ALL_IN!

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.

PARADOX

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.

jbraun2828

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

PARADOX

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.

Brembofreak

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

HyFive578

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.

Brembofreak

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

HyFive578

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.

Brembofreak

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

PARADOX

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.