be did he run the engine up to temp.
and wait for a call for cooling.
Woodchuck asked : When was the impeler last changed in the lower unit?
It's a good place to start.
/snip

- Yup, it's a sterndrive.
- Yes, the motor reached operating temp while the thermostat was in
place...However, now that I've pulled the thermostat out, would it even
matter whether the motor reaches temp or not. At this point, I'm just
trying to get water flowing.
- The Impeller has been changed.

Now for some updates :
- I tested to make sure the impeller was turning. Basically pulled the
impeller housing off and started the engine...impeller was turning
fine.
- I tested for any blockage between the impeller unit on the outdrive
into the engine compartment. From within the boat's engine
compartment, I pulled the hose coming from the sterndrive/impeller.
This is the hose located near the back of the engine, where the engine
meets the outdrive, not up near the thermostat. I then pulled the
impeller unit off on the outside/outdrive. Using a garden hose from
the engine compartment I was able to run water backwards out thru to
the impeller...basically, no blockage.
- Put the impeller unit back onto the outdrive BUT left the hose off on
the inside (engine compartment). I then started the motor to see if
any flow would at lease come in...still nothing.
- I've also tested both hoses within the engine compartment coming from
the impeller nozzle, both have no blockage.
- I did "not" test the "filter" (at least I think it's a filter). It
looks like a large version of an inline fuel filter. I didn't bother
testing this as I wasn't getting any flow into the engine compartment
anyway. This filter (or whatever it is) is placed within the engine
compartment between the impeller nozzle and the thermostat, thus the
need for two different hoses...one from the impeller nozzle to this
filter, then a second hose from the filter to the thermostat.

Anyway, I'm running out of options...Does anyone have any other ideas?


thx in advance,

adym