I checked my water pressure on merc scan tool this weekend and it topped out at 43.4 psi at around 3500-3600 rpms. It was pretty high at all rpm's up to that point and climbed gradually as rpm's increased. What should top psi be on the 496 ho's? I think 43 psi is way too high and that's what's causing my winterize dump valve to leak water.

Question: What would be the most likely reason that my pressure is so high and where to start looking first to resolve the problem?

Thanks...

Harper,
Itll be two weeks before Im back down at loto, but if ya want, Ill try and borrow a scan tool and check the pressure on my stock 496 ho's with stock length bravos. I do have water pickups under the hull so not sure how yours is set up.

What was the pressure reading key on engine off value?

The best check is to push with your thumb on one of the water hoses. IF you REALLY have that much pressure it will be hard as a rock. I doubt most hose clamps would be able to keep the hose from blowing off. Idle PSI should be 1.5 to 3 lbs. with it gradually going up, (as the RPMs increase) to about 26 to 28 lbs.

If it turns out you really have more than the rated pressure, (and the hose is very hard), look for a restriction in the thermostat housing or the exhaust system.

In some boat's x-dimension configuration there is a problem with too much water pressure which can also cause a soft alarm. Too long can also contribute to head gasket failure (blown). The resulting fix in many is to install a pressure relief valve in the line expelling excess pressure overboard thru a discharge portal...Not saying that's your issue, but it has happened.