Pressure valve stuck? Water flow issues, 74 Johnson 85hp

[kippstakes]

Took the boat out today for first time after impeller installation. I installed a 'tell tube' in the upper side of the right head, and water seemed to flow fine to the heads at idle with cuffs. Also, the vernatherm element seems to be opening its valve since water sprays from the two holes on the rear of the exhaust housing (I hear that's what that indicates).

Here's the thing, I took her out today for the first time and everything seemed to be working fine. However, when I put the juice to it the water stopped flowing from the tell tube and I was just getting steam. Actually, it was probably just boiling off from the increased engine temp- not enough water flowing. The engine overheated.. lots of steam, yikes (I actually confused the steam from the tell tube for water spray- oops).
As I understand it, water flows continuously to the heads from the pump til the thermostat kicks in (at low revs) or the pressure valve is forced open and water flows OUT, to be replaced by fresh/cold water.

Would a stuck pressure valve be a likely cause for weak water flow? Considering that water flow from the tell line, which indicates flow to the head, didn't indicate increased flow at higher revs, the problem seems to precede the pressure valve. So maybe not??
Not sure what to think here, and the thermo housing is corroded on like concrete, and I'd like to avoid getting invasive with it.

This is my thermo setup..

 

[racerone]

Have you inspected / replaced the water " deflecters "-------------Rubber parts that guide water for proper cooling,-----You must remove heads to find them !

 

[F_R]

When the thermostat is closed, water pressure opens the pressure check valve and flows back to the water pump for recirculation. When the thermostat is open, hot water is discharged and the relief valve is closed, preventing water return to the pump, and cool lake water enters the system. That is an ongoing balancing act as the thermostat is constantly sampling the water temp and opening or closing as necessary to maintain proper temp. It is not a simple matter of either/or.

The check valve does not "stick" but could be held open by debris. Or it could be melted from extreme overheating.

 

[kippstakes]

Hmm. Okay sounds like I didn't have it quite right (not surprised). Guess I just need to tear that thermo cover off and service the system. This is gunna be rough.
Thank you for the explanation.