2003 496 high water pressure

[Tomco]

Went out on Saturday for the first outing of the year and when filling out my log, noticed that the water pressure on the port side (@1030rpm) was about 7psi and on the starboard side was 20psi. We turned around and headed back, on inspection saw nothing obvious why the starboard side would be nearly 3 times as high. From my log last year both engines ran at about 7psi (@1050rmp) and one of the mechanics confirmed that this was about the right pressure.

These are 496 mags, closed water cooling, with Bravo III drives and the raw water impellers were changed on both engines a year ago. When they pulled the boat last fall, the water pressure on both sides was fine ... first run this year, it would seem that something is plugged.

I have been looking at schematics but cannot determine if the sensor is before or after the water pump - I think it might be on the inlet side, just inside the transom ... but I'm not sure. If I can find them, i plan to switch the sensors to eliminate that possibility. If it is not a sensor, any ideas what might be causing the high water pressure and how to check/clear it?

Thanks,

 

[jason78]

My first guess would be a plugged or bad PSI sensor. Since you have twins, it is easy to swap the sensor and see if the problem follows the sensor or stays with the engine as it sounds like you have planned to do. This ~30 minutes could save you hours and $$ in troubleshooting if it does indeed end up being the sensor. Not sure if I would say it is a common problem but these sensors failing have certainly had their fair share of discussion here. On the small blocks the sensor is installed in the power steering cooler that is on the top rear of the engine. It is black and tublar in shape; maybe 1.25" or so in width. Looks like a mini heat exchanger. Not positive but I think the big block has it in the same place. Should be easy to access.

 

[Georgia SeaDawg]

My sensors are on the manifolds. Very easy to change. I would suggest purchasing and extra sensor or two and keep on board. These sensors do fail, and they always seem to fail at the worst time.

 

[Tomco]

I will be back on the boat this weekend and will track it down ... although I am not sure what I'm looking for. Any chance you have a picture and could point it out? Once I see it once, I'll be good to go.

 

[jason78]

My sensors are on the manifolds. Very easy to change. I would suggest purchasing and extra sensor or two and keep on board. These sensors do fail, and they always seem to fail at the worst time.

Are you by chance referring to are the Exhaust Manifold Water Temperature sensors? There is one of those on each side. The sensor he needs is the H2O pressure sensor.

 

[tbirdvet]

I had the exact same issue. It was a bad sensor and I had it replaced by the dealer (it was still under warranty). These go bad all the time I've been told.

 

[Tomco]

To provide an update. It turned out to be a bad sensor - the sensor is on the raw water pump in case anyone else is looking for it. I switched the sensors between the engines and the problem followed ... new one on order for this week.