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.