looking at a boat in CA .engines in boat are 502 /30 over. one engine has been rebuilt . while driving the boat the engine that had the work done on it had a lot of steam comming out the exhaust .the other engine had none.the owner would not run the engine that had the work done on it over 3,500 rpm for break in reasons.both engines oil and water temps ran about the same.could this steam thing be a problem in the rebuilt engine

What kind of exhaust is on the boat? Manifolds/risers? Headers?

cmi cool collars