Cooling H2O Pressure

[BaldEagle]

I've briefly looked through manuals for guidlines of minimum cooling h2o pressure for various speeds but havent found any data. This would be the hydrostatic pressure from the velocity of the boat through the water that provides either the cooling water to the engine block or to the HX in a closed loop system. Any one have any information on this?

[MOP]

There have been some very good discussions up on OSO about the pressures developed and the problems it can cause, I ran into a problem when I switched from the Blackhawk drive to the dual pickup Bravo X. I developed a mystery water leak into the bilge, it turned out to be my sea strainer cap I changed out the gasket to another type of rubber and cranked it down harder. Big Griz stated that the pressure can rise to close to 100 psi at high speed faster then I go, Merc sells a relief valve to dump anything over 30 psi. Even 30 is relatively high compared to the auto industry which runs about 14 psi, the high pressure can do a couple of things like make head gaskets weep and blow hoses. I did several thousand sea trials on boats while I was on the wrenches and it always amazed my to see how much the circ hose expands as speed increases. I would say if you are running 75 or better install a relief valve, there are alternatives the near $300 plastic Merc valve. Stra Valve for one solid SS and bronze under $100 but a few others were mentioned on the other site, go up there and do a search there is a ton of info.

Phil

[gcarter]

This is a quote from Brownie;

"Formula for ram pressure (Speedometer pitot pressure). V squared X .0147= psi. V is speed in statute mph, Thus, water pressure at 30 mph = 13.23 psi. 100 mph = 147 psi., 200 mph = 588 psi. Holy chit! Same could hold true for cooling water pickup. Hmmm........"

:)

[BaldEagle]

I appreciate that the presurre varies as a square of the velocity however what should the minimum pressure be. Or is the answer is it doesnt matter as long as the H2O discharge temp is 160-170F. Is there a throttling valve to control discharge H2O temp, (H2O flow through the HX or block), or does it run free?

[gcarter]

The only restriction on mine is the P/S cooler, oil cooler, and HX. It runs wide open.
It also operates very well. I usae a transom pickup and a crank driven Johnson seawater pump and I've often thought the S/W pump might become a restriction at speed and I've considered running a bypass spring loaded checkvalve around the S/W pump. That could well be an interesting experiment.

[MOP]

George Randy was talking about a transom pickup and just how much pressure they can build, I could run my SK boat without the raw water pump as long as I got it up to a good speed before it got hot. I found that out when my pump let go one day, I pulled the impeller, cleaned out the rubber from the oil cooler and put the cover back on and made it back to my creek and bummed a tow to my dock.

[MOP]

George if you go with a relief valve put it in just after the strainer before the pump that will relive the whole system.

[BaldEagle]

I'm going to look at mine. Its a 05 and I thought the pickups in the drive unit just pressurized the HX closed loop cooling system. Im not even sure if there is a separate oil cooling, or P/S cooling HX. In any case I agree with MOP to make a bypass effective it should be located upstream of the pump, which means thats where the sensor would have to be located.

[BaldEagle]

GC
is your cooling system for the eingine, P/S, Oil, HXs in series or Parallel in the S/W cooling H2O circuit? I should have asked, but my S/W pickup is in the lower part of BravoX drive. I Think thats what I'm looking at.

[conyo]

Hey just a thought, since the H20 exits the system through the risers with exhaust flow. Wouldn't the exhaust create a vaccum it the system or at least lower the pressure? Same principle as a aspirator vaccum! I'm gonna install a pressure gauge on my strainer to see what kinda pressure I get...sorry I max out at 80kph:garfield:

[BigGrizzly]

Yes water pressure can rise to 100 psi on re entry. The fact is anything above 35psi can cause problems on raw water systems especially on blower motors. on closed cooling systems it isn't such a big issue. Stainles marine sea strainers have a port for the pressure releif valve, Bronnie can hook you up. Have you ever noticed on some engines there are rust marks on the block starting from the head gasket going down. High water pressure causes this. I have seen head gaskets blow because of it. O a closed cooling system the only thing that happens is a blown gasket in the sea strainer or a hose or a gasket on the heat exchanger.

[gcarter]

GC
is your cooling system for the eingine, P/S, Oil, HXs in series or Parallel in the S/W cooling H2O circuit? I should have asked, but my S/W pickup is in the lower part of BravoX drive. I Think thats what I'm looking at.
It's in series. I even included a shut off valve in case of emergencies.
So, the list goes like this;
transom pickup
shut off valve
sea strainer
Johnson S/W pump
P/S cooler
Oil cooler
H/X
risers
If I were to include a bypass, not a relief valve, it would run between the sea strainer exit and the P/S cooler inlet and include a bronze 1/2 # spring operated check valve. At speed, the water flow would tend to go through the bypass and not so much through the pump, eliminating a potential obstruction.

[MOP]

George why do you consider the sea pump to be a restriction? It in a way helps to reduce the incoming pressure which is good, in tech school they had a sea pump with a clear cover to demonstrate how the vanes reacted under pressure. They would close a valve slowly as the pressure rose in the system the vanes tips would bend clear of the housing relieving the flow, so if the incoming pressure rises above the system pressure then the vanes would contact the housing to some what reduce the pressure would it not. I believe the object is to reduce the pressure, even on CC like we both run the hoses are under great pressure at high speed. I took that into consideration and used all wire wound Perelli hoses in the raw side so as not to worry about the possibility of popping one.

Phil

[BaldEagle]

Now I'm wondering what the water pressure guage on the dash is actually indicating. Pressure is very low at idle speed so if the pressure sensor is on the suction side of the S/W pump it would be measuring only the pressure from the drive pickup to the pump suction, less any suction head the pump developes, which may be none, but it would not be indicating pump discharge head or pressure on the HXs. Is the pump gear/belt driven or electric single speed? It would seem as long as there was enough pressure on the pump suction to keep it flooded that the rest of the S/W flow could bypass everything.

[BaldEagle]

At idle speeds a couple lbs. At 55-70 in the 20-30 psig range. Of course at those speeds I usually have the frive trimmed up too. I'm going to look to see where the pressure sensor is this weekend and also how it is circuited. I started wonder aoout this b ecause I thought I noticed a reduction in pressure and was thinking I had a blockage. Then I starte dlooking for some guidlines for the correct pressures I shoud be getting at some baseline speed.

[yeller]

At idle speeds a couple lbs. At 55-70 in the 20-30 psig range.
I've also wondered about my pressure (496HO). At idle, it's like BE's (couple of lbs). At 5000rpm......well gauge goes to 35psi, but needle goes far beyond that. :confused:

BTW: BE, I like your signature. :wink:

[BaldEagle]

Yeller, I'm working on the signature project. I wont have a chance to look at my cW circuit until latter this week. We got sruck by lightening on Fri night o I'm still scrambling to get phone, well water, boiler, internet and others back working. I'll let you know what I find on my 22 496HO.

[tom freeman]

[QUOTE=BigGrizzly;387318]Yes water pressure can rise to 100 psi on re entry. The fact is anything above 35psi can cause problems on raw water systems especially on blower motors. on closed cooling systems it isn't such a big issue. Stainles marine sea strainers have a port for the pressure releif valve, Bronnie can hook you up. Have you ever noticed on some engines there are rust marks on the block starting from the head gasket going down. High water pressure causes this. I have seen head gaskets blow because of it. O a closed cooling system the only thing that happens is a blown gasket in the sea strainer or a hose or a gasket on the heat exchanger.[/QUOTE

my corsican is running great!... the transom pick up is atached to stainless valves and pipes... then into a strainer. i ran at 147 degrees all day.

how and what do i need to add now to insure i do not have too much pressure? gauge...relief valve?? where do i get them?

also i filled the strainer with seaweed in one day, and to think i was not going to add it in the system. should the transom PU have a screen of sorts?\:lookaroun:

[LKSD]

At idle speeds a couple lbs. At 55-70 in the 20-30 psig range. Of course at those speeds I usually have the frive trimmed up too. I'm going to look to see where the pressure sensor is this weekend and also how it is circuited. I started wonder aoout this b ecause I thought I noticed a reduction in pressure and was thinking I had a blockage. Then I starte dlooking for some guidlines for the correct pressures I shoud be getting at some baseline speed.

These pressures you have seem to be about average.. :) J

[LKSD]

The only restriction on mine is the P/S cooler, oil cooler, and HX. It runs wide open.
It also operates very well. I usae a transom pickup and a crank driven Johnson seawater pump and I've often thought the S/W pump might become a restriction at speed and I've considered running a bypass spring loaded checkvalve around the S/W pump. That could well be an interesting experiment.


Actually the sea water pump can slow down the water pressure to a certain extent on some really fast boats. It can actually be a good thing because it can aid in keeping it from over pressurizing the system. J

[tom freeman]

my questions are:

on a transom intake system

do i need a water pressure guage on my intake and if so where do i install it and where do i get it?

also on a transom pick up does anyone have a screen on the intake to keep out weeds.

[gcarter]

my questions are:
on a transom intake system
do i need a water pressure guage on my intake and if so where do i install it and where do i get it?
also on a transom pick up does anyone have a screen on the intake to keep out weeds.
You don't want a screen...it will get clogged very rapidly. Let the strainer do it's job.
Someone mentioned Stainless Marine has a relief valve. If you use one, install it after the strainer. If you discharge the relief valve straight out the bilge pump discharge, and install a TEE with the branch mounted vertically, discharge the bilge pump through the TEE branch and you probably won't have any water go back down the bilge pump line. Or you can add a seperate discharge through hull fitting. With a relief velve installed, you won't need a pressure gauge, unless you want to add some more bling to your dash.

[tom freeman]

thankx GC
i am not into anything more on the dash.
do you think i need the release valve

and if so is there a pressure platau or setting.

if you do then i will call the stainless folks

[gcarter]

thankx GC
i am not into anything more on the dash.
do you think i need the release valve
and if so is there a pressure platau or setting.
if you do then i will call the stainless folks
I didn't have one on the Minx...for about a year everything held the pressure (mind you, I had closed cooling so the water just went through all te coolers) but eventually it started leaking somewhere...I never did find the leak. I would dump 4-5 gallons every time I recovered the boat. It only leaked while underway. I could have used the relief valve.

[BigGrizzly]

Let me clarify the water pressure issue. You 496 guys don't have to worry. The problem is mainly for the raw water system guys. The thermo-shock and added pressure to the cylinder head gaskets on mainly crossover and other raw water systems. This is one small reason I took off my crossover off and went to closed cooling. The other reason is I don't like salt or high calcium water in my cooling system. I like the rust inhibitors i n antifreeze. No more in that I don't want to hijack the thread.