Low sea water psi at idle and overheating after running - merc 5.0 mpi bravo

[Marnold100]

I have an 04 sea ray 240 sd with a 5.0 mpi bravo 3 with the three point drain system.
Problem is after running I idle back to the dock and then I overheat. Water psi at idle shows 1.0-1.2 psi.
I replaced the impeller and the brass housing looked good- I.e. was not badly grooved. I do not see any leaks between the house from the lower unit to the sea water pump.

I just bought the boat. Everything functioned at time of purchase(so it seemed). boat was completely checked out by dealer 30 engine hours prior to my purchase. Boat was in salt water and dry rack stored after each use. Manifolds and risers are original. 484 hours on engine.

The water pump would not self prime after I completed my impeller install project. I had to increase the rpms to get water moving. So a leak or blockage somewhere. At the lower unit pickup or corrosion somewhere?

I am reading a thru hull water pickup has worked for others in this I boat forum. Thanks.

Engine serial number is OM668946

I now run it in fresh water.

 

[LagunaBlue]

Re: Low sea water psi at idle and overheating after running - merc 5.0 mpi bravo

The Bravo has the engine mounted sea water pump. Have you inspected it? I'm not exactly sure on what the flow rate for the Bravo is, however the test procedure is in fact in the service manual.

Was the motor flushed after each use by the previous owner? I would also pull your manifolds and risers and check for rust and/ or corrosion blockages. 484 hours and almost 10 years is a long time for manifolds & risers in a salt water application. I wouldn't doubt that there is corrosion inside the passages. Time to replace them most likely. Also check the thermostat & housing.

Report back after consulting the flow test in the manual & checking the manifolds & risers.


-Mark

 

[Marnold100]

Re: Low sea water psi at idle and overheating after running - merc 5.0 mpi bravo

The Bravo has the engine mounted sea water pump. Have you inspected it? I'm not exactly sure on what the flow rate for the Bravo is, however the test procedure is in fact in the service manual.

Was the motor flushed after each use by the previous owner? I would also pull your manifolds and risers and check for rust and/ or corrosion blockages. 484 hours and almost 10 years is a long time for manifolds & risers in a salt water application. I wouldn't doubt that there is corrosion inside the passages. Time to replace them most likely. Also check the thermostat & housing.

Report back after consulting the flow test in the manual & checking the manifolds & risers.


Thanks Mark. The motor was flushed, or so I am told, after each use since it was apart of the dry stack service.

Inspected the pump, it is in good shape (put in another new impeller since we had it apart). Had a mechanic from marine max look as well (side job). Thermostat is next. Still getting 1.1 PSI at idle.

Mechanic suspects corrosion in the lower unit if thermostat doesn't take care of it.

One thing to note; at idle, the temp slowly increased, but upon revving the engine, the temp quickly dropped leading mechanic to believe the thermostat is sticking since the drop in temp was so abrupt.

I know manifolds and risers are eventually in the equation. Mechanic took a look and listen and didn't see or hear anything to be concerned about yet.

I'll consult the flow test in the manual.