155 IMT

Hi

UK based so really need your help as rare engine here 

QSB 5.9 2012 200 hours

Take her out for first time at 75% throttle 22 kts 175f coolant both engines 

2800 rpm no issue sitting on plane. Vesselview 155 IMT – throttled back 10 times but repeated. Port 10-20 degrees hotter 

Engineer suggested wastegate may be stuck / corroded as boat been on unused for 12 months and on river for next 12 months @ max 5 kts 

This is what we were told we should be able to see move which I assume is the part they would fully.open to allow coolantto run freely?

Having looked at Tony’s tips it seems more likely dirty aftercooler requiring ultrasonic clean

I know almost nothing about engines but any advice would be gratefully received. Visually we could see no movement in wastegate but weren’t really sure what we should be looking for because out of view on starboard engine and we were caught drifting in a busy estuary with cargo ships.