Help- losing water pressure

[STELLIX]

I was wondering if someone could help me. I have a1996 Mercury 200 EFI with a Bob’s low water pick up on a small diameter ( smaller than the factory lower) coned lower. The motor is on a Hydrostream Vector with a 3” Slidemaster jack plate. The engine height is even or maybe slightly below the pad . I have about 2-3 psi at idle and a good stream from the tell tale and pressure increases up to about 15 psi at wot. My problem is I lose pressure if I’m up on plane just cruising 20 to 30 mph and the engine starts to heat up. If I slow down and get off plane it’ll cool down pretty quickly and if I increase speed to above around 40 mph it has pressure and cools good. I’m sure the boat is moving water away from the intake and it clears up as I speed up. Do I need to go up or down or maybe even back with the motor?

[Dave Strong]

Rebuild poppet. Sounds like weak spring or leaking diaphragm, happen right around when you reach 10psi?

Dave

[STELLIX]

Yeah, somewhere around there. I pulled thermostats and poppet and changed water pump. Everything looked good.

[Dave Strong]

Get a poppet rebuild kit, can guarantee the plastic washer on the diaphragm is warped or dished and spring could be getting weak.

Dave

[Jim Speros]

Is it possible at low speed on plane you have engine tucked all the way in and the intake is above available water?

[STELLIX]

Is it possible at low speed on plane you have engine tucked all the way in and the intake is above available water?

No, I thought about that but it does the same thing no matter the trim position.

[STELLIX]

The poppet makes sense. I just put this motor on the boat, my other motor didn’t do it but it did have lower water pressure though. My old motor was a 1993 XRI 150 and the new one is a 1996 200 EFI. I’m using the same lower unit on both motors. The 200 has a much better stream from the tell tale than the 150 did, the 150 would barely trickle out

[tlwjkw]

what do you mean by "heat up"??? how are you determining this??? do ya get a buzzer??? if its jus by a temp gauge it may not mean a thing....

[STELLIX]

what do you mean by "heat up"??? how are you determining this??? do ya get a buzzer??? if its jus by a temp gauge it may not mean a thing....

The temp gauge starts climbing pretty fast, if I speed up or slow down it starts coming back down pretty quickly

[STELLIX]

It acts like it’s not getting any water in that certain speed/rpm range

[Jim Speros]

Does your cone have hoses sticking out the side connecting cone to water passage? Have you checked them? Is hose obstructed? One hose or two?

Seems your at a speed where engine r's are low, so low pump action. And low speed with little force feed. You need pressure and flow. Maybe flow potential is low at low speed but force fed water at speed provides just enough.

When you serviced pump did you notice if the silicone strip between exhaust and pump housing was intact? Maybe exhaust pressure exceeds available water at that rpm.

Another thought extend piss [ Telltail ] tube forward where you can easily see it. It will be obvious if there is in fact no water at that speed.

[STELLIX]

It only has one hose, I took it off and there isn’t a blockage. I pulled the thermostats and put them in I pan of water on the stove and they are good and I pulled the poppet and it looks good. It never happened with my old motor with the same lower. This motor has a much better tell tale stream too