2005 496HO with closed cooling. When reading live data with the boat running at WOT my block pressure occasionally goes over 40 psi and trips the two beeps on Smartcraft. This only happens at WOT and around 4900-5000 rpms. The Rinda fault code says Sea Pump/Block pressure high. All the temperature readings are normal. The boat has through hull water pickups. Water pressure sensor has been replaced with same results and seems to be operating correctly starting at 0 psi and increasing with boat speed. The other motor never gets above 35 psi and has no alarm issues.

Also what are the manifold pressure readings you get when viewing live data? Mine starts at 0 and increases to 13.5 psi at WOT. Any help is appreciated!

IMO you have blockage in the cooling system water side. I would start at the oil cooler and keep on moving thru other / ALL water side cooling AREAS to clean out what ever has collected causing a restriction.

Agree 100%. Every time I had high water pressure it was a blockage in the oil cooler. I'm installing a sea strainer as I type this.

Bad ground contact causes the pressure sensor failure and or incorrect readings so does RFI - especially if plug wires are to close or any other source of RFI. Another reason why Merc moved the WPS to the back side pwr steering cooler. . And one needs to buy the 50 psi inwhich is the newest part number from years ago. Hopefully he does have the correct WPS installed.

The poster said he changed the WPS to brand new. MY money is on what I posted above in post number 2.

Thanks BUP and others for your quick response on a Sunday morning so I had time to work on the boat. Inlet side of the oil cooler had quite a bit of fine brown sea grass in it. I cleaned all that out and back flushed the cooler. Took the boat for a ride and high block pressure alarm was still there at 5000 rpm. I then took the end cap off the inlet side of the heat exchanger. Found more grass in there (not as much). The other thing I found was the gasket was all sucked in with the section by the water inlet actually torn at the rim and flapping in that section. I am thinking this is my problem. The holes in the exchanger seem clean. Boat is an 05 but with only 150 hours on it. So I cleaned it out and have ordered 2 gaskets and o-rings. When I get the new parts I will remove the other end cap, back flush the exchanger and put it back together and test. I will post the outcome later this week. Once I cure this alarm I am definitely going to change the gaskets on the other motor and back flush the oil cooler. They look like they have never been changed. I searched the gasket issue and then found BUP has reported this issue before. Thanks again!

Follow up report.......Problem was the gaskets on both the ends of the heat exchanger. Both were deteriorated and sucking into the water tubes causing a restriction. Easy to change and all pressures back to normal at 5000 rpms after cleaning the pieces out of the exchanger. Ill be changing the ones on the other motor as soon as I get them. Thanks all for your guidance. BUP was right on!

How did you get the pieces out of the exchanger? Did you need to remover the exchanger? I have an 2004 496 and it sounds like this is worth doing before problems show up.

Very easy nighthawk. Take the one bolt off each end and use a small screwdriver to pry the cap and gasket off. In mine the pieces (and a little lake grass) were in the water inlet end (port side of motor). I then ran a small piece of wire through the tubes in the exchanger to be sure and backflushed with a garden hose from the other end. Cleaned the gasket surfaces with a little sandpaper and put a new gasket and o-ring on. Did it on the boat. You can do it in 15-20 minutes