Overheating V.P. 2003

I have a Volvo Penta 2003 in my boat and it has recently put out less and less water from the exhaust, the pump is OK, heat exchanger clear etc....It has overheated twice and I am at a loss what is going on...any ideas?? I need to get it sorted and getting the motor out os going to be a SOB.
Cheers Iain

When you say "the pump is ok, heat exchanger clear etc" I assume you have replaced the pump impellar and also checked to see the fresh water intake isn't plugged. Is this correct.

John

Check exhaust elbow. Look where inlet waterpipe from heat exchanger goes into elbow for restriction. Common issue.

Thanks for input, I left the boat in Menorca due to the problem, going back in a couple of weeks. I willl check the discharge from exchanger to exhaust, I didn't think of that and someone else said it should be checked every 4 years or so. The pump is putting out 6 litres/min so must be pressuring up due to restriction ...only place can be there. I removed the exchanger and rodded out the galleries although no real problem, it was new a few years ago. Raw water intake clear..bit frustrating that I can't look at it straight away.
Thanks again