Volvo MD7B making lots of white smoke after idling for 15 minutes and blowing oil out the filler cap

My Volvo MD7B has been running great. The last time I started it up to exercise the engine, I let it idle for about 15 minutes and was planning to put it in gear and run it under a load for a while, which is my normal practice. I usually do this every couple of weeks if I haven't taken the boat out. All of a sudden, while still at idle, it started blowing a lot of white smoke out the exhaust. The engine temporarily slowed down, then sped up. I immediately shut it down. It was pumping water good and the engine temperature was fine. When I inspected the engine, I found oil on the valve cover. I cleaned it up and started it up again and went down below to see where the oil was coming from. I didn't see any oil coming out at low idle. I increased the rpms and oil started coming out of the oil filler cap and it made tons of white smoke again. I shut it down. I didn't hear any knocking or other unusual noises.

This sounds like blowby. But does the large volume of white smoke, and I mean a very large amount of white smoke, mean water in the compression chamber? Could this be a blown head gasket? Is there any trouble shooting I can do before pulling the head? What do look for when I pull the head?

Thanks for your help.

Is the crankcase breather blocked? A little funny to suddenly get lots of blowby. White smoke most often means water as you note, but excess fuel in volume can also give whitish smoke. So crankcase breather, injectors, compression test are possible pre-teardownchecks. Most likely a head gasket though from what you describe. Water in cylinder making excess compression, so blowby and white smoke. I wouldn't try to run it again in case it hydrolocks and I wouldn't leave it for too long if there is a chance that you have salt water in a cylinder.

I've tried to reply twice and it doesn't accept it for some reason. I was logged in both times.

I hope this post goes through.

I pulled the head and found water and diesel all over it. I drained the crankcase and it had a lot of water in it..SALT WATER!!! So I flushed the crankcase with fresh oil and turned the crank a few times to wash it off. Does anyone know of a good method to get all of the salt out of the crankcase? I was thinking about filling it up with Marvel Mystery Oil and rotating the crank to try to wash it all off, but I'm just guessing.

I haven't taken the head to a machinist yet, but it must be warped. The head gasket was intact. There were some subtle signs of leakage next to the exhaust manifold, but no smoking guns.

All input is appreciated.