hello, i have sunseeker 29 with twin 454 mercruiser. yesterday one of the elbow pieces , coming out of the exhaust manifold, "blew up, hole of 4 by 6 cm) also temp of engine went up , checked waterpump , that is ok, strange thing is that only one side of the exhaust heats up this much. today i replaced the broken piece, and started the engine, after two minutes one side heats up , the other stays fairly cool, please help.............

You may have a restriction in the manifold. Could be pluged with sand or salt (if you boat in saltwater).

Would definetly check for restrictions. Manifold gaskets are still cheaper than a new engine

I did not take of manifold, but if engine is started and you unscrew the bolt on the side of manifold, it sprays water at very high pressure., so i suspect there is no obstruction in manifold...

All that tells you is water is getting to the manifold. If you have wet riser joints the water has to get through those small channels at the riser. Get the manifold off and check it out. Just my thought, if somone else has a better way to check it for manifold restriction on the boat that would be good information.