Water preassure in Bravo XR?
 

Long story, short version. I had low water pressure on sensor some months ago. Not the sensor. Checked all hoses, OK. impeller is new. etc. So I bypassed the outdrive intake and did a temp, external water pick up. Water pressure is back, but it's actually higher then coming through the drive. I know with the speed. 50-60 MPH there is water forced into the tubs/ pipes but I'm getting 30-38 PSI at 4000+- RPM. Is this OK? with external pick ups? Apparently my low water issue is due to the hose or the 90 deg pipe in the drive and the transom. I know the damn part. I don't even want to mess with it so I'm thinking putting in external water pick ups but just want to make sure the pressure with them is in the normal range.
Thx
P

With closed cooling it is OK. With raw water too high.

It's closed cooling, and 525's. EFI. I'm asking about the raw water (sea water) pressure.

Is still try to get it lower. Not as detrimental as if it were open cooling but still not ideal. The high pressure could actually be a sign of the water backing up in the system and not getting out fast enough causing temps to rise. Again not as much of an issue with closed cooling but I'd rather see it around 20

With the bypass, external water pick up, temp is good. Both motors been running around 25-28 at higher RPM's with water from the outdrive. With this make shift by pass, and checked ALL the hoses, coolers, there is no restrictions. Temp is good with the bypass. Temp got to 165's when I had the water coming through the drive, so I know something was up. Merc.'s guess was that I have a leak and getting air in the system at that darn tube at the transom. They were right. I had air bubbles when I put in a plastic tube. With the bypass, everything is good but pressure is up.

That pressure does seem a bit high. Maybe the external pickup is too wide and you are getting too much water volume compared to what comes in through the drive causing the higher pressure. If the pressure climbs too much you could start to see leakage at the seal in the sea water pump housing.

Good point. My temporary pick up, is 1" IS diam tube ( made a 45deg cut in it so yes, it an get a lot of water) into 1 1/4" rigid rubber tube into the impeller housing. Just like the outdrive system, but the 1" pick up might be too big. I know the drive little tube is smaller. (3/4" ? )

I'm not sure of the exact size, but I'm pretty sure the water hose between the pickup holes in the drive and the fitting in the transom that the 1 1/4" hose connects to is less than 1" ID. I bet your pickup is just a little too big...

the depth that the pickup enters into the water plays a big part in water pressure.can you raise the pickup one quarter inch?

Totally stumped on this one guys.
With the temp external pick ups pressure went up. may be a ted high, but it went up. So.. before I start drilling holes and install external pick ups as a permanent set up, I changed the drive inlet tubes from Port to Starboard. Thinking... if the issue is in the drive, then the Port drive should loose pressure. (Starboard was loosing prior) Sucking water from the Port drive (extended the intake hoses) Starboard pressure is still low. Port is OK. THus the outdrive hoses, etc are ok. All the engine hoses been removed and checked. Oil cooler; clean. Front heat exchanger; clean. Any thoughts why my water pressure could be low? HEEEEELP. :) Impeller is new. Rotation correct.

While we've got different engines and cooling systems, this sounds very similar to my issue....

http://www.offshoreonly.com/forums/d...tml?highlight=

As you can read there, I was down in the 3~5 psi range at cruise speed - an only increased by another 3~4 psi at WOT. Not good enough.

I never did get to the bottom of it. But while the engines were out getting top ends refreshed, Eddie Young plugged the top 2 holes in the upper DWP drive and scalloped the bottom 3 holes to grab more water. I haven't had the boat out, but he said water pressure increased to allowable range. Merc had a bulletin out about plugging the holes, but I didn't think it was applicable to my application. Evidently, it does work - so that is something you might want to try. My water pressure was good when I first got the boat (2 years ago), and it slowly started going away.

I had no pressure problems for 5 years, and I have the XR shorties with low water pick up. If there is any "restriction" anywhere past the pressure sensor the reading would be high, not low. Assumingly, I either sucking air, or something else is up, but changing the Port lines to Starboard, sucking air is out.

Sea strainer not sealing? Also you changed impeller, did you replace housing as well?

Housing replaced also. Good try with the strainers. lol, but I by passed it for all the testing. The only thing left is the fuel cooler, but I didn't think that would clog since it has no small holes in it, like the oil cooler. Besides water flows through it easily, and I can blow air easily too.

I just read your thread Easy, I doubt it's my fuel cooler, but I hope it is. However, I'm a bit at ease knowing I'm not the only one chasing low WP. :) My gets to 7-8 at higher RPM's. Temp, creeps up to about 170 may be 170+.Not about to go WOT yet.

Hello
I am not shure,but at newer engines the seawaterpressure is not real high with closed cooling system!!
i have the new 8.2 Mag Ho in and smartcraft gauges!
Highest Pressure can be under 12 PSI be! To get 100% performance from engine the pressure need only be 11,75 PSI.
My engine is in this range and there are no problems at all!
I was also first wondering about this low pressure,but i have now a list from merc what pressure engine needs!
Bets regards, Michael

I doubt its the fuel cooler but its pretty easy to check. You may have said this already, but have you back-flushed the entire system? ie: all of the coolers and the heat exchanger and both headers?

I know you said it was not the water pressure sensor, but how do you know that? Have you tried swapping the water pressure sensors on both engines? Also, the nipple on those sensors are pretty small, are you sure its not clogged? If you haven't done so, swap the sensors and see if it follows the sensor.. Also try swapping the leads to the gauges and see if it stays with the gauge.

Do not be at ease with the low pressure just because someone else has the problem. You need to fix it for sure or you risk killing those 525 headers. Low water pressure is the worse thing thing for them..

I would also try spraying the sea water pump housing with some soapy water and see if you have an air leak there.

I take a look at the Merc list for newer engines with closed cooling! for 100% power you need only seawaterpressure over 11,46 PSI and under 12 PSI!
this is fact and i am sorry that i can not upload the picture from list here!
Waterpressure is complet diffrent to older modells with only seawatercooling! you dont need over 12 PSI!
Sensor for seawaterpressure in after seawaterpump in the steeringoilcooler!
Michael

On 525's, you should see sea water pressure between 4 and 8 psi at idle. Between 20 and 30 psi at cruise speed between 3000 and 4000 RPM and between 30-35 above that... You may need less pressure to keep the engine performing, but less than this and you will starve the headers for cooling water and on the 525's, that is VERY bad. The fact that the OP has a difference in pressure between his two motors is an indication that there IS a problem.

This can be!
And also i am not shure where the 525 takes the pressure!
My sensor is after Seawaterpump in the steeringoilcooler and it was shown at a smartcraft gauge.My engine is exact in this range and will not show more at this point as 12 PSI.
If you look on the Smartcraft gauges that are sold from Merc,they only can show max 30 Psi!
There must be any diffrences in the way of mess waterpressure between newer smartcraft gauges and older maybe analog gauges!
I get the list with pressure from Dustin Whipple and he say that ist standart!
Michael

Flushed the heII out of it, backwards, forward, removed all hoses, removed the plates from both coolers, used a thin stainless rod to clean all the holes, etc. Nothing there. The sensor is good since the pressure came up with the temp, outside intake bypassing the drive. PLus I got the vessel view, so the connections are different. Switching intake hoses from Port to Starboard also showed that there is no issue with the drive tubes and intakes. The problem remained in the same motor. I will try the soap around the impeller housing. There isn't much else possible. I'm not at "ease', just relived a bit that others had this WP gremlin too. But the impeller and housing is new. I changed them at the first sign of low WP. THis is a head scratcher. :(

I know the story about the low water presser on my engine now!
There are diffrent sensors for the PCM (this is psi what smartcraft show) and for the analog gauges!
There is an higher pressure shown!
The engine can have min 17 Psi max 41 PSI at WOT to get no damage!
You hope you can sometimes close your problem.
michael

OK. I'm going to rule out the results you get with the external pickup because I think the force of the water entering that pickup is what is driving the pressure up so that is somewhat of a false reading. I think if you add an external pickup, you're going to be masking a problem that you really should solve.

You've already ruled out the drives so that's good and you say that all of the coolers are clear. I'm running out of ideas but the next one I have is to check EVERY single hose in the system, not for obstructions but for cracks especially around the area of the hose clamps. A tiny crack would not likely show up when you're flushing or running the engine, but might just suck air under the suction of the sea pump. Try plugging one end of each hose and then pressurize with 20-30 psi of compressed air (you may need to get a few fittings), submerge in water and look for bubbles.

THanks for your input. The external temporary water pick up was an attempt to locate the problem. Since the pressure goes up, the sensor is ok and works. The only air incoming leak I might have is in hoses under negative pressure/suction. All the hoses under positive pressure while it might reduce the reading WP, they don't leak. No water or even any seepage. I'm down to impeller, housing or a f'up vessel view read out. But the temp does creep up a bit, so I'm ruling out the vessel view read out. It might be as simple as having the hose to the intake side of the housing too tight. GGGRrrr stupid me, but I hope that's all it is. ( I use the T clamps) It's possible that I cracked the housing tube by over tightening. In that case I will feel pretty silly, but will post and go hide somewhere.

I'd be pulling the impeller housing back apart, make sure no issues there.
Hoses oriented correctly I assume.

temp creeping up = no good. good luck and please post what you find... even if it is embarrasing...we've all done it..

I had exact same problem last spring. Working backwards.. It was the last hose I checked. The hose in the bell housing became a little twisted some how. I just removed the plastic insert and straitened the hose replaced new insert and all worked fine all summer. Simple problems like this drive you crazy!

Might want to drain and back flush your block as well. Could be some of the small holes in the head gasket stopped up.

How were you able to determine that the hose was twisted? I've looked at mine (with drive installed), and it doesn't look twisted, but not sure I can tell with drive installed.

Thanks.

Did you replace the hard-walled hose between sea water pump and water neck at the transom? I've heard that they can delaminate inside and suck closed. I replaced mine but unfortunately, it had no effect.

525's are closed cooling. Nothing to do with sea water pressure.
1BIGJIM. I swapped the drive intake lines from Port to Starboard. The issue remains, nothing to do with drives or hoses from the drive.

I missed that on the quick read thru, sorry.

No biggie, all this is info only. It's all good. :)

I put a hose with a straight nozzle in the hose off sea water pump to out drive to flush it. I noticed water was not going out as fast as it should have hence blockage. That hose can also collapse from suction if it's to soft.

OK.. I did some more "stuff".. :) Let you guys know after a little test run in a few days.

I've seen the inside of perfectly good appearing hoses delaminate , fluid will go inside the delamination and bulge inwards .Effectively blocking the hose ,causing a restriction , either suction or pressure .
The Hydraulic guys call it a Flapper.

Since I swapped intake lines from side to side, the hose is not an issue. (read above)

After another new impeller and housing, checked ALL the hoses, (clear) checked the oil cooler ports, (clear) fuel cooler ports, (clear) heat exchanger ports, (clear) restrictor at the headers, (clear) still have low water pressure. Rigged a temp. external water pick up, (by passing the outdrive) pressure is good but at 60 MPH. 4000 RPM it hits 40 PSI. Too high. I am totally stumped. Any other ideas?

40 psi is within specs for a 525. The manual says max is 43psi and I know of one person who regularly sees 60 psi.

Earlier post referenced that 40+- PSI is too high. If I don't have to worry about the 40PSI with direct water intake, (eliminating the outdrive intake, and allowing the water to be forced in) I'm ok. But.. here is the "but" if the direct water intake goes to 40 psi, that shows a restriction to me. There is NO restriction before the sensor. If there is some restriction after the oil cooler, wouldn't that show a "high pressure" ? instead of low?

This must be incredibly frustrating. I know you've tried a lot of things already, but there has to be something you're missing. If you go with the direct water pickup, you're treating the symptom. Do you have a sea strainer? Have you tried bypassing the strainer but still pulling from the drive? Maybe there is an air leak there. Does your strainer have a relief valve? Maybe that has failed and is allowing air in which is bleeding off suction. Have you tried swapping the water pressure sensors on the engines to see if the problem follows or stays with the engine ? Are you sure the core of the heat exchanger is unclogged?

Yes, yes, and yesss,, lol. But thanks. Sea strainer is bypassed for now. Already swapped port to starboard drive intake, (extended the hoses and drawing water from port to starboard, problem remains with starboard drive. Sensors been swapped. Getting 40+ PSI with the direct intake shows that the sensor works. Backflushing from the headers connecting hose (last point of restriction) water flows freely. I'm stumped . I just hope some one tells me what I'm not seeing yet, or didn't try. There got to be something somewhere. GGGGRRrrrr.