496 Mag HO high water pressure???
 

Recently I installed a new sea water pump assembly in a friends 496 HO. He ran it yesterday and now it's got 40 lbs of water pressure. Is this a dangerous situation for a 496?

(the old impeller did not lose any blades, the center hub spun)

Thanks,
Kurt

Re: 496 Mag HO high water pressure???
 

Normally when its that high it indicates a restiction after the pump, Id start by back flushing the system then check again if still high pull the end capa off of the heat exchanger and check then just keep checking the system there is a restriction some where


you can also check and see if the water rail modifcation was completed on it if not that could also be the problem

Re: 496 Mag HO high water pressure???
 

Is this at idle or wot or what? How are you measuring the pressure - Smartcraft gauge/monitor?

Dave

Re: 496 Mag HO high water pressure???
 

wot pressure is 40 psi. Smartcraft guage. Also has CMI headers.

Thanks for the replies.

Re: 496 Mag HO high water pressure???
 

At wot thats not as bad as I thought ( I thought you ment at idle) although at wot it should be beteewn 25-35 give or take so you are a little high should be about 7-9 at idle keep in mind these numbers are not written any where just from experiance

check for a restiction, what is it at idle ??????? what is it at idle when you pulll the lower manifold hoses ( do this only for a couple of secs )

Re: 496 Mag HO high water pressure???
 

We have seen higher pressures like this on new pumps with aftermarket exhausts. The Mercury water feed system routing and plumbing into the exhaust is excelllent in terms of not being restricted. If the raw water coolers are clear and the pressure is still this high he should be careful. The 496's have pressure relief valves in the raw water system and they seem to start blowing off into the bilge at about 4o -45 lbs of pressure. The scary situation here is that they sometimes get a little debris or stickyness when they open and at those pressures they can pump hundreds of gallons of water into a bilge in a very short time. So if you are at WOT at speed and noise level on a lenghty run, you could end up with a nearly swamed boat before you might catch the problem. We have installed the new CMI's on 496 engines and I am not a big fan of their raw side system mods for the 496 engine. I am not saying this is a restriction because we just build the motors, we don't do installs and the system is relativly new, but I would definitly try and bring that pressure down to the Mercury recommended system pressures.

Ray @ Raylar

Old thread, but I need help concerning this issue? My 496 mag HO is running 34 psi at the sea pump at idle hooked up to hose. The other one is running 3 psi. It's been mentioned that there might be a restriction after the pump, most likely the oil cooler, well I backflushed system and had excellent flow. The problem might still be partial blockage in the oil cooler, but I can't get to it on my 28 Daytona with it being on the port side. I also flushed out the heat exchanger. Any ideas on why psi is so high and causing drain valve to pop open and fill the bilge at higher speeds?