I know the story about the low water presser on my engine now!
There are diffrent sensors for the PCM (this is psi what smartcraft show) and for the analog gauges!
There is an higher pressure shown!
The engine can have min 17 Psi max 41 PSI at WOT to get no damage!
You hope you can sometimes close your problem.
michael

OK. I'm going to rule out the results you get with the external pickup because I think the force of the water entering that pickup is what is driving the pressure up so that is somewhat of a false reading. I think if you add an external pickup, you're going to be masking a problem that you really should solve.

You've already ruled out the drives so that's good and you say that all of the coolers are clear. I'm running out of ideas but the next one I have is to check EVERY single hose in the system, not for obstructions but for cracks especially around the area of the hose clamps. A tiny crack would not likely show up when you're flushing or running the engine, but might just suck air under the suction of the sea pump. Try plugging one end of each hose and then pressurize with 20-30 psi of compressed air (you may need to get a few fittings), submerge in water and look for bubbles.

THanks for your input. The external temporary water pick up was an attempt to locate the problem. Since the pressure goes up, the sensor is ok and works. The only air incoming leak I might have is in hoses under negative pressure/suction. All the hoses under positive pressure while it might reduce the reading WP, they don't leak. No water or even any seepage. I'm down to impeller, housing or a f'up vessel view read out. But the temp does creep up a bit, so I'm ruling out the vessel view read out. It might be as simple as having the hose to the intake side of the housing too tight. GGGRrrr stupid me, but I hope that's all it is. ( I use the T clamps) It's possible that I cracked the housing tube by over tightening. In that case I will feel pretty silly, but will post and go hide somewhere.

I'd be pulling the impeller housing back apart, make sure no issues there.
Hoses oriented correctly I assume.

temp creeping up = no good. good luck and please post what you find... even if it is embarrasing...we've all done it..

I had exact same problem last spring. Working backwards.. It was the last hose I checked. The hose in the bell housing became a little twisted some how. I just removed the plastic insert and straitened the hose replaced new insert and all worked fine all summer. Simple problems like this drive you crazy!

Might want to drain and back flush your block as well. Could be some of the small holes in the head gasket stopped up.

How were you able to determine that the hose was twisted? I've looked at mine (with drive installed), and it doesn't look twisted, but not sure I can tell with drive installed.

Thanks.

Did you replace the hard-walled hose between sea water pump and water neck at the transom? I've heard that they can delaminate inside and suck closed. I replaced mine but unfortunately, it had no effect.

525's are closed cooling. Nothing to do with sea water pressure.
1BIGJIM. I swapped the drive intake lines from Port to Starboard. The issue remains, nothing to do with drives or hoses from the drive.

I missed that on the quick read thru, sorry.