Intermittent overheating on VP 5.0 GX-I

[veeru]

Raw Water intake engine with Duo Prop Drive (2008 Model)

Fighting with an intermittent overheating problem. Checked the boat on dry dock with the Water Muffs and nothing unusual but when on the high seas the STARBOARD side risers are running about 10 degrees hotter than Port side. Yesterday is ran hot for MOST of the time since start and needed a rest every 10 minutes for a 30 min trip. Engine has about 400 hours and the problem appeared recently.

We stripped the Outdrive lower water intakes and cleaned them completely.
Fitted a new impeller for raw water pump.
Removed the RAW WATER PUMP OUTLET hose to do a test with Engine running briefly and the water output pressure and volume is very good.
Exhaust Manifolds were replaced about 3 months ago and she has done less than 8 hours since then.
Checked all hoses and clamps and no sign of any air intake in the water anywhere.

Any comments will be appreciated

We were thinking of opening the blue drain plugs for draining the riser and heads from the water and flushing it.

Can the thermostat be faulty?? If so why would the Engine sun hotter on the starboard side and not port when tested with a laser gun.

Would anyone recommend disconnecting the inlet water pipe to the STARBOARD side Head and flushing that independently to see if there is any blockage there, or should we simply remove the thermostat housing and do a test w/o the thermostat. (Manual expressly forbids removing the thermostat and running the engine).

 

[Thalasso]

Starboard side will be warmer then the port.How much warmer i really don't know but they do. What does the gauge show? Any alarms?
How much diff. in temp between the two?
Edit:
I see you said 10 degrees. That's okay

 

[veeru]

Tks Thalasso. Starboard is 10 degrees to 15 degrees C higher than port (Are you saying it is normal). Yes when driven yesterday alarm came off after 8 minutes of use at 3500 rpm. Turned it off every 5 to 10 minutes to limp home from high seas.

If someone knows what is the standard expected temp on the 3 sensors ie 2 Exhaust risers and one on the thermostat housing, we can compare them with the Laser gun and rule out a faulty sensor. (Worst case scenario could be a leaking head gasket but its too far fetched as overheating comes and goes.)

We did the following today.

a. Put water muffs and let engine idle for 15 minutes. Gauge shows 175 deg F (Normal temp). Laser gun showed 60deg C for Starboard on Exhaust riser and 45 deg C on Port Exhaust riser with 65 deg C at the sensor on the thermostat housing.
b. Did the same at 1200 RPM for 5 mins Gauge showing 175 deg F (Normal Temp). Water was coming out of exhaust but not constantly. We tried the Blue connector water inlet inside the Engine room to provide fresh water and the water output from exhaust was more constant.
c) Opened the OUTLET pipe of the Impeller pump and saw water coming out with a decent pressure and volume at 600 RPM (So the assumption is that impeller is working fine)
d.) Refitted the above hose and removed the hose that GOES to the Starboard side head. Ran engine and saw water coming out of the thermostat housing outlet for this hose quite freely. .
e) Drained the cylinder with the blue tap open ans flushed it.
f. The Impeller housing drips ONE drop of water every 30 to 40 seconds.
g. Replacing the impeller and O ring now.

NO ALARMS when idling or running on dry dock.

Once in water and you go at about 3500 RPM temp goes up to 275 .with alarm on.

Can there be a case of a faulty sensor which leads to an overheat signal.

 

[Thalasso]

Start looking to see where it's sucking air. Most likely it will be at the raw water impeller. This will cause a overheat. Put a clear hose on and watch for bubbles. Go up to the stickies and click on Volvo Penta. Click on overheat and you will see what i am talking about