Water Pressure

Ian

After some more checking, I have determined port side is working well with 1.5 PSI at idle and around 9 when taken up to 2400 or so, starboard always shows zero. I have come to the conclusion that the sensor is faulty, replacement on the way. Removing the connector confirmed the detection side is correct as it 2 beeped and VVM told me block pressure sensor was out.

However I have come to learn that there is not really an alarm on this sensor as the idle pressure is so low and the tolerances in the sensor don't make it viable as it would create false alarms per our buddy Wally at Merc. Explains why I don't see any with that 0 reading on starboard side.

Learning more every day, as we all do.

LaRea

Wait, are you saying that Merc disabled the "Sea Pump PSI Lo" alarm because the sensor can't detect it reliably?  

kordo

Wow, please say that that isn't true.  Can't believe that Merc would do that.

Ian

That's what it seems to be as my starboard is at 0 with no alarms so I asked more questions and got the following. To quote directly "As I understand it, we can’t do an alarm on water pressure (flow) because it is so low at idle (was 0.5 psi on my 350 MPI) and we do not want to put a map in the ECU for pressure versus RPM, mainly due to fluctuations in sensor accuracy you would get false alarms."
and "Coolant temp is a separate alarm and definitely gives you a fault (and can even limit engine power based on how severe the overheat is – engine guardian)."

Liberty44140

Following this closely as my dock neighbor continues to have an alarm on his 2004 merc 6.2 which he is told is a water pressure alarm. No overheat, has replaced sensors, can’t figure out alarm. Has had different mechanics on board. Would be crazy to find out there is no alarm. 

Ian

Unless that engine and ECU is different. Just by adding VVM showed me the 2 sensors and one at 0 and my concern there was no alarms prompted inquiries and responses.

kordo

Found the reason for the low water pressure.  Twisted raw water intake hose in bravo 3 stern drive.  Having it replaced this winter.

rasbury

How would that get twisted like that? You must have raw water pickup or would have toasted the pump and overheated?

Dream_Inn

Nice find @kordo !  & thanks for updating us with a great picture!  

Just to add, I changed my other pump to a Hardin this year and still have the slight difference in pressure (which I thought was due to the different pumps).  

kordo

No raw water pickup, just the water from the stern drive.  I had enough water to keep the engine from overheating, plus I ran it for most of the season at less than planning speed.  Even at planning speed (no more than 15 minutes at a time), the engine never overheated.  No idea how it got twisted, must have been when transom seal was replaced.

Black_Diamond

Been there on that twisted hose. The new replacement has that upper part hard plastic so it will not twist. It can twist when installing the internal hose lock part incorrectly. 

GMSLITHO

Had that once on my Alfa drive temperature would clim if the drive was all the way down a little trim and the temperature would drop