1994 mercury 75hp water pressure

[lostinboat]

hi, I have a 94 mercury 75hp that has been running about 5psi water pressure at idle. at 3500 rpm i get about 10 psi, If I raise the rpm's above 3500 rpm's my water pressure drops to around 4psi until i lower the rpm's back to 3500 or less and then jumps back to 10 psi. this has just started as this engine has always run at about 12 psi at 5500rpm's. Could this be the water pump going? pee stream is strong. engine temp runs at 146 degrees Thanks for any help.

 

[1nebel0]

Re: 1994 mercury 75hp water pressure

Your pressure numbers are good but what an odd situation.. Keep in mind that the poppit valve opens around 2500 and your pressure will drop for a moment and then climb back up after the valve has opened...At this point I would check the poppit valve just to eliminate that...The rpm's that your problem is happening is strange and the fact that the pressure doesn't build back up is a strange one...Hope someone else chimes in on this one..Is the impeller new and could the hub be "spun"...(long shot)

 

[lostinboat]

Re: 1994 mercury 75hp water pressure

replaced poppet valve diaph. and thermostat. Am planning on water test this weekend, hopefully solved problem. will post results after. Thanks for help.

 

[lostinboat]

Re: 1994 mercury 75hp water pressure

problem solved, Bad diaph. in prv. water pressure where it is good now and steady. thanks for all the help