Hi. I'll try and be brief. I have a 7.4L merc, Bravo one raw water
cooled, moored in shallow salt water (gross I know). I have a new
impeller in my water pump which I change every season. I also have a
new thermostat housing I installed just before going in the water.
The old one had some corrosion I didn't like. It's 16 years old. At
idle my temp hits 160 and stays. I've run her 4 times so far.
During my first run after dropping her in the water at about 3000 rpm
my temp started creeping up to 170. This has never happened so I
backed down and temp came down to "normal". My second and third time
out the temp stayed at 160 through all speeds. Yesterday I ran her
and the temp was creeping up over 170 again. Starboard side manifold
was hotter than port. The fact it's been inconsistent has me
thinking or hoping it could just be my thermostat not opening properly
but why would temp be normal at idle. Any thoughts on what would
cause rising temp under load one day and not another? I'm not going
to be able to get back out the boat until this weekend but this is
eating me up and wonder if anyone had any thoughts. Thank you.

On May 14, 10:57*am, wrote:
Hi. I'll try and be brief. *I have a 7.4L merc, Bravo one raw water
cooled, moored in shallow salt water (gross I know). *I have a new
impeller in my water pump which I change every season. *I also have a
new thermostat housing I installed just before going in the water.
The old one had some corrosion I didn't like. It's 16 years old. *At
idle my temp hits 160 and stays. I've run her 4 times so far.
During my first run after dropping her in the water at about 3000 rpm
my temp started creeping up to 170. *This has never happened so I
backed down and temp came down to "normal". *My second and third time
out the temp stayed at 160 through all speeds. *Yesterday *I ran her
and the temp was creeping up over 170 again. *Starboard side manifold
was hotter than port. * The fact it's been inconsistent has me
thinking or hoping it could just be my thermostat not opening properly
but why would temp be normal at idle. * Any thoughts on what would
cause rising temp under load one day and not another? *I'm not going
to be able to get back out the boat until this weekend but this is
eating me up and wonder if anyone had any thoughts. *Thank you.

Always suspect the last work done.

Fwiw with raw water cooling I think you should be using the 140 deg
thermostat. Particularly in salt water. Is that what you have? Do
you know what is the stock one?

I'd also check for corrosion blockage in the manifolds and risers.
How old are they? And how long have they been running in salt water?

It is fairly easy to keep an idling motor cool. It's a whole nother
deal to keep one under load cool so that could explain your problems
under load. As to the differences on different days. Water temps
maybe? Or blockage shifting around a bit in the manifolds or risers?

ALso make sure that you have reassembled the thermostat housing
properly and that the plastic poppers are working freely.

It sounds like the cooling system arteries are starting to clog up. At 16
years you should be on your 3rd set of risers and 2nd set of manifolds. The
wear plates and gaskets should be replaced whenever you replace the water
pump impeller. Hoses and belts should be carefully inspected. Make sure you
are not sucking air on the pump inlet side due to loose hose clamps etc.Did
you use a 143 deg. thermostat?

wrote in message
...
Hi. I'll try and be brief. I have a 7.4L merc, Bravo one raw water
cooled, moored in shallow salt water (gross I know). I have a new
impeller in my water pump which I change every season. I also have a
new thermostat housing I installed just before going in the water.
The old one had some corrosion I didn't like. It's 16 years old. At
idle my temp hits 160 and stays. I've run her 4 times so far.
During my first run after dropping her in the water at about 3000 rpm
my temp started creeping up to 170. This has never happened so I
backed down and temp came down to "normal". My second and third time
out the temp stayed at 160 through all speeds. Yesterday I ran her
and the temp was creeping up over 170 again. Starboard side manifold
was hotter than port. The fact it's been inconsistent has me
thinking or hoping it could just be my thermostat not opening properly
but why would temp be normal at idle. Any thoughts on what would
cause rising temp under load one day and not another? I'm not going
to be able to get back out the boat until this weekend but this is
eating me up and wonder if anyone had any thoughts. Thank you.

wrote in message
...
On May 14, 10:57 am, wrote:
Hi. I'll try and be brief. I have a 7.4L merc, Bravo one raw water
cooled, moored in shallow salt water (gross I know). I have a new
impeller in my water pump which I change every season. I also have a
new thermostat housing I installed just before going in the water.
The old one had some corrosion I didn't like. It's 16 years old. At
idle my temp hits 160 and stays. I've run her 4 times so far.
During my first run after dropping her in the water at about 3000 rpm
my temp started creeping up to 170. This has never happened so I
backed down and temp came down to "normal". My second and third time
out the temp stayed at 160 through all speeds. Yesterday I ran her
and the temp was creeping up over 170 again. Starboard side manifold
was hotter than port. The fact it's been inconsistent has me
thinking or hoping it could just be my thermostat not opening properly
but why would temp be normal at idle. Any thoughts on what would
cause rising temp under load one day and not another? I'm not going
to be able to get back out the boat until this weekend but this is
eating me up and wonder if anyone had any thoughts. Thank you.

Always suspect the last work done.

Fwiw with raw water cooling I think you should be using the 140 deg
thermostat. Particularly in salt water. Is that what you have? Do
you know what is the stock one?

I'd also check for corrosion blockage in the manifolds and risers.
How old are they? And how long have they been running in salt water?

It is fairly easy to keep an idling motor cool. It's a whole nother
deal to keep one under load cool so that could explain your problems
under load. As to the differences on different days. Water temps
maybe? Or blockage shifting around a bit in the manifolds or risers?

ALso make sure that you have reassembled the thermostat housing
properly and that the plastic poppers are working freely.

I don't remember if the 454 uses the plastic balancing valves, but if it
does, worn balls can be flipped over and seal like new again.

ALso make sure that you have reassembled the thermostat housing
properly and that the plastic poppers are working freely.- Hide quoted text -

- Show quoted text -

I agree with the last work done being the probable culprit. As I think
about it, the plastic poppers may be a little looser than they should
be (my fault, but easy to fix), if so, do you think the pressure could
force only one side open sending water to the port and not starboard
in this case? I'm going to pull the riser and check the manifold for
anything visible, they need to be replaced as a preventative measure
anyway. My risers are stainless. The boat was a freshwater boat most
of its life, this is year 3 in the salt. I have to admit a few of the
manifold bolts were pretty frozen and rusted round so I put the
project off hoping to get another season as they may need to be cut
off by a pro. Bad idea, I know. I often flush with fresh water and
at least run the engine 3-4 times a week to keep water flowing and
crap from building up the best I can. I'm going to check my flapper
also, I replaced the port one last season because it was making noise,
I should have done starboard at the same time but I was in a if aint
broke don't fix it mood. Thanks

On May 14, 11:58*am, wrote:
ALso make sure that you have reassembled the thermostat housing
properly and that the plastic poppers are working freely.- Hide quoted text -

- Show quoted text -

I agree with the last work done being the probable culprit. As I think
about it, the plastic poppers may be a little looser than they should
be (my fault, but easy to fix), if so, do you think the pressure could
force only one side open sending water to the port and not starboard
in this case? I'm going to pull the riser and check the manifold for
anything visible, they need to be replaced as a preventative measure
anyway. My risers are stainless. The boat was a freshwater boat most
of its life, this is year 3 in the salt. I have to admit a few of the
manifold bolts were pretty frozen and rusted round so I put the
project off hoping to get another season as they may need to be cut
off by a pro. *Bad idea, I know. *I often flush with fresh water and
at least run the engine 3-4 times a week to keep water flowing and
crap from building up the best I can. I'm going to check my flapper
also, I replaced the port one last season because it was making noise,
I should have done starboard at the same time but I was in a if aint
broke don't fix it mood. Thanks

While you're in the thermostat housing check the thermostat. You want
the lower temp one if you're in salt water now. Keeping the water
temp lower will reduce the corrosive effects of the salt water some.
If your boat was originally in fresh water that would explain why it
had 160.

Pulling the risers will probably give you some idea of the condition
of the manifolds. I'd go that route and then decide from there. It
may be that you can clean out any blockage and get back on the water
for another season.

The bolts on the manifolds often get stuck. You can cut the bolt
heads off the offending bolts with a dremel and slide the manifold off
in many installations. Then it's easy to soak the bolt threads where
they go into the engine heads with wd40 or your favorite penetrating
oil for a few days. Then they usualy will come out using vise grips
on the bolt shaft.

"Jim" wrote in message
...
It sounds like the cooling system arteries are starting to clog up. At 16
years you should be on your 3rd set of risers and 2nd set of manifolds.
The wear plates and gaskets should be replaced whenever you replace the
water pump impeller. Hoses and belts should be carefully inspected. Make
sure you are not sucking air on the pump inlet side due to loose hose
clamps etc.Did you use a 143 deg. thermostat?

To each his own I guess. Can't deny I've reused a few gaskets in my life.
I inspect my impeller for a few years and if it's still good I reassemble.
Most kits come with the works though and I'll put in what ever I get in the
kit if I'm replacing the impeller. I'd forgotten about the belt, that's a
good point. Sometimes they only slip while underway and not as much at
idle.

Just to follow up, I replaced the circulating pump because it was
going anyways and the problem was still there. It wound up being crud
blocked up on the backend of my oil cooler on the intake side so not
enough water was getting in the system. I pulled the hose, cleaned it
out and its been perfect since. Thanks all..