496HO & Water Pressure
 

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.)

Re: 496HO & Water Pressure
 

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

Re: 496HO & Water Pressure
 

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.

Re: 496HO & Water Pressure
 

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

Re: 496HO & Water Pressure
 

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???

Re: 496HO & Water Pressure
 

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.

Re: 496HO & Water Pressure
 

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

Re: 496HO & Water Pressure
 

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

Thanks

Re: 496HO & Water Pressure
 

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

Re: 496HO & Water Pressure
 

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:)

Re: 496HO & Water Pressure
 

Dont quote me on it, but believe it is 1/4"..

I just grabbed some more T's As I also needed one for my boat. I had some that were to big in our parts room & for some reason I'm thinking they were 3/8" and that's why I had to get the 1/4" ones.....

If you cant find what you need locally, call me I can set you up with the t's that will work for you.. :)

:) Jamie / Lakeside 570-639-2628

Re: 496HO & Water Pressure
 

Smart a$$...:D :D

Re: 496HO & Water Pressure
 

A little friendly teasing never hurt anybody.. :) Jamie

Re: 496HO & Water Pressure
 

Mine are pitot tube style on my 496's. There's a brass fitting on the body of the raw water pump with a tube running to the gauges on the dash. Typically reads 30-35 psi. They're very fragile though. 2 years ago went to make my first impeller changes and broke one off. Went to Home Depot and found a similar fitting though it's either more narrow, or wider bacause the pressure now reads in the 40's. This past year same routine only on the other side. Nowe both "read" higher pressures coming off the pump not from the system. So it's the fitting giving a false higher read. Don't care personally.

My point is if you had this pitot tube coming off your pump you may have slightly bent it creating both a fracture to spray water in the bilge, and to pinch it enough to make the gauge read higher. I'm not familiar with the mechanicals or the ones mounted above the coupler area. Just a tickler thought.

Re: 496HO & Water Pressure
 

Brian, The pressure is read as it enters the SWP, most likely your heat exchanger gaskets are falling apart and the heat exchangers are getting partially clogged/blocked. If you want pm me your number and I'll explain it. Its really pretty simple buy some 1/8" cork and make your own gaskets and use a coat hanger and some compressed air to clean out the heat exchangers and your pressure should come down. I have had some pressure issues with my 496's as well for some reason one motor makes twice the pressure of the other.