I've got nearly 280 hours on my 496HOs with no issues to speak of, until this weekend. The boat has always had 30-35 lbs. of water pressure via mechanical gauges. I have DWP drives.

This weekend, after changing impellers (new) and being in the salt of South Florida, I was pegging the gauges at 40-45 lbs. at times.

How/why did it go up so drastically?
What is the correct pressure for a 496HO? (Remember, the 496HO has pop off valves for the air-pressure flush system, and mine were opening with so much water pressure at speed.)
What pressure do the air-pressure valves open?

What can I do to decrease the water pressure? I really don't want to install pop off valves and transom dumps if I don't have to, especially if when I get back to Virginia and fresh/slightly brackish water, the pressure drops back down.

Do I block off some of the UWP holes on the drives via tapping them and inserting set screws? (After testing with water proof tape.)

Did you check for blockages?? Like old impeller bits or sand stuck in the heat exchanger, Or a kinked hose, bad manifold etc... Jamie / Lakeside

Impellers are fine. And while I probably had some sand in there at one time, every place that I opened and checked was fine. I even pressurized the system with a compressor, and saw no sand coming out. I've never lost a piece of impeller, and the hoses are straight and true.

My main question is why in the world did the water pressure shoot from 25-30 or so to pegging the gauge at approximately 45 lbs. with impeller changes and running in South Florida salt water as opposed to Virginia river brackish/Chesapeake Bay Salt/Virginia fresh water. That's really got me puzzled.

Did the salt crystalize somwwhere? Pop the rubber boots off the exhaust hose and look for buildup?

Aren't these closed cooling? Where is the pressure taken from, the closed side or the lake side?

If both motors had the same change, I think I'd wait until back on home ground and see if they return to your normal readings before modifying anything. Or maybe the new impellors are just bringing it back to snuff???

Water pressure on mine is taken from the SW side of the system. The I don't know if its before or after the SWP though; I need to do some digging. There is no thermostat on the SW side of the system.

The engine driven WP spins the Antifreeze though the motor.

The boat is at a shop in Florida getting the once over. If I still have problems the next time I take it out, I will have to dig deeper.

I just don't know why the water pressure spiked so high with new impellers and South Florida salt water.

If it was before the pump, then you'd need a vaccum gauge, not a pressure gauge.

I have 496 Mags and want to install water pressure gauges. Does anyone know where I would tap into the system...

Thanks

Shhh!! its a secret..
You can tee in at the Cooler above the coupler. There should be a sensor there. Add a brass threaded tee.. Jamie / Lakeside

Thanks- I was going to ask the same question- do you rember what siz NPT? I'm guessing 1/4 or 3/8 but not sure would like to get the parts in one trip