Water pressure

I've just installed a water pressure gauge on a 1984 Mercury 60 HP 3 cyclinder, and tomorrow a new impeller goes in. Does anyone know what the normal water pressure should be at idle, and at WOT? With the current impeller I have about 2 psi at idle and not much more up to around 2000 RPM. Having no problems with the engine, just being cautious.

Re: Water pressure

Is this water pressure when in the water running, or on a flusher? Definitely Very Low for in-the-water pressure and you should see a drastic improvement after the new impeller is installed.<br /><br />Typically it's nice to see at least 5 psi at idle but it's extremely variable from motor-to-motor.<br /><br />10 psi running at speed is not unusual and hopefully you'll get more but again it depends on the design of the motor, the backpressure in the cooling system, the size of the impeller, etc.<br /><br />Most older motors would use a 0-15 psig gage so judge accordingly.<br /><br />The small-cubic-inch Merc 3's are very touchy about adequate cooling so be sure there's no other issues once you replace the impeller. These motors like to crack blocks if they're overheated so definitely stay on top of the cooling system!<br /><br />BTW make sure the lines for your water pressure gage are not clogged, as that'll skew your pressure readings too.<br /><br />HTH and Happy Boating.........ed

Re: Water pressure

Thanks Ed MC.<br /><br />The pressure is with flushing ears. Haven't had it in the water yet since the gauge was installed, and won't until the new impeller is installed.

Re: Water pressure

I had a 1980 50hp that at idle, pumped at around 2psi and peaked at 6psi at WOT.<br />This is about right for the 50 and most lkely the 60. A tired impeller<br />will not necessarily show signs of pressure decrease, but may just de-laminate<br />from it's bush and fail immediately.<br />Ed knows his stuff, and has helped me in my early Merc days. You're in good hands

Re: Water pressure

Were those pressures in the water or with flushing ears?

Re: Water pressure

That is per the manual and in the water. Never rev the motor over 1200 on muffs. You may not even get a reading on muffs, as there is a lot of leakage.