[Tiara Open] Exhaust manifold getting hot

[0007Boating]

Went down to the boat yesterday and here's what i did. I replaced the coolant hoses going to and from the exhaust manifold, no change. Then i swapped the oil coolers from one engine to the other, no change. I swapped the temp sensors, no change. I looked at the impella and that was fine. Last resort i swapped the temp gauges, no difference. I ruled out as much as i could without spending too much money but still nothing. I decided to take her out for a test run under a load instead of sitting at the dock. When i was running at 1000 rpm's the same engine was getting up to almost 200 deg. once i got out of the no wake zone i brought her up to cruising speed 3200 rpm's and the temp came down slightly to around 195 deg. I then opened her up for about 2-1/2 min toped out at 4600 rpm's and the temp came down to 180 deg. Came back through the no wake zone at 1000 rpm's and too my surprise the temp only came up to 185 deg. is it posable running her hard for a few min cleared something out of the cooling system? Im going out today with the family, keeping a stiff eye on the temps and i will post the results when i get back.