I was wondering if anyone could tell me what the operating water pressure range should be for a HP 525?

Not sure but merc is having me install pressure release valves on my twins about $100 each plus hoses and water dumps.my mechanic just finished them thurs.I was running about 30 lbs at 4000 rpms and buried the needle at WOT.Will let you after sat. what it did on the water.

I believe the operation manual calls for a maximum pressure of 25 psi. I am running a single 525 EFI and was seeing ~30 psi. @ 3500 RPM and probably 40 psi. at 5200 RPM. I installed the relief valve and now I am seeing ~20-25 psi.

Ran mine friday after valves installed and got 25-28 at 4000 rpms and 28-30 at 5000 rpms.my merc rep is coming to recal my ecu's for the raw fuel problem i'll ask him what to do about still having that much water pressure after they where installed.

Water psi is 25-35 psi WOT. The 525efi is not as critical,if it goes over the 35psi, because of the closed cooling system. However, to much and you will find that your typical hose clamp will not hold very well. Over 35 psi on a raw water cooling system can cause gasket eruptions. More than likely you would see water dripping down the side of the block coming from the head gasket area. Also you do not want less than 25 psi at WOT for proper cooling.

Could this explain me always having a half inch of mystery water in the bilge? I thought it was the water pump but it still exists.... If the head gasket is leaking and I put a relief valve... would I have to do the head gasket?

Are you referring to the 525 efi regarding your head leaking? If you are there would be anti-freeze in the bilge not water. The water psi does not effect the internal engine, as far as too much, on the 525 efi or any closed cooled motor for that matter. However, if you are referring to just a standard raw water cooled motor a relief will work. (Size and placement does matter) Yes you do need to change head gasket because that water you see leaking could be entering the combustion chamber also.

Nope.. no antifreeze.... just a little water in the bottom of the bilge.... any thoughts? condensation?

Maybe It Is Your Beer Cooler Or A Hose Leaking.