1985 Evinrude 90 Stops Peeing Intermittently

[BeachCreature]

Hello all,
So, I have an '85 90hp that is fairly new to me. Its been a saltwater motor and until recently boat/motor was kept on a trailer.
I replaced the water pump assy (complete) and all thermostat components with Sierra stuff. The old impeller was still intact as were the t/stats and there were minimal deposits in t/stat housing. The problem I have encountered on 2 occasions is that it will pee fine on initial start up but after several minutes it stops and begins blowing steam. Both times it happened I simply shut it down, waited maybe a minute, restarted the engine and it was fine from that point on. What worries me is that when it has happened I was basically just above idle and could hear the hissing of the steam but, if it should happen at speed, I would never know until it was too late. Of course my overheat alarm must not work and I will have to figure that out as well but that is secondary right now.
The first (and really only thing) that comes to mind is the impeller key but can that cause an intermittent problem?
Any input is greatly appreciated!!
-Martin

 

[racerone]

Are you testing in a bucket or with boat launched ?

 

[BeachCreature]

Hey racerone. Both times in the water. The first time it was idling at the ramp while I parked my truck. The second time was shortly after leaving my dock. In between those 2 times I had taken it out 4-5 times with no problem. I always make sure its peeing when I start it up, its a habit I've had for many years especially now.

 

[BeachCreature]

Nothing?
I took it out three times this weekend with no problems.

 

[racerone]

If you have it sitting with fast idle , then there are many exhaust bubbles in the water.-----These pumps do not move air very well.