wrote in message
ups.com...

Melandre wrote:
It takes a couple of minutes to get passed "normal temperature". Then
another minute or so to climb over 200F. Then stays hot for 1 to 3
minutes (in a few occasions a bit longer than 3 minutes), then it
drops back from well over 200F to 150F in about 3 - 5 seconds.


We can be very certain that the cooling system isn't actually dropping
in temp for over 200F to 150F in 3-5 seconds. If you're getting a
report of a condition that seems virtually impossible, one of the first
things to check is the data itself. You sending unit is almost
certainly a screw-in unit with a wire attached to it. A new one would
be very inexpensive.



In a RAW water system that has no water flow it can overheat fairly fast and
the sending unit will show the increased temp, if the water suddenly starts
flowing the sending unit gets very cool raw water running over it almost
immediately and it cools down FAST. In fresh water /heat exchanger systems
the temp of the coolant in the engine can't cool down as fast.

I'd check for a kink in the hose in the outdrive. There is a service note
on Merc outdrives about this problem.

Quick update for those (and thanks to all for feedback so far!) who are
following this tread. Spent Sunday afternoon at the marina still
trying to diagnose the source of the overheating problem. First I
disconnected the hose coming from the transom/leg and going to the
thermostat housing: I started the boat and saw a really good flow of
water coming out of the hose. To me, this would indicate that the raw
pickup of water on the stern drive is not plugged and the two-month old
impeller appears to be pushing water through the hose as it should.

Then I pretty much disconnected, sequencially, all cooling related
hoses going in to and coming out from the engine block. A flow of
water could be seen although I do not know if this flow was normal or
lower than what it should be. The only place that I did not check is
where the hose re-enters the thermostat housing and presumably find its
way to the manifold/riser and then out. So if I am still thinking
blockage, this may be one more place to look: is it easy to remove the
riser cover? With blockage or clogging being a less likely cause, I
am once again looking for other culprits.

Again, restating that I am not very mechanically inclined, I am
starting to think that my problem may be related to a defective water
pump (not the stern drive (impeller) one but the "engine-circulating"
water pump (the one that is spun by the alternator belt I believe). I
see no physical evidence of a defective or clogged water pump but if
that water pump was not turning properly (sliding or whatever) or if it
was clogged or defective (but not 100% broken), could it explain why
when I get on my way and increase RPM, the problem seems to eventually
fixed itself (cooling process starts, needle drops to 150F and all is
well). Perhaps, there is a point where the water pump turns "enough"
to enable the cooling process to happen? Could this explain why the
overheating appears to happen primarily at idle or low speed?

When the boat runs at idle for the first 5 minutes (until the needle
creeps to 200F+) the boat sounds good. No weird or clinging noise or
whatever. As far as I can tell, oil in the engine block is clean
(although I admit I am not sure I would be able to see the difference
if there was water in it - unless it is very obvious). So I am
thinking/praying that I may not have a major problem yet and that the
problem may still reside within the (raw) cooling system itself.

Any comment, advice, suggestion regarding probability of a clogged
manifold/riser or the possibility of having a defective
engine-circulating water pump (even though no external sign of it not
working properly)? Sorry for the long post! Andre

PS: yes, I recognize (and regret!) my lack of mechanical knowledge and
yes, I am looking for the service of a boat mechanic to help me out.
However, they unfortunately all seem pretty busy at the moment!

On 23 Aug 2005 11:53:20 -0700, "Melandre" wrote:

Quick update for those (and thanks to all for feedback so far!) who are
following this tread. Spent Sunday afternoon at the marina still
trying to diagnose the source of the overheating problem. First I
disconnected the hose coming from the transom/leg and going to the
thermostat housing: I started the boat and saw a really good flow of
water coming out of the hose. To me, this would indicate that the raw
pickup of water on the stern drive is not plugged and the two-month old
impeller appears to be pushing water through the hose as it should.

Then I pretty much disconnected, sequencially, all cooling related
hoses going in to and coming out from the engine block. A flow of
water could be seen although I do not know if this flow was normal or
lower than what it should be. The only place that I did not check is
where the hose re-enters the thermostat housing and presumably find its
way to the manifold/riser and then out. So if I am still thinking
blockage, this may be one more place to look: is it easy to remove the
riser cover? With blockage or clogging being a less likely cause, I
am once again looking for other culprits.

Again, restating that I am not very mechanically inclined, I am
starting to think that my problem may be related to a defective water
pump (not the stern drive (impeller) one but the "engine-circulating"
water pump (the one that is spun by the alternator belt I believe). I
see no physical evidence of a defective or clogged water pump but if
that water pump was not turning properly (sliding or whatever) or if it
was clogged or defective (but not 100% broken), could it explain why
when I get on my way and increase RPM, the problem seems to eventually
fixed itself (cooling process starts, needle drops to 150F and all is
well). Perhaps, there is a point where the water pump turns "enough"
to enable the cooling process to happen? Could this explain why the
overheating appears to happen primarily at idle or low speed?

When the boat runs at idle for the first 5 minutes (until the needle
creeps to 200F+) the boat sounds good. No weird or clinging noise or
whatever. As far as I can tell, oil in the engine block is clean
(although I admit I am not sure I would be able to see the difference
if there was water in it - unless it is very obvious). So I am
thinking/praying that I may not have a major problem yet and that the
problem may still reside within the (raw) cooling system itself.

Any comment, advice, suggestion regarding probability of a clogged
manifold/riser or the possibility of having a defective
engine-circulating water pump (even though no external sign of it not
working properly)? Sorry for the long post! Andre

PS: yes, I recognize (and regret!) my lack of mechanical knowledge and
yes, I am looking for the service of a boat mechanic to help me out.
However, they unfortunately all seem pretty busy at the moment!

Removing a riser is not that big a deal. Just have new gaskets and sealant ready
when you reinstall. I'd consider replacing the bolts and nuts also and put some
anti-seize on them for next time.

Have you checked the tension of your belt? I'd definitely look there, and
perhaps replace the belt, which could be old and slipping.

I'm on my third circulation pump. The first lost a seal, and the second lost a
bearing due to an overtight belt (IMHO). The mechanic who installed the
circulating pump was fired shortly after doing the work, so I doubt how well he
checked the belt tension. Now I know to check it myself.

--
John H.
On the 'PocoLoco' out of Deale, MD

There should be a bypass port in your thermostat housing to cool the exhaust
when the thermostat is closed. This port may be blocked.
JIMinFL

"Melandre" wrote in message
ups.com...
Quick update for those (and thanks to all for feedback so far!) who are
following this tread. Spent Sunday afternoon at the marina still
trying to diagnose the source of the overheating problem. First I
disconnected the hose coming from the transom/leg and going to the
thermostat housing: I started the boat and saw a really good flow of
water coming out of the hose. To me, this would indicate that the raw
pickup of water on the stern drive is not plugged and the two-month old
impeller appears to be pushing water through the hose as it should.

Then I pretty much disconnected, sequencially, all cooling related
hoses going in to and coming out from the engine block. A flow of
water could be seen although I do not know if this flow was normal or
lower than what it should be. The only place that I did not check is
where the hose re-enters the thermostat housing and presumably find its
way to the manifold/riser and then out. So if I am still thinking
blockage, this may be one more place to look: is it easy to remove the
riser cover? With blockage or clogging being a less likely cause, I
am once again looking for other culprits.

Again, restating that I am not very mechanically inclined, I am
starting to think that my problem may be related to a defective water
pump (not the stern drive (impeller) one but the "engine-circulating"
water pump (the one that is spun by the alternator belt I believe). I
see no physical evidence of a defective or clogged water pump but if
that water pump was not turning properly (sliding or whatever) or if it
was clogged or defective (but not 100% broken), could it explain why
when I get on my way and increase RPM, the problem seems to eventually
fixed itself (cooling process starts, needle drops to 150F and all is
well). Perhaps, there is a point where the water pump turns "enough"
to enable the cooling process to happen? Could this explain why the
overheating appears to happen primarily at idle or low speed?

When the boat runs at idle for the first 5 minutes (until the needle
creeps to 200F+) the boat sounds good. No weird or clinging noise or
whatever. As far as I can tell, oil in the engine block is clean
(although I admit I am not sure I would be able to see the difference
if there was water in it - unless it is very obvious). So I am
thinking/praying that I may not have a major problem yet and that the
problem may still reside within the (raw) cooling system itself.

Any comment, advice, suggestion regarding probability of a clogged
manifold/riser or the possibility of having a defective
engine-circulating water pump (even though no external sign of it not
working properly)? Sorry for the long post! Andre

PS: yes, I recognize (and regret!) my lack of mechanical knowledge and
yes, I am looking for the service of a boat mechanic to help me out.
However, they unfortunately all seem pretty busy at the moment!

"Melandre" wrote in message
ups.com...
Quick update for those (and thanks to all for feedback so far!) who are
following this tread. Spent Sunday afternoon at the marina still
trying to diagnose the source of the overheating problem. First I
disconnected the hose coming from the transom/leg and going to the
thermostat housing: I started the boat and saw a really good flow of
water coming out of the hose. To me, this would indicate that the raw
pickup of water on the stern drive is not plugged and the two-month old
impeller appears to be pushing water through the hose as it should.

Then I pretty much disconnected, sequencially, all cooling related
hoses going in to and coming out from the engine block. A flow of
water could be seen although I do not know if this flow was normal or
lower than what it should be. The only place that I did not check is
where the hose re-enters the thermostat housing and presumably find its
way to the manifold/riser and then out. So if I am still thinking
blockage, this may be one more place to look: is it easy to remove the
riser cover? With blockage or clogging being a less likely cause, I
am once again looking for other culprits.

Again, restating that I am not very mechanically inclined, I am
starting to think that my problem may be related to a defective water
pump (not the stern drive (impeller) one but the "engine-circulating"
water pump (the one that is spun by the alternator belt I believe). I
see no physical evidence of a defective or clogged water pump but if
that water pump was not turning properly (sliding or whatever) or if it
was clogged or defective (but not 100% broken), could it explain why
when I get on my way and increase RPM, the problem seems to eventually
fixed itself (cooling process starts, needle drops to 150F and all is
well). Perhaps, there is a point where the water pump turns "enough"
to enable the cooling process to happen? Could this explain why the
overheating appears to happen primarily at idle or low speed?

When the boat runs at idle for the first 5 minutes (until the needle
creeps to 200F+) the boat sounds good. No weird or clinging noise or
whatever. As far as I can tell, oil in the engine block is clean
(although I admit I am not sure I would be able to see the difference
if there was water in it - unless it is very obvious). So I am
thinking/praying that I may not have a major problem yet and that the
problem may still reside within the (raw) cooling system itself.

Any comment, advice, suggestion regarding probability of a clogged
manifold/riser or the possibility of having a defective
engine-circulating water pump (even though no external sign of it not
working properly)? Sorry for the long post! Andre

PS: yes, I recognize (and regret!) my lack of mechanical knowledge and
yes, I am looking for the service of a boat mechanic to help me out.
However, they unfortunately all seem pretty busy at the moment!

I've found a quick and dirty method of finding where the problem is in a raw
water cooling system. Provided that the impeller is good, squeeze the hose
and see if it's tighter/stiffer when the impeller/engine is running. If it
gets stiffer then there is blockage downflow from that point.