nordic95

Hey guys I need some ideas here on how to lower my water pressure in my engines.I have two 502 engines with circulator water pumps still attached,CMI e-top exhaust manifolds and pretty a much stock water system.I run about 10 PSI at about 2500 RPMs then it starts to climb.AT 5400 rpms Im at 30 PSI.Now I have gone an added two Mercruiser pressure valves and they have not helped.I even lowered the spring pressure and tested them on the bench and they are fully open at 20 psi.Then I went and added 1/2" hose off the intake manifold and dumped that over board and no change.The only thing I could think is that the CMI's are to restricitve and not flowing enought water?Or my thermostat housing is not flowing properly?I also had duel water pick up drives and thought that might be the problem so I added nose cones and covered the lowers with no change.What else could I be doing wrong?I attached a picture of the thermostat housing that I am using.Anyone else use this type with any luck?

Thanks Anthony

1BIGJIM

iTrader: (1)

Where in the system is the water pressure being taken at?

nordic95

I am measruring pressure at the intake manifold,back side.This is after circulator pump.Could the circulator be building pressure in the block?I also just flowed my exhaust headers and they seam to have way more flow then expected.Still stumped!!!!

Nordic95

DareDevil

Usualy you take the pressure from the Thermostathousing,
U do not wan't more then 18 psi @WOT.
Maybe you need to check your pick up, buy the way what kind of pickup do you have Transom,thruhull or drive?


OH, are you shure your gauge is correct ?

nordic95

Standard water pickup in Bravo drive.I plugged low water pick up to help lower water presure but didnt make a change.

DareDevil

Do you have electric or mechanical gauge ?

nordic95

Mechanical and I just changed and installed new gauges and then I tested old ones and they were right on.

nordic95

Is it at all possible that the circulator pump could be build a little pressure while spining at 5400-5600 rpms???I thinking it is cause my merc dump is before the thermostat housing and if the pump could build pressure in the block while the thermostat is closed then that could be why Im reading high pressure but the dump is not opening.

Nordic95

DareDevil

I would try to take the thermostat out and run it without it.
Just to see if there is a diffrence.
Also i dont like those pumps any ways i prefer crossovers ,but i realy dont know right now what to tell you.
Keep us posted tho and we will get an answer in the OSO familie .

US1 Fountain

iTrader: (1)

I can't believe with the relief valve and the 1/2" intake dump you are still seeing that pressure, even if the t-stat is the hold up. Where are you dumping the water from the relief valve out? Is it a dedicated dump and is it the full 1" dump or did you reduce it down? I fail to see how the recirculating pump can build any pressure that you are seeing. (Maybe a couple psi??) It isn't a positive displacement pump, and can simply 'freewheel' with in the water. Dumb question, but you do have the valves plumbed up right? In your main 1 1/4" water line, before your t-stat housing with the 1" port your dump. (just covering all bases)

I'd also remove the stat and do a run. Might try the drilling the stat or using a restrictor plate instead, but with the relief valve, you should be fine. With the stat closed, the bypass circut within that housing might be too restrictive. Don't know, just thinking the same as the Merc 2 hose housing which is probably about the same as what you have.

Out of curiosity, when you see these high pressures, what are your engine temps?