So at this point, I have replaced the water outlet gasket, removed thermostat and flushed block for about 30 minutes. Took boat out 2 more times since, and no change to the low water pressure and higher water temp situation.

I hate to even ask, as I have been purposely avoiding this point. Could it be a blown head gasket causing the low water pressure and higher water temps?

I'm not making oil (at least not showing increase/water on dipstick).

I had planned on doing top ends this winter, but not sure I should wait that long - if, in fact, this is a head gasket issue.

My next step is to use some clear tubing to check for bubbles.

Thoughts?

If the head gasket was leaking, you would see it externally leaking into the bilge or would have a lot of steam in your exhaust.

I don't see it leaking in the bilge, but I can't say that it's not.

I do have a little steam, but lot's of boats do - so I've not thought much about it.

I picked up some clear hose, and will check for bubbles tonight hopefully.

Put clear hose between thermostat and header and have bubbles!

I guess time to start wrenching. Somebody tell me I'm wrong!

First part of video is at idle, last part is while running on plane. Difficult to see bubbles while on plane, but they were much more concentrated than idle.

http://youtu.be/46LrkmxAHWw

Looks like head gaskets are toast. Was planning to do top ends this winter, but looks like I can't wait that long.


From Cumberland thread....

Well, it's gotta be the source of overheating - but there is still a water pressure issue. I'm thinking about just going through hull with strainers, as the both wasn't rigged that way. That should eliminate any water delivery problems.

If you are going to do that, I would also run 20 psi or lower pressure blow off valves with by passes.

Good luck, make sure the builder inspects those blocks well for cross firing from 5 to 7 across the deck

Did you positively identify a blown head gasket? If not, do leak down tests! Nothing worse than getting it apart and NOT seeing what you thought you would.
The bubbles could be coming from an inlet leak, or just be water passage cavitation. Also, the hull was just in front of your PU creating bubbles.

I was planning on top end rebuild this winter anyway. Based on what I've read and conversations with Eddie Young, I'm lucky that I've gotten 260 hours out of the stock gaskets!

I pulled the heads off of my 575 at 100hrs and the gaskets looked like they were within minutes of failing, BUT they were torched between the cylinders. There were no integrity issues at all where the water passages were sealed. I am sure that you need to replace the gaskets, but I don't think it is causing your low water pressure issues. For a gasket to be leaking bad enough to cause low water pressure it would have to be dumping a tremendous amount of water either into the bilge or into the engine, which in turn would end up in the bilge once the crankcase filled. If that much water was leaking from the coolant passage into the cylinder and going out the exhaust, it would have most likely hydrolocked by now and done some damage to the piston or rod. I don't know what the answer to your low water pressure problem is, but I don't think head gaskets will solve the issue.
I am just across the river if you need any help. I have a fully equipped shop and can help if you need any assistance.