News on the engine front: After flushing the engine approx. ten times with 5% H2SO4, the cylinder head now looks like new. Also the sacrificial anodes are 50% gone. Heh. But the problem remains: when running the engine in idle mode the temperature is fine; when the engine has to move the boat, it will overheat after only three minutes. Ten minutes later we can already see a little steam coming from the exhaust.
Yesterday I again checked the impeller and replaced it (just in case) but that didn’t do anything. I also cleaned the seawater inlet and filters which means EVERY part of the cooling system now was checked.
My last hope is the following: I don’t think there’s enough water coming out of the exhaust. Maybe the whole system is flawed from the beginning and we just need a water pump with a higher throughput ? The manual says, it should pump 800l/h at 1400rpm which I will measure later. Any other ideas ? Anyone ?!?