Optimax 115 Low Water Pressure/Mounting Height

[ChrisPage227]

I bought a reman'ed 2008 115 Optimax for my 17.5' Procraft fish and ski and taken it out a few times to run through the break-in and ran into an issue with low water pressure. I have a system monitor gauge on the boat to read water pressure direct off the sensor. The SN for the motor is 1115D73HY.

At idle the water pressure is in the 3-4 PSI range. And when i ease into the throttle to get up on plane the water pressure increases and maxes out at about 10PSI at around 3,000RPM. I am getting that pressure right before the boat pulls up on plane, so it is really dug into and planted in the water in this moment. Once it is up on plane the water pressure is in the 7-8 PSI range. The first time I took the boat out with the new engine as soon as the system monitor gauge threw the low water pressure warning symbol on the gauge I used the trolling motor back to shore and pulled the leg to see if the water pump was screwed up somehow. It seemed fine but and the impeller looked new as I would have expected but I replaced it and the water pump gaskets since I had it opened up. Took the boat out again a week later, exact same situation, 3-4 PSi at idle, up to 10 PSI at around 3000RPM while still not on plane, and around 7-8 on plane.

Took it out one more time to check the tubing from the block to the water sensor and where it is tee'd off and plugged for adding an analog water pressure gauge and didn't see any leaks.

I have been monitoring the temp during these tests and seeing what I would expect, temp in the 120-130 range if it has run an second and I am going slow around the ramp or a kayaker, but when i am able to run it the temp came down to the high 90's, so it seems like the thermostats are working.

Based on what I have seen I am wondering if I need to have the motor mounted a bit lower. I am one hole above the lowest mounting position at the moment. One this engine it kind of looks like there are two anti-ventilation plates and the lower one, which I believe is actually the anti-ventilation plate, is set for about 1" above the lowest surface of the bottom of the center of the boat. And when I had it on plane that lower plate was submerged, and the plate above it, I suppose this may actually be the anti-ventilation plate, was about 1/2"-1" above the water surface. That plate is the plate I circled in red in the attached photo.

Plate.jpg

20200530_085251.jpg

I am going to lower the motor down to the lowest hole to see if getting the intake holes down in the water lower will resolve this. It seems like the engine is cooling as it should theoretically, but I really haven't run it much considering I am trying to break it in and dont want to do it with a question about the water pressure.

Any insight on what I could be missing or what I should check form here would be much appreciated.

[JOE54]

nothing mounted on boat bottom in front of gearcase to obstruck water flow is there ???//

[ChrisPage227]

nothing mounted on boat bottom in front of gearcase to obstruck water flow is there ???//

Nope. Transducer is well off to the side, it's about 12" to the right of the motor roughly.

[JOE54]

you could try moving it down but it doesn't look high too me from pics get in boat forms like yours and see where others have theirs mounted and what prop that block has a poppet and thermostat in small cover back of water jacket

[ChrisPage227]

I just searched through the Procraft forums, didn't find anything relevant. I really thought I had the height set right but I will find out in a few hours. If lowering down a hole doesn't impact the symptoms in any way I wonder what direction to go in next. Could the water pressure sensor be bad and causing this?It doesn't seem to be overheating at all with this water pressure range I am getting but at the same time I haven't run it for more than a couple of minutes at a time because it isn't really broken in yet. I thought about adding a regular old analog water pressure gauge at the end of the tee'd off grey line from the block to confirm the reading from the sensor was accurate.

When I had the leg off to inspect/replace the impeller and gaskets on the water pump I did look in the passages from the intake holes on the front of the lower unit and that all looks clear as can be. I didn't replace the water pump housing and wear plate. They seems perfectly fine but that may have been shortsighted Given how they looked though I am suspect that they are the cause of the problem.

[JOE54]

analog sure would tell , and complete kit would elim any possible w/p problem

[ChrisPage227]

I did take the boat out again in the new lowered mounting position to to eliminate the variable of mounting height from the equation. It did not change anything, had the same water pressure as previously reported (7-8psi at 4,000RPM running on plane). I guess at this point I will replace the whole water pump (housing and wear plate) and see what happens. Could this be a water pressure sensor failure mode? I would find it hard to believe that the sensor works out at lower RPM and not at higher RPM so I don't think that is it. I would guess those either work or don't.