So , changed out the port side impellor ,housing, seals and bearings. Have done this job many times. Fire it up , have 40 psi at idle on the garden hose. Launch, test run and the pressure gauge is pegged at 3200 rpm's! What could I have done wrong that would INCREASE water pressure? Old impellor and housing were intact when removed , no missing pieces to restrict anything. Have gone thru the past forums on the subject , stumped. I have ordered a new pressure sender even tho I'm doubtful that is the problem. Engine operating at 150 degrees underway as always. Anyone have any ideas?
Thanks, Bill

If it wasn't doing that before you changed the pump, it's unlikely it is the sender but changing it can't hurt. Are you sure you put the hoses back on the right ports? oriented the impeller vanes properly? are you sure nothing fell into one of the hoses while they were disconnected? just grasping at straws here...

Well Hy, I thought I was sure of all those things but I guess I need to hit the marina and do some double checking. I agree it is unlikely its the sender , was the only thing I could think to do about the situation while at work yesterday, it was driving me crazy so spending some $ seemed appropriate! I have done this so many times I am struggling with thinking I f'ed up somewhere but anything is possible. And yes , pressures were normal before the change , was just doing preventative maintenance. Thanks for your thoughts!

First start of the year,? Maybe rust or scale plugging a passage somewhere

Is the pressure reading high on the dash gauge ?

If so, it's a mechanical gauge with rubber hose connecting it to the cooling system. If was not drained/blown out it may have froze or could have sediment in line. Remove line from gauge and engine connection, then blow out.
Also can swap lines from port to starboard gauges and see if high pressure readings follow to indicate the gauge as the issue.

Kelly , really , thought for sure it was an electronic gauge or I would have tried that already. And yes , reading high on the dash gauge but engine temps are normal. Going to check this out and also try the gauge swap test. It was my first winter with this boat and I never thought to blow out the lines. Where does it connect to the cooling system? At the sender I just ordered?
Thanks !

Don't know for sure, but would guess it's tee'd into the fitting on oil cooler that holds the electronic sensor.

Follow the 1/4" or 3/8" black rubber hose (looks like rubber fuel line) to where it hooks in on seawater side of cooling system.

The water pressure sensor is on the oil cooler on the back left side. It is usually tee'd in with a mechanical gauge hose coming out of the tee and up to the gauge. Kelly has a good point. I wasnt considering this was your first start after winter. If that hose is clogged, that could cause your problem. Disconnect that hose from both ends and blow compressed air through it. If you picked up any sand last season, it could be crusted in there and solidified from the winter.

Thanks guy's , really appreciate the informed advice. I will be going thru your checklists tomorrow after work. Kills me to wait until Friday but work demands will keep me busy late tonight. Still suffering thru the learning curve coming from carbed 502's. I will report back with the results. Hoping the result is me hitting my favorite dockside restaurant Saturday by boat!

So what did you find here flatlanerbill. Ive got a similar problem with my 04 525, not that high of pressure though.