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Mechanic says water in exhaust manifold

J

jjdiver

New member
"Hello, new here. Have been re

"Hello, new here. Have been reading through the current and archived pages.

Have a 85 (aprox) Sunrunner 23 with a Volvo repowered last winter with a 5.7Gsi of aprox 1994 vintage, retained the lower unit. Previously had a AQ285 and AQ225. I don't have the current A numbers on the 5.7.

Was in the San Juans (Washington for a week.) Return trip was to be about 60-90 minutes, so I loaded passengers and luggage, ran to nearby marina (about 10-15 minutes, parked in slip and had lunch. Moved from slip to fuel dock, fueled and added aprox one quart oil. Took about five minutes to escape no wake zone, took boat on plane, ran for five to ten minutes and loud knocking started. Wondered if I had hit something, shut down engine and raised lower unit. Couldn't see any damage. Lowered outdrive and started. Knocking/thudding continued whether in neutral or idling forward.

Idled at three to five knots back to slip. Had boat towed home (four hour tow.)

Mechanic says he found evidence of water in exhaust manifold, especially in cylinder eight (Dad's boat, some second hand information.) Mechanic thought boat was overloaded, but Dad and I said didn't seem that way, especially since we had pictures, swim step wasn't under water when loaded, luggage in bow, etc..

Has fresh water cooling except in exhaust manifolds.

Mechanic then asked if engine started normally, wondered if water was taken into exhaust during, or after fueling. Engine started normally, so that would seem to refute that idea.

From reading the forums here, it would seem the water in manifold is a problem. I joked with Dad and suggested we install mufflers out of the engine compartment going up a few feet (just a joke.)

I e-mailed Dad the link to a paper on resonance causing water to migrate up the exhaust manifold. He wondered if the manifolds had "lips" to prevent that.

I did have a five adults, two skinny teens and one very skinny twelve year old on board. Three of the adults are a bit large.

I am prepared to pay for all or a significant portion of the repair costs, if the dealer holds onto the water in the exhaust theory. I don't know what exactly Dad has for a warranty on the new engine.

Anyone have any comments, ideas or suggestions on the situation? I would appreciate any thoughts.

Thanks,

Jeff"
 
"Mechanic just reported that a

"Mechanic just reported that a rocker arm stud was broken (believe he said broken), pressed in a new stud and waiting for gaskets.

He says it was hydrolock. Not sure what I did that could have caused hydro lock. I don't understand why it idled out of the harbor for aprox five minutes, and on plane for another five minutes before the problem appeared. How can hydro lock occur when boat is on plane?

Jeff"
 
"hi am new around here had a f

"hi am new around here had a few boats in the past, but not apetrol one and one's that plane,
may be a silly thing to ask but what is a hydro lock?

tony."
 
"Jeff, I think that if the roc

"Jeff, I think that if the rocker arm stud was broken that could cause the exhaust to open or close at the wrong time and travel less than it should. If the exhaust valve is not completely closed during the intake stroke, water will sucked into the cylinder via the exhaust manifold and exhaust valve. That water will remain inside the cylinder during the compression stroke and since the water is not compressible it will "hydro lock" the cylinder. That can lead to damage like blown head gasket or bent rods or damaged crankshaft.

Perhaps the amount of pulses at idle or at low RPM was not enough to suck water into the cylinder via an incompletely closed exhaust valve, but that changed with higher RPM."
 
"I agree with El P.
I'd

"I agree with El P.
I'd also suggest that no work be performed until all is properly documented, or if the engine supplier approves, if there is a risk of voiding any warrantee!

I had this happen to me several years ago. (owner did not meet WOT RPM spec.... he damaged the engine..... took engine apart via another shop.... not cool nor fair!)

It is very unlikely that anyone would be willing to make good on a warrantee if they are not afforded the FIRST chance to evaluate themselves.... including where timing is set!


Just my two cents on that."
 
"I have seen this on automotiv

"I have seen this on automotive heads. Generally from over revving. And of course no hydrolock.....And I have seen general flaws in manufacturing cause this too after years of operation.
If man builds it, it will break. I agree with El P as well.
That's my two cents......"
 
"Mechanic states broken rocker

"Mechanic states broken rocker arm stud, bent exhaust valve and bent push rod at cylinder #8.

Surveyor the mechanic called in also found piston in cylinder number eight wasn't rising as high as other pistons, so there is probably a bent piston rod as well. Wonder why the mechanic (I should be saying company/marina) didn't find that.

Work is being performed by company who installed engine.

El Pescador---when and/or how did the water get into the cylinder?

So much fun. I hadn't hear the true mean for BOAT. I had previously understood that a BOAT was just a hole in the water you poured money into.

Jeff"
 
"El Pescador,

Great paper y

"El Pescador,

Great paper you linked too. I had read the paper, but wasn't sure you were suggesting the method in the paper or some other method. I would have to agree the paper outlines the method of water ingress that seems most likley to me. The mechanic is still holding to the idea that I overloaded the boat, which caused the water in the cylinder and resulting hydrolock.

Now I wonder if we are doomed to this scenario (vibration/resonance) repeating itself in the future, and if there is any way to prevent this from happening again? Time to reread the paper.

Thanks for your response, El Pescador and everyone else as well.

Fair winds,

Jeff"
 
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