Low water pressure issue. How to flush?

[RoughThumbBG]

I disagree. I rode around with the same motor height for well over a year and never had an issue. If the issue was solely the motor height, why did I not have an issue during that time?

Additionally, maybe "sucking air" is not the correct term, but the water pressure reading is measuring NET pressure far downstream of the intakes, which are essentially 3 different intakes all in Parallel (the nose cone, left side and right side.) I think we can agree that the lower the intake the higher the pressure. I realize they are not all equal and proportional but for simplicity sake lets say they are.

So, for example lets say I am running my engine as a given speed, trim, and motor height. With all 3 intakes full open and free of any blockages, I am seeing 20 psi. This is the net gauge pressure of all 3 intakes. If I were the measure the pressure at each of the intakes I may read 25 at the nose cone, but only 17.5 at each of the side intakes. Hence, averaging the 3 the NET pressure reads 20psi.

If I block off the nose cone completely and run at the same condition my water pressure will likely change, do you agree? Since I am getting 17.5 at each of the sides, and they are the only factors in the NET pressure reading, the NET pressure become 17.5 psi. The reading changed, but not due to motor height.

Lastly taking the same motor with the blocked off nose cone intakes and running it lower on the plate, my pressure will increase at the given speed and trim angle as before. Why? because the active intakes are lower getting a less aerated supply of water with higher velocity. Again the water pressure changed back to "normal" by lowering the motor, however the blocked off nose intakes are still present.

[EuropeanAM]

Brett... Respectfully, let's not waste time on this.

Savage is right- for SOME reason (reason not determined), your engine height was high enough to aerate the water supply (which is, in reality, from "sucking area through the water inlet openings").

Your activities proved this... very simply. Believe you've solved it... if there's not another problem, let's move on and invest some time in something that's broken or needs some help.

[RoughThumbBG]

I never meant any disrespect, and if I came off that way I apologize. I was just suspicious of that being the root issue. I really appreciate everyone's expertise on this board and that's why I look to you guys for help.



The bad news is that the problem came right back this weekend. I took the boat out and from the very first moment acted as it had before I changed anything. I was only getting a max if 17-18psi, trimmed all the way down at 45mph, and dropping to 7-10psi as I trimmed up to normal levels.

Water pressure is good at idle. Climbs up to 4.8-5.1 in neutral. Temps seem to operate well climbing to 127 and holding steady at both idle and speed (unless I am getting low WP, then starts to rise toward 140).

[RoughThumbBG]

Any other ideas before I bite the bullet and take it into the shop? Thanks in advance.

[Bob G.]

Choice #1: Buy the proper Mercury manual for your motor (based on serial number) and follow the advice given in this thread. Remove water pump and shift shaft carrier. Inspect water intake passages as Savage posted in post #6. Sounds dumb, but I'd make sure all water passages are below the bottom of the boat in clean water.

Choice #2: Take boat to dealer, explain problem and write check.

[RoughThumbBG]

I just realized that I never posted a follow up to removing the lower unit again and removing the shift carrier to check/clean out the passages for the low water pickups.

When i removed the carrier there was quite a bit of wood splinters and debris right at the inlets to the water pump housing, as well as some debris in the vertical section of the passage stuck around the pitot tube for the speedometer. The debris near the water pump as easily cleaned out and I used a piece of wire to clean out the passage way.

I took the boat back out and water pressure and temperatures are back to normal levels.



Thanks to everyone for the help on getting this figured out. I am going to add removing the shift carrier and clearing this passage out to my annual maintenance when I replace my water impeller. After looking at this, I am surprised this is not a more common problem with the way this is designed and how we fisherman use our equipment.

[Savage]

Post #6

[F150owner]

Does wood "shrink" when dried out vs being waterlogged? Just wondering if the blockage shrank from drying out and cleared.

[RoughThumbBG]

Does wood "shrink" when dried out vs being waterlogged? Just wondering if the blockage shrank from drying out and cleared.

I am sure some of it did, but when I pulled it apart there where pieces in there that were not getting out on their own.

[mdtritn21]

When you replaced your impeller in the water pump did you put in a whole water pump kit or just the impeller? If it was only the impeller put a whole kit in it next time.

[BIGFLAT]

I had a similar problem, unknown quick loss of water pressure, though the temperature indicator did not change. Atop my motor is the tap for my w/p which is 1/2" or larger , reducing down to whatever small size the tubing is going to the gauge. I had run thru some trash, and the trash got caught up in the reducer atop the motor. Might not be the same in your newer motor, but maybe worth a look see...BF

[Savage]

The OP's problem has been fixed......see post #46.