Mercury Outboard Pumping Steam

I have a 2000 model 150 Saltwater Mercury outboard that is pumping steam/water out the tale-tale at any RPM above idle. Started while going out to sea and noticed steam rolling up behind engine while running. Alarm did not go off. Let engine cool, restarted and had a strong stream of water, but with RPM increase, started pumping steam/water. Was towed and have replaced thermostats, pressure/poppet assembly, impeller, added temp gauge and flushed engine. Changes made no difference. At idle with ears installed, temp is running 175-180 and with slight RPM increase, goes to 200 plus and starts spraying steam/water from tale-tale. Engine seems to run normal, but not sure of unseen overheat damage. Added oil to gas plus injector to heal possible problems. Any help would be appreciated.

Re: Mercury Outboard Pumping Steam

not familar with the engine but to me the symtoms, sound like on old blown head gasket or such, compression/exhaust getting to the cooling system.

Re: Mercury Outboard Pumping Steam

Head gasket would be my best guess. The have a metal ring around the piston hole and for some reaso they do like to rust away. Maybe you have caught it before any damage was done. I either do or have mine done about every 3rd year as I do all my running in salt water.