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crow
03-18-2006, 09:37 AM
Can anyone tell me the proper water pressure reading I should be getting on my 2004 16 with the 5.0 V8 MPI Mercruiser? The gauge is reading approximately 7 psi at WOT, about 5 psi cruising at 4000 rpm, and less than 2 psi at idle. I'm not getting any engine alarms, but those numbers seem very low to me. Another 16 owner said he was told that the water pump impeller on these engines goes bad very quickly, which could cause low water pressure, and is a difficult fix in the confines of the 16's engine compartment. Any thoughts?

Barry Eller
03-18-2006, 09:44 AM
The waterpump impeller that goes bad often is in the outdrive. The engine mounted recurculatiing pump on the engine doesn't go out much. Unless you have a belt driven seawater pump, I'm sure the impeller that you are refering to is in the outdrive.

I live in Gulf Breeze, where to you run your boat?

crow
03-18-2006, 10:14 AM
Barry -- Thanks for the clarification. What about those numbers...do they seem indicative of that problem?

I'm new to the area, but I've been putting in on the Blackwater and running the Blackwater and East Bays. I've ventured into the P'cola Bay, but 2-3 foot chop got to be a bit much for the 16. Where do you run?

Barry Eller
03-18-2006, 10:35 AM
I run in the bay and the sound, sometimes over by quietwater beach. There are a gew good resturants and watering holes that are accessable by boat.

I don't have a waterpressure gauge on my boat. Call any merc dealer, ask to speak with a service advisor, they can tell you the proper pressure. I don't think the pressure will be much higher than you are showing, you should be ok unless pressure falls to 1 or 2 lbs.

PM me sometime, there several Donzi's in the area. We will have a Donzi gathering soon.

boatnut
03-18-2006, 10:39 AM
This thread is educational to me as I have never monitored cooling water pressure in a raw water cooled boat engine. Where and how are you monitoring the water pressure? I think the key parameter in cooling water is flow (gallons per minute or ?) not pressure. If the cooling water path is not obstructed in anyway, I would think the pressure is never too high ---you have two big pressure relief leaks (the water going out thru the exhaust). Have others monitored this pressure? Ed

gcarter
03-18-2006, 12:41 PM
I'm running a Stainless Marine transom water pickup. I think there should be some pitot pressure at speed. I have purchased a Gaffrig water pressure gauge (that I'm looking for a place to mount) and sending unit that will be mounted at the sea water strainer. I'm only interested in observing pitot pressure. It would be interesting to know if the Johnson crank mounted seawater pump is being "supercharged".

Pismo
03-18-2006, 12:43 PM
Is it overheating or is the temp changing a lot based on how hard you drive it? If not then don't worry about the pressure. It is a low pressure, high flow system anyhow. The impeller is in the drive and is a fairly easy change if needed.

crow
03-18-2006, 02:11 PM
I'm monitoring the water pressure with the Gaffrig gauge installed at manufacturer. Other than that, I admit that I don't know much else about the water pressure monitoring system and the manual isn't any help.

The water temp is stable and does not seem to change drastically. Performance doesn't seem affected (other than needing a beginning of the year tune-up).

Thanks for the comments. Any others are still appreciated.

MOP
03-18-2006, 02:57 PM
I think you gauge is whacked "If all else is OK" an I/O will pin a 30psi gauge at about 3500 and idle at 8-10psi . This summer I swithed fro a BH drive to a BravoX with dual water pick ups, If I did much WOT water would force its way out of my strainer cap.
Big Griz posted on the water pressure at speed, it almost a shock at how high it goes at speed over 100psi at 80mph. I was a marine tech for many years and did a ton of running all kinds of stuff with the hatches open or off, you can actually see the circ hose between the pump and Tstat housing expand at WOT freaked me out at first.

Phil