High seawater pressure

[Schoony]

Good afternoon, I have a 2007 Sea Ray sundancer with a Mercruser 350 mag mpi. I'm having high water pressure form the pump, about 40 psi at idle, and at 22 mph I get the high pressure alarm. I check the pressure with an analog gauge to verify the sensor was working properly and it is correct. I did just replace the impellor, shaft and seals in the seawater pump, the impellor was intact and no part were missing. The boat is only in fresh water on a lift so there is very little corrosion. any help would be appreciated.
Thanks

 

[Espos4]

Was the pressure high before servicing the pump?

Fresh water since 2007?

Possibly clogged elbows?

 

[techmitch]

Sounds like you have a blockage some where after the pump.

 

[Schoony]

Was the pressure high before servicing the pump?

Fresh water since 2007?

Possibly clogged elbows?

No the pressure was normal or low before servicing pump - no codes or alarms before servicing

Boat has always been in fresh water.

 

[Schoony]

THis is at idle

 

[Bill Curtis]

A restriction downstream of the pump is only thing that causes hi pressure. Check the oil / PS cooler for blockage on inlet side. Was the old impeller 100% intact when it was removed?

 

[Schoony]

A restriction downstream of the pump is only thing that causes hi pressure. Check the oil / PS cooler for blockage on inlet side. Was the old impeller 100% intact when it was removed?

Good afternoon, today I took most of the plumbing off of the seawater pump and water pump and ran a borescope through the system. Also took a hose and ran that through the system. Did not find anything like mud or debris at all coming out. Could a newly rebuilt seawater pump produce more pressure for some reason.

 

[PlayDate]

So .....I'm a little confused. Your first post says it is 40 psi at idle and your pictures show 20 psi at idle. Am I missing something?

 

[Schoony]

Sorry for the confusion, when the motor is at idle sitting at the dock its around 20 psi. when that boat is on plane it will alarm at 40 psi. and will start to alarm with 2 beeps and code 36 high sea water pressure.

 

[PlayDate]

So to answer your question.....a rebuilt sea pump will just restore pressure not increase it. Something is restricting the water flow. Unfortunately the only way to figure it out is to test the raw water pressure on different hoses. Since you already have a gauge ....you are ahead of the game.

What I do is make up a few pieces of PVC and do this to find the restriction:

Idle water pressure should be less than 2 psi. Can you post a picture of your engine? Some 350s came with a poppet valve on the top of the motor that if it gets stuck will not bleed pressure correctly.

 

[Schoony]

No. There is not a poppet at the thermostat housing. I will take a picture of that tomorrow and send it to you. The motor is a 350 mpi mag standard coolent system no heat exchanger. SR# 1A049167

 

[Lazy Daze]

As noted above, the raw water pump will not INCREASE pressure past it's specs. There has to be a blockage downstream of the sensor. It's just going to be some trial and error. IF you haven't had the t-stat housing apart, start there as it wouldn't be a bad idea to inspect that housing really well, anyways. And, might as well replace the t-stat while you're at it.

 

[Lazy Daze]

Oh... how does the flow coming out the transom plate compare to previous?