Beta 2203 overheating

[Gumpy]

I have a Beta 2203 in my boat and have at last got it off the canals and on to some deep water.
At 1500rpm / 5mph its fine and will go on all day at 80deg
At 2300rpm / 7mph and max revs the temp starts to climb after about 5 minutes.
It is over propped as it should rev to 2800 as it does out of gear.
It is heat exchanger cooled and not skin tank, so its not that the tank is to small.
I have checked the tube stack and there is no impeller bits in the end caps.
Impeller looks OK however there is a lot of scouring on the lid of the Jabsco pump which leads me to think that it might not be the correct impeller. As soon as I can get one,am out on the river at present, I will change it.

Now what have I missed? could the fact that its over propped cause the overheat?

Boat by the way is a 60ft narrowboat with a 19" prop that I think is 15" pitch (not measured just calculated from speed and engine revs)

 

[sailorman]

would suggest on the suction side.

 

[Gumpy]

would suggest on the suction side.

there is no loss of level in the strainer (which is clean) none of the pipes appear to collapse but I haven't checked the oil cooler tube stack which is between the strainer and the raw water pump.

 

[sailorman]

fuel not cooling

 

[Gumpy]

Im confused now
How can that cause the engine to overheat?

 

[Gumpy]

May have sussed it, got to go in water again tomorrow.
It looks like the pick up mesh may be partly blocked, cant see being done by feel.