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

[nate800]

I've been plagued by a port-side engine overheating issue for the past few weeks. I pulled my exhaust off this weekend and found that I have greatly reduced water flow from the port side. I was running the pipes into 3-gallon buckets. When the starboard bucket was full, the port bucket only had 2" of water in it. You could hear the port cylinder bank start to run rough as it overheated and the manifold became very hot. Obviously, something isn't allowing water to flow properly.

My RWP, t-stat, circulating pump, and hoses are all fine. I hooked up a hose to the manifold inlet and flushed it, water flow through it seemed to be good. I also removed the riser, flushed it separately just in case, and replaced the gasket.

What should my next step be? Could I have a blockage somewhere between the manifold and engine block? I'm planning on removing the manifold today.

[jhersey29]

The.thermostat has 3 outlets. Large one to the thermostat, two small one the each go directly to exhaust manifolds/risers. Clean out the feeds to the exhaust manifolds from the tstat housing. Most of the water will flow through those ports when the tstat is open water will flow in all 3 directions. To circulating pump, both exhaust manifolds. that little water out one side seems like it should be the tstat housing or blacking in the hose to the port exhaust manifold. I cleaned mine out with a small sanding cylinder foe my dremel.
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[nate800]

I have checked these outlets, the hoses and tstat outlets are clear.

[SilentSeven]

You may wish to pull off the manifold riser and look for blockages and scaling in the pathways. Simplest starting point.

Be sure to have a new gasket on hand; you may need new bolts as well (got mine at the local Ace HW for much less than what the parts places wanted)

[nate800]

I have had the riser off and found no problem! I installed a new gasket and put the riser back on. I was planning to remove the entire manifold today to inspect it for blockages or signs as to the main problem, but work is getting the way (**** jobs, who needs them anyway!). I'll be popping the manifold off tomorrow. I'm not entirely sure what I should be checking for though.

[SilentSeven]

I'm almost wondering if you have a problem with pulling sufficient water from the lake?

Unless you have a lot of scale in the engine or bits blocking the water flow (and it sounds like spot checks for that are coming up negative), the only other think I can think of is insufficient supply to get water to every part of the motor.

If you haven't done it, might be worth pulling the supply hose from the water pump and blowing backwards to the water pickup to see if it's partially blocked or not.

[nate800]

It doesn't appear that there is an issue pulling water. I disconnected the intake hose from the thru-hull intake and clamped my garden hose directly to it. No blockage in the hose. When running the engine on the hose like this, there is still very, very little water coming from the port exhaust pipe. I pulled the manifold today and flushed it with no problem. I pulled the thermostat housing where the water exits the block and found some scaling.

How could this be causing such a dramatic difference in water volume? The water goes in the starboard and port inlets via circulating pump and then comes out the top and hits the thermostat T and exits via manifold. Tstat passages and hoses to manifolds are all clear. I'm really stuck here.

[Skidave]

Nate,

I'm just down the road in York. Time is limited, but if you need another set of eyes, let me know. Are you running this at idle speeds when connected to the hose? I would not run it much more than idle or short small bursts of increased rpm. Is your impeller new in your raw water pickup-just to make sure? When you are testing with the engine running, have you looked at the flow of water coming out of the hoses that feed the manifolds (from the T-stat)? It sounds like you are checking after the water flows through the manifold. Please clarify. You may want to just wait to the motor cools down and drain the entire system. I doubt you have something stuck in a passage, but it can't hurt at this point. Send me a PM if you want my cell number.

Dave

[SilentSeven]

Really odd one. So, it sounds like this then....all this is true?

• You have no blockages in the water pickup limiting water volume
• When you pressurize the pickup line with a hose feed, you are still seeing flow issues exiting the manifold
• Your impeller is OK and belt is tight
• The water lines feeding the exhaust manifold are not blocked
• Water flow to the one manifold is less than the other
• You don't have a blockage in the exhaust manifold itself

If all this is true, then really it seems like there is not much left except some internal blockage the motor itself.

I might try to free things up by connecting the hose to the manifold feed line and running pressurized water 'backwards' through the engine. I would open up the water drains / heater lines etc selectively to try to change water flows and pressures to 'knock loose' any stuff in the block. I'd also try to 'surge' the pressure in block by changing the hose pressure as well.

If this can't sort it out and no one has any other ideas, seems like the next step might be to pull the cylinder head on problematic side. Bummer.

[nate800]

Hi Dave,

Yes, only idle speeds when on the hose for under a minute at a time. No revving. The boat first experienced this issue a couple weeks ago, it was idled to the ramp and has since been started 3 times on a hose.

The impeller is not new, but I did check the impeller and RWP for damage. It is a-okay.

I have not started the motor with the hoses disconnected from the manifolds, that is actually my next plan of action. I pulled the manifold today and ran water from the inlet up through the riser, good flow.

How would I go about draining the system?

Here is a quick video I shot: https://www.youtube.com/watch?v=CMr2-EwIC_I

[nate800]

SilentSteve,

Yes, all of that is correct. Please check out the video I just left in a previous comment, the flow variance is significant.

I'm going to try backflushing tomorrow. I'm going to put the boat as close as I can to my highest-pressure spigot and use a very short hose for the best pressure. Worst case, I'll have to pull the port head.

Does anyone know where I could find a diagram showing the cooling passages through the engine?

[SilentSeven]

Interesting vid.

From the factory owners manual, here's the water flow diagram. The more I think about it the more think your problem is in the distribution section where I marked it.

[jhersey29]

Sure seems like more water should come out when the thermostat is closed than that. Did you check the 90 degree elbow in front of the exhaust manifold and double check that thermostat housing. Hose is clear with no blisters from a prior overheat?
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[DanielC]

See this thread:
http://www.planetnautique.com/vb3/sh...ushing+adapter

You can use the adapter to pressurize the intake hoses to the raw water pump. This makes what is normally an air leak more evident.

I believe a GT-40 raw water pump should be able to pump 5 gallons of water, in 15 seconds, at 3000 engine RPM.

My first thought is your raw water pump is not pumping as much water as it should.

[SilentSeven]

If all this is true, then really it seems like there is not much left except some internal blockage the motor itself.

I would also rephrase this to say that I think the blockage is where the water enters / leaves the block -basically where the waterpump attaches. Or as posted above in diagram, in the distribution section.

I really like Daniels idea + pulling the distribution block.