'99 Ski GT40, reduced water flow and port side overheating

[jhersey29]

All sounds good to me. The only distribution block is the thermostat housing.
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[jhersey29]

On my 99 potentials for air leak would be. Connection at hull, t-connector for the hose hook up, hose connector plug missing rubber washer, raw water filter connectors, crack in raw water filter cup, rubber washer missing from raw water filter cup, transmission cooler connections, lines feeding water to the transmission, internal leak in the transmission, raw water impeller connection, raw water pump, then your at the thermostat upper housing that feeds both exhaust manifolds and circulating pump. Don't crack your upper housing they don't make them anymore due to a tooling issue. Of course all the hoses along the way.
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[Skidave]

Wow, from your video, that is really reduced. I would check the output of the hoses like I said. Best case is there is some occlusion at the 90' brass fitting. Seeing the waterflow from the hoses will tell you if it is before the manifold / riser combo or not related to the manifold / riser.

[nate800]

The distribution block was pulled last night. There is some scaling and buildup, but nothing that would be causing a blockage. I will be removing the hoses from the manifolds and firing the boat up this afternoon to see how the water flows. Even if I find that my manifold was blocked, that doesn't solve my overheating issue. The port bank is still not cooling properly.

In the video I posted, I am running the boat on a hose at 30psi. That's far more pressure than the RWP would generate, and I'm still having a flow issue.

[SilentSeven]

30 PSI of water forced into the raw water pump would seem to mitigate any supply issues. Trust you had sufficient volume with the pressure to meet the draw from the pump....

Can you tell from the distribution block if water MUST go through the engine before it flows to the exhaust manifolds? From the diagram I posted, its not clear. It would seem to me there must be a path where the raw water has a path direct to the exhaust and can flow around the engine. This would be required to allow the thermostat to close and recirculate the engine block water so it heats while the raw water pump flows cold water to the exhaust.

Assuming the above is true, hard for me to visualize why a 30psi hose wouldn't flow water to each exhaust equally. Any possible explanation here?

Regarding the hot cylinder head....thinking out loud...maybe its not a water supply issue..maybe it's a head gasket failure andyou are getting cylinder pressure into the cooling system. That might divert water away from the cooling passages and cause that head to overheat. In car with a pressurized, contained water system, this is easier to check. Not sure how you can check on the boat except maybe feel for pressure in the manifold supplies hoses. Also not sure that explains the lack of water to one side.

[jhersey29]

See this.picture. http://www.nautiqueparts.com/housing...ostatford.aspx . The top right tube is the input from the raw water pump. The 2 other tubes feed directly to each exhaust manifold. The large hole is where the thermostat is located. The port side is actually the single outlet.
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[jhersey29]

Another thought. Do you have the rubber o-ring in the impeller housing and the paper thin gasket in the impeller housing? Maybe sucking air in that area.
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[nate800]

Alright folks, update:

Removed t-stat housing (as jhersey29 showed) and it is clear. Not the cleanest thing in the world, but certainly not blocked as the video I posted would suggest. Here is a photo with one hose removed: i.imgur.com/1hEdOEj.jpg

You can see right through the T to the other manifold hose. No problems there apparently.

However, when running the boat today I had the same problem shown in the other video. Nearly ZERO water flow from my port side hose, even with the manifold disconnected. Just a trickle, while water dumped out of the other hose. See video here: https://www.youtube.com/watch?v=C0XF...ob1nkA&index=2

When backing the boat into the river to do a flow test solely running the RWP, we have noticed a very small vacuum kind of sound right at the connection of the hose to the thru-hull water intake. It only happened after shutting the boat down, just a verrrryy slight sucking sound. Is this of potential concern? I don't think that this would be causing the major flow problem, especially since the problem is persisting once the thru-hull connection is bypassed via garden hose.

[SilentSeven]

What a puzzle. Does PCM have a tech line? Maybe it's time to try call them for some guidance? Or maybe Skidim?

Short of this, I think you keep crawling through it one part at a time. I'd pull the engine water pump next and inspect the points where it connects to the engine and the pump itself.

A leak in the intake line could lead to air, reducing the water volume but I would agree that your hose feed suggests that not the root issue. However, I'd fix any leaks I found.

[nate800]

I found a point the port side of the engine that apparently is prone to blockages. I believe it filters water before it goes into the tranny cooler? Either way, I found that this part can cause circulation issues so I'm going to pull it tomorrow and have a look.

[jhersey29]

Does your upper thermostat housing have 25002 stamped in it? The starboard side should not be straight. It is normally bent downward and backwards at an slight angle. The port side is straight. I have one I replaced in front of me and you can not see all the way through it due to the bend in the starboard side. Also is your thermostat suck open? Maybe most of you water is getting sucked into the motor by the circulating pump. Does you engine temp gauge go to 163 then down to about 155. It should repeat this cycle a bit and hover around 160. If it's not getting to 163 then I bet your thermostat is stuck open.

[nate800]

You are correct, my thermostat housing is not straight. I shined a light through it and ran water through it.

The thermostat is functioning properly. The videos I posted are of the motor after it has reached operating temp and the thermostat is open.

[DanielC]

If I am not mistaken, the raw water pump should pump way more water than is necessary to keep the engine cool. This is so the excess water not needed for engine cooling is bypassed around the engine, and is dumped out the exhaust manifolds, to cool the exhaust system.
When the engine is cold, and warming up. the water in the block is just circulated by the circulating water pump, and is held in the engine block by the thermostat. The raw water pump just keeps a slight pressure on the engine block, and dumps excess water out the exhaust. When the engine gets warm enought to open the thermostat, warm engine water is dumped out the exhaust manifolds, and cool lake water replaces the warm water in the engine.
In other words, I do not think the total volume of water coming out the exhaust should change much when the thermostat opens.

[Skidave]

For what it is worth, I would call Discount Inboard Marine and run this past them. They might have had some similar customer issues like this and have some knowledge.

[jasper]

Taking some of what SilentSeven said, "wondering if you have a problem with pulling sufficient water from the lake," and DanielC said, "the raw water pump should pump way more water than is necessary to keep the engine cool," and looking at your video, I think the total water being pumped is inadequate and thus most of it is going to one side (though I must admit, I don't know why). But simple things first. Your impeller is not new but looks fine visually, but if you are not pumping enough water, sometimes the hub of the impeller will spin inside the rubber wheel with the vanes. If the impeller is beginning to do this in a sporadic fashion, it could reduce the water flow. It is worth a check (new impeller install?). The question I have is if reduced water flow would cause water to favor one side over the other. That I don't know. But I do know that some people have had impeller hubs spin in the impeller and thus not pump. I'm speculating you are at the beginning stage of this very problem. If so, it would be a simple fix.