Water pressure

[Calabrio]

I just had the water pump replaced on my 150hp Mercury. <br /><br />The stream of water coming out the top of the engine is pretty weak. But, I'm turning pretty high pressure numbers while running the boat. Idle is around 2lbs though. <br /><br />The last owner said that he'd bipassed something so that the valve was always opened, and the engine always circulated water through the powerhead. Living in Florida, I have no need to worry about cold engines. <br /><br />Should I be concerned about this week stream of water? Also, I saw a trickle of smoke come out of the square exhaust ports after I flushed the motor in my driveway. The casing on the lower unit was warm too.<br /><br />Should I be alarmed?

 

[KCLOST]

Re: Water pressure

That valve would be the poppet valve, (or high pressure relief valve). If it is always open, that is why your pressure is so low during low RPM's...And probably a reason for the casing to be warm... When the poppet valve is open more water is allowed to exit through the exhaust... When the valve is open the pressure drops through the entire cooling system, but you would normally have much more flow to compensate... IT SHOULD ONLY OPEN AT HIGH RPMs.. Otherwise you may allow the water to exit the motor before it circulates though the entire system, heads, stats, etc. (while you are at low RPM's anyway). It is a cheap part, easy to put back in. He probably just pulled the spring and plug out...

 

[Ray 2000]

Re: Water pressure

I just installed a new water pressure gauge on my Ranger for the 1999 Mercury EFI 150hp The pressure seemed low to me so I called Merc. to get some advice. Mercury faxed me specifcations.<br />Nothing until warmed up then: Idle 1 to 3 psi. Poppet valve opening 4 to 9 psi and wide open 12 psi. The engine is designed that the pisser stream comes out AFTER it's gone though the block & motor and will have no pisser stream until termostat opens up.<br />Just passing along the info so nobody else needs to worry.

 

[Calabrio]

Re: Water pressure

I'm seeing pretty high pressure readings on my water pressure gauge. I remember seeing it running as high as 20lbs at throttle.<br /><br />Should I be alarmed?

 

[KCLOST]

Re: Water pressure

Calabrio,<br /><br />Here is a post from Trumanlake, who helped me with a topic I had a while back.<br /><br />This is not from a book, just his observation, but it makes sense. He has a 1987 Merc. 200... If you have a mid 80's Merc. more than likely you have a "high-pressure" water pump, that will create pressures like below......<br /><br />"A couple of things to think about, 1) the temperature of the water that you are running in the hose is what compared to the lake water, 2) what kind of pressure are you running on the garden hose? (more than 14-16 psi. will open the poppet valve and all kinds of cool water will flow. Remember that your water pump will put out approximately 8-11 psi @ idle (800 rpm roughly) after the thermostats open up, before then 13-14 psi @ idle. Once motor is warmed up and thermo's open it will take approx. 2600-3000 rpm to develop 18-20 psi. If you have a pressure gauge you can see exactly when all this occurs. If you idle away from the dock (no wake area) say 200-300 yds. then gas it you would see the pressure gauge start to climb then drop back just slightly as the thermo's open then as the rpm's increase the pressure will start climbing again. Now at this point (around 2200-2400 rpm) if you can turn around (carefully) you should notice a good tell tale but you will probably not notice any water being dumped out the exhaust ports on the backside of the motor, and the pressure will be fairly constant @ around 13-14 psi. Keep increasing the rpm's, at some point around 2500-3000 rpm the poppet should open because there is enough pressure to unseat the valve. Once the valve opens turn around (carefully again) and now you should notice that along with the tell tale you also have water being dumped out the exhaust ports. As the rpm's keep increasing the gauge will keep climbing and finally stop around 22-25 psi.<br /><br />Remember calabrio, yours will be affected during idle and mid range rpms because your poppet valve is always open (dropping your pressure from 8-11 psi to only 2 at idle for instance)... If you fix that, I bet you will see exactly or close to what is above...<br />Ray2000 who posted above, doesn't have the same water pump as we do...He has a High volume water pump, so his pressure readings won't match what a high pressure pump creates.