cdaniel525

iTrader: (1)

When the boat is idling Im getting a menial 1-3psi water pressure on a mechanical gauge at the helm.... However, once I get up higher in the RPM it really gets high..... and actually pins the 30psi gauge once over 4000RPM or so!
I am running a crossover style system with a bypass to the tstat housing (basically like the setup below) and fittings in the back of the intake manifold, into a "TEE" and to a thru hole fitting in the transom to act as a "tattle tale"
That said, this occurred on both my old motor last season and new current motor, so I dont presume its anything in the block....
And this started AFTER installing a new impeller kit and body on my engine mount raw water pump... The old impeller was intact FWIW, not missing any pieces.
I checked the gimbal/transom water inlet, not clogged.
All hoses not clogged
Oil cooler inlet screen not clogged

The only time I see a difference, is if I remove the TStat.... then the water pressures stay some what normal, if not maybe a lil low... Never does it seem like there isnt enough water getting through and cooling the motor.

Is it possible that the water bypass is fooling the TStat to stay closed almost always and then the "tattle tale" is flowing enough water to not allow the block to heat-up completely and the Tstat open as well.... and with the Tstat closed, the pressures are much higher? If so, I just wonder wjhy I never noticed it before the impeller change, unless the impeller was just worn out??

I should mention the Tstat is a 120* and it was same result with other Tstats, so I dont think this one is bad...

The only solutions I can think are:
1 - Run not Tstat, but just a water restrictor (but afraid itll never let the oil heat up?)
2 - Install a pressure relief valve like this...... http://www.keperf.com/p-976-water-pr...ve-12-npt.aspx

Thanks in advance for any ideas/suggestions!!



This is the style of crossover/tstat housing setup I have... not the exact one, but same principal...

[ATTACH=CONFIG]541978[/ATTACH]

BenPerfected

The increase in water pressure is affected by the speed of the boat and is it is not directly related to the RPM. My suggestion is to file off a about 1/16" off your water pick-up and see what it does to your max water pressure. We have our PU's set that even when running at 90 MPH the water pressure is only 10 PSI and the water temp is about 120. If we wanted the water temp higher, we would just add more restriction to the water flow. Engine cooling is about water flow not pressure. Also, the lower yours water PU's are the more speed you scrub. This right water PU depth could add as much as 2-4% to your top speed. We finally went to thru-hull water PU's and added another 1-2MPH. There is a lot of value in hull improvements vs. the $ it takes to add HP.

cdaniel525

iTrader: (1)

Thanks for the reply Ben.... I am running a stock Bravo 1 with the normal "high" water pickup.... lot the low water p/u I think you are talking about the style on the transom and/or thru-hull? I dont have anything like that unfortubnately... Mine is like the one in the pic below

[ATTACH=CONFIG]541979[/ATTACH]

fbc25el

Is there a divider in your thermostat housing to keep the cold water off the thermostat? I have a crossover system like yours. When I installed a Imco lower unit I had high water pressure.I installed a relief valve you showed in your picture. Works good I can put the pressure any where I want. Do you have any holes in your thermostat?

BenPerfected

Never tried this but wonder if you could just try a piece of tape or Bondo filler over a couple of water PU hole and see if that has any impact. There are numerous ways to bleed off water. an easy way is to water dump at the intake manifold, Besides the thru the bottom water PU flush with the bottom (no groove), we still bleed water at the intake. We use a 90 degree fitting at the intake and then use a drilled out threaded bushing inside the fitting to manage the water pressure.

cdaniel525

iTrader: (1)

Im not 100% sure, but will check next time I am at the boat... BUT i dont think there is a divider in there.... I dont think there are any holes in the TStat... no sure I can drill any either.... its a high-flow design and doesnt have those flat ledges like in most tstats.... pic below of what I have from CPP/KE/Hardin. Ill drill a few holes if possible though

My current setup is bleeding off water pressure at the rear of the intake... both the port and stbd side have fittings that combine into a "Tee" and then dump out the transom... Do you have a pic of your setup by any chance?




[ATTACH=CONFIG]541985[/ATTACH]

fbc25el

That's how mine are. You drill the holes in the vertical center part just above the flange part . 2-3/16 holes.

BenPerfected

[QUOTE=cdaniel525;4315128]Im not 100% sure, but will check next time I am at the boat... BUT i don't think there is a divider in there.... I don't think there are any holes in the TStat... no sure I can drill any either.... its a high-flow design and doesnt have those flat ledges like in most tstats.... pic below of what I have from CPP/KE/Hardin. Ill drill a few holes if possible though



Our current setup is bleeding off water pressure at the front of the intake... both the port and stb side have fittings that combine into a "Tee" and then dump out the transom... Do you have a pic of your setup by any chance?




The picture I have shows the -8 90 degree fitting in the front of the intake. We then have (2) -4 lines from the rear of the intake that tie into a small inline aluminum manifold to make sure there are no trapped air pockets in the rear of the intake.



[ATTACH=CONFIG]541994[/ATTACH]

1BIGJIM

iTrader: (1)

You are making this harder than it needs to be. Run a water pressure relief valve and be done with it. Holes in T-stat have nothing to do with pressure, I have two small holes in each t-stat and see 140-160 with a 140 t-stat.
.
I have a plastic merc valve with a small crack 1/4 long that sprayed a mist. I think it could be ground down and fixed. For $15 I will mail it to your door and you can try it. I even have pictures of the small crack. I run the ones from CP like you have shown. You need to get the pressure down, I never see over 25lbs on either engine at full throttle. And they dump water over 1,500 rpms out of gear....

Why did you change to a cross over?

minxguy

[QUOTE=1BIGJIM;4315400].
. And they dump water over 1,500 rpms out of gear....

Are you saying the mercury valves dump water? I hope that is what you are saying because I installed one on a 454/385 hp and water was flowing out the side at an idle.

Thought the spring was bad, Took the valve off the boat, but if this is normal, I will reinstall.

Ken