Update and problem solved,went down to the boat today and started a search,checked the oil in both engines clean as a whip,started both and idled them at 700 turns let them warm up and checked temps on warm up with a heat sensing gun all normal both were in approx same temps as per gun on manifolds,then I took a hold of the water feed lines from the thermostat housing to the exhaust manifolds and squeezed them down almost cutting off flow and it felt like there was air passing thru as well as water,on the other engine I did not feel the same thing.I shut the boat down and locked out the starting system and removed the feed hose from the sherwood raw water pump and checked for obstructions it was clear, got a light down in the output side of the raw water pump to inspect the impeller and rotated the pump to see if the impeller had lost some vains for lack of a better word,all good.So i then removed the intake hose for the pump and looked all good layed the hose in the bilge and water poured freely from it,then I stuck my finger into the intake side of the pump and there was the issue,it was pretty close to plugged with what looks like old impeller rubber,since Iam new to this boat I have no idea when a pump was changed last but it appears as one had come apart and the pieces had dropped back into the intake hose and then came back partially blocking the pump intake and the pump was cavatating and this is why I could feel the hose surging,cleaned out the pump double checked the hoses and took it out ,perfect no steam and consistent water temps.Strange but true this is one for my books but she purrs along and Iam a happy man,hope this might help someone else in the future.Cheers