496 HO was running too high temp +-180°
engine in guardian mode because exhaust temp too high
replaced the impeller (while boat was in the water)
impeller was completely toasted
brass ware plate showed some signs of wear but not dramatic
Started engine up (+-2 min at idle) still no water pressure at the exhaust manifolds (boat in the water)
Does pump needs to be bleeded? How to?
With old worn out impeller I still had some pressure at the manifolds ....
less with new impeller
All ideas / suggestions welcome
What is correct sea water pump pressure @ idle?

Pump doesn't need bleeding. If you have a sea strainer it might need to be primed. Pressure at idle is only about 2-4 psi.

That's also my first idea... no bleeding required
I have NO strainer, this can't be the problem
what's next to look at?

Did you clean out the old pieces of the impeller? If not you need to back flush it and get them out. They are most likely plugging you water flow.

If there are wear grooves in the pump, it may not pump. Common problem on the 496. I just switched mine over to the stainless Hardin pump so I wouldn't have to worry about it again.

Yup, and check the inlet hose to the pump to make sure it isn't clogged with seaweed or something.

Yea, thats exactly what happened to me on my 25 outlaw, 496 ho. Replaced impeller and flushed out the entire system, still no flow. Replaced the pump, fixed. I guess if the pump housing has the slightest bit of wear it doesn't work at all or very little. Hope this helps. Good luck.

thnx to all reply
I know replacing complete pump is all way to go but
still don't understand with 1/4 of impeller I had "some" water pressure
with new impeller , none...

Because the sides of the old impeller were worn into the grooves.

Let me guess.... Sierra replacement impeller? Had troubles with them before. Swapped it out for a Merc and no problem.