water pressure fluxuates on throttle 150 black max 1984

[cfcstl]

My engine is a mercury black max 150 1984. My last trip last year I was having water pressure and temperature issues and figured I needed a new impeller. Last week I replaced the impeller with a new kit and started it today for the first time. Water pressure seems good at idle around 12-13psi but when I give it some throttle, the pressure will start to climb then drop to about 5-6psi for a second then run back up. This seems like a new problem and I am not sure where to troubleshoot. I would like to take it out this weekend if I can fix the problem. Any suggestions would be helpful.

 

[Dave1027]

Re: water pressure fluxuates on throttle 150 black max 1984

Sounds like normal poppet valve operation. They usually pop open about 3k rpm.

 

[cfcstl]

Re: water pressure fluxuates on throttle 150 black max 1984

This is with a hose and muffler and nowhere near 3k rpm. At idle I see the 12psi then when I just begin to give it throttle around 1200rps I see a fast drop to 5-6 psi then it kicks back up. It will continue to jump around while I watch the water pressure gauge until I throttle back to idle. I wonder if the poppet is opening way to early and dropping pressure?

 

[jaylynd]

Re: water pressure fluxuates on throttle 150 black max 1984

test

 

[Silvertip]

Re: water pressure fluxuates on throttle 150 black max 1984

Using city water pressure to force feed the cooling system is not a valid test of the water pump. Splash the boat for your testing.

 

[cfcstl]

Re: water pressure fluxuates on throttle 150 black max 1984

Funny you should say that. My dealer wanted me to put the boat in the local river and check the water pressure too. I have been cranking my tap water full blast while running the engine and on one final test I only gave the faucet about half a turn and figured it was enough pressure and tested the psi. On that test I noticed there was no fluctuation! I then turned the water on full blast and the fluctuation came back. I am beginning to think the only problem was the water pressure from the hose. Everything I have done should be right and I am going to give it a shot at the lake this weekend.

 

[wired247]

Re: water pressure fluxuates on throttle 150 black max 1984

You cant feed your motors water pump with a water hose as fast as it will draw water. Your test isnt going to tell you anything you want to know unless you are in the water. With a new impeller on the water I usually see 5-15 PSI depending on sped and RPM

 

[jaylynd]

Re: water pressure fluxuates on throttle 150 black max 1984

test

 

[GA_Boater]

Re: water pressure fluxuates on throttle 150 black max 1984

jaylynd - What are you doing?

cfcstl - Muffs won't tell you much except water is flowing through the motor. And most the water from the hose squirts past the muffs with higher hose pressure. So yeah - dunk her as the others have said.