496 mag HO high water pressure... Help!!!
 

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? I'm trying to get this fixed so I can boat today!

did you back flush all the way out of the power steering cooler? i had a ton of stuff in there when my guage was reading high and pegged in the bottom.. Needless to say that the power steering is first in line and will probably be holding the most debris.

I can check the power steering cooler, but i don't think it has the honey comb deals to where it would clog up with anything. the oil cooler on the other hand does get junk in it, but it's hard to get to with it being on the port side on my daytona.
I'm still trying to figure out why i have so much pressure off my seapump?

if you haven't pulled the hose off the ps cooler that could be why you have the pressure. it does have the same honey comb design... the sea water pump pressure goes up as less water can get through. ps is the first culprit. your symptom is identical to mine.

of course, it's no guarantee. check it. it's cheap to do so.

Went and pulled hose on ps cooler and its nothing but a hollow tube, there's no honey comb in it. I knew there wasn't. Anyway, this is getting very frustrating. There's got to be some reason the seapump pressure is so high and blowing water out the pump out valve?? Hopefully Ray will shed some light on this??? I backflushed and have awesome flow, so I don't get it, unless it has something to do with the pump itself??

i have a stock system with the same type ps cooler as everything else on the boat and it was jammed. sorry yours is different. did you check to see if all the blades are on the impeller? they can cause issues where ever they happen to land if one comes off.

mine starts at ps and then oil cooler followed by cool fuel then on to heat exchanger.

Is this reading on a scan tool? I've run into this issue a couple of times with no real resolution. The PCM is showing high pressure, but it's not really high. Turn the key on with the engine not running and you still read 30+ psi. In my case it was always after having Whipple reprogram the pcm. I assumed it was a parameter that got altered in the process and never followed up on it. It's not the sending unit. We've replaced them. Maybe Dustin or Ray wil have some input. Put a mechanical guage on it to be sure of your pressure. If the pressure is really that high you probably have an exhaust blockage. I know Dana had this issue with there 496 manifolds originally and made some changes to correct it. You could try disconnecting the water hose at the manifold and start it for a couple of seconds and see if that relieves the pressure.

If it's off a pitot tube type gauge, don't worry about it. Probably a larger/smaller? diamater brass fitting off the raw water pump. I borke one of mine off a couple of years ago changing impellers. I went ot he local big box store and found a piece to replce it. Turns out it wasn't exact;ly the same diameter and suddenly started reading around 45-50psi on plane. Best part was it actually read while no-waking which gives me a the wram and fuzzy my impeller is working without having to wait to get on plane. May change out the other as well.

The reading is off my Mercruiser scan tool, which is picking up from the sending unit on the sea pump itself.

Yes, It's off my scan tool. I re-checked with key on but boat off and it read 31 psi?? What would cause this? Just a bad sending unit? That explains why one reads 3 psi at idle on hose and the other 34 psi. It's actually probably the same as the other one. Still trying to figure out why my dump valve keeps blowing off? I replaced it with a new one, so I'll see what happens this weekend.