Indmar LS3 manifold overheating
 

Ok my boat has always had the issue of trying to overheat when I first drop it in but once I give it a little gas it goes away and is gone for the day. I rode yesterday and on the way back to the dock I was running around 32mph and I noticed a burning smell. I stopped and popped the engine cover and my starboard manifold had bubbled the paint on it and started to melt the rubber coupling connecting it to the exhaust. We limped back to the dock and it never seemed to get very hot as long as I was going slow. After some research I've found out there was a service bulliten posted about the elbow and plumbing that sends water to the manifold to keep it cool. Sounds like it's the problem but my only concern is why now at 400 hours and not anytime before? The only changes I've made recently were changing my prop from a 2313 to a 2315. I bought the boat used so the warranty is gone so I'm trying to learn as much as possible.

Overheating when 1st put in could be caused by a worn impeller,