250 SHO water pressure

[craisim]

I have a strange water pressure issue. I am running a 2011 Z521 ranger with a 250 SHO withabout 25 hrs on new power head. My water pressure gauge has never worked in the two years I have had the boat. The water pump was changed out by the dealership right before I bought the boat 2 years ago. I would like to have a pressure gauge even though I monitor my engine temp using my Lowrance.

I decided to dig into it. I replaced the Ranger transducer and my gauge checks good with a slight bit of air pressure. I have run the engine with the pressure line disconnected from the transducer and I am getting flow at idle. When pressure line is connected to to the transducer I get about 2-3 psi at idle.

Here is the strange part; As I increase speed and get up on the step the pressure bleeds off to zero and stays there even at 6000 rpm. The water temp is normal from 125 to 145 at idle to extended runs at high RPM. As I slow down to idle, I get the pressure back at 2-3 psi. I am getting the usual flow out the pee-hole at all speeds. Has anyone else experienced this? Any ideas?

[friogatto]

Your motor may be rigged differently but I thought SHO's have an optional water pressure sensor which sends readings digitally through the engine harness.

https://www.simyamaha.com/Water_Pres...a4l0-15-00.htm

[woppercatcher]

I don't have any electronic water pressure gauge but my pressure gauge that came with the boat never stays at the same pressure reading. It goes from say 8 to 15 over and over since I've had it. I have no idea why and can only hope this is not an issue.

[craisim]

I think I read a post where someone said that may be attributed to thermostats opening and closing. There is very little documentation that I could find showing a detailed schematic of the water pressure pathway. I have a Shop manual that is not much help either. I dont want to pay $180 for an electronic sensor but I may have to bite the bullet.

[Wackyjig]

A regular old mechanical gauge would do a better job than an electric with a transducer. When I got my sho my transducer sensor would read pegged to the top at anything over 3k. Got another one and it did the same thing.
I installed the sensor because I was doing trim and everything on a display on one of my console graphs.