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Water in cylinders

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Water in cylinders

Postby billymac86 » Tue Mar 12, 2019 10:31 am

Completely baffled....I have a 19' 2004 Northwest Jet powered by a 5.7 Marine Power Vortec with an Xtream jet.
Just recently, twice now, it has come to a complete stop while idling after initial start up and getting up to operating temp 150deg.
Motor locks up, will not turn over....pull plugs out and she pumps out clear water(not coolant)...Dry out motor and she refires and runs fine.
After dry out, have done several high speed runs, everything OK.
Here's what I have done to this point.
Pulled the risers off, cleaned and dye checked for cracks, nothing....there's no gasket between the riser an manifold, sealed with gasket silicone.
Installed a new water pump, just because I didn't like the sounds coming from the old one.
Pulled and replaced the fuel/water filter separator...no sign of water in the fuel.
A little about me, I have been racing boats since the early 60's (outboards) and have dried out hundreds of motors...so very familiar with that routine.
Boat is kept covered during weather. Nothing after market has been done to the Marine Power unit since it came from the factory.
Sunday after the second lock up and dry out I kept it running at idle for over an hour and no problem...
I am absolutely baffled...hopefully someone can shed some light....thanks, Bill
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Re: Water in cylinders

Postby riverboater » Tue Mar 12, 2019 6:11 pm

Had a similar issue with mp engine,turned out to be air lock in manifold that caused the riser gasket to fail prematurely. Found carbon fiber gasket and ran bypass line from manifold to riser. Solved.
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Re: Water in cylinders

Postby Califbill » Tue Mar 12, 2019 8:50 pm

Bad exhaust flappers?
1991 21' Jetcraft Bluewater. T-8, 350 mpi
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Re: Water in cylinders

Postby Toddco » Wed Mar 13, 2019 7:07 am

X2 on the bad exhaust flappers. Once it is hydrauliced, do you only have to pull the bottom plug on each side? This is usually the case when flappers are not working correctly.
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Re: Water in cylinders

Postby gordo » Wed Mar 13, 2019 9:23 am

Is the idle extremely low? I've never heard of water pushing in thru flappers with the engine running. I've had my boat hydraulic thru the flappers, but only while not under power. [big waves pushed in on lake Ontario]. I installed metal flappers, like on top of a diesel truck exhaust, and counterweighted them to keep them shut with engine off. It's worked well, so far. Gordo
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Re: Water in cylinders

Postby Califbill » Wed Mar 13, 2019 10:27 pm

If the exhaust is low rise to the water and low idle and much cam overlap, may suck in water.
1991 21' Jetcraft Bluewater. T-8, 350 mpi
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Re: Water in cylinders

Postby billymac86 » Thu Mar 14, 2019 9:20 am

Thanks for all the comments.
Tuesday when I pulled the right side riser, I heard water draining as I loosened the upper hose clamps. I thought that strange since I thought the risers were designed to drain once the motor is shut off.
Note, this design MP exhaust system, the riser and exhaust manifold never share the same water...riser cooled with lake water as it exits the boat, manifold cooled with coolant.
Checked the weep/drain hole on the bottom of the riser, it appeared clogged...so cleaned out and re-drilled a little oversize.
This model of NW Jet was not equipped with flappers...there is a welded aluminum bottomless box on the transom that I guess is designed to do the job of flappers.
May have to look into a retrofit....
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Re: Water in cylinders

Postby lovetheedge » Thu Mar 14, 2019 9:41 am

You might contact marine power tech support, in years past they were very helpful. I have not used them in 4+ years. (877)-388-9555
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Re: Water in cylinders

Postby viking » Thu Mar 14, 2019 10:46 am

Many boats have boxes rather than flappers, so something else is the culprit, given that the problem apparently occurs while idling. How long have you owned the boat, and have you idled the boat for extended periods previously? Does the problem appear on both sides? Upload photos of riser setup. As per Califbill, water may "walk up" the riser if there's excessive valve overlap. That is, by design the intake and exhaust valves are open simultaneously during the "overlap", so the exhaust flow can reverse momentarily and some sort of harmonic will pull water up the tail pipe. (I don't know exactly the mechanism.) Overlap can increase if your valves are sticking significantly.
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Re: Water in cylinders

Postby billymac86 » Thu Mar 14, 2019 11:10 am

I have owned the boat for 4 yrs now. These last two times were the first times ever it has happened.
The first time, when drying out, it pumped clear lake water out the right bank only...the second time it pumped water out both banks.
Yes, it occurred while idling following initial start up. On the second occurrence I dried the motor out on the lake and then it idled without issue for at least 2 hrs.
I like the sticking valve theory since I had the motor serviced in January including an oil change, and I don't know what weight oil was put in.
And the only time it occurred was first outing following that oil change!!!
Sorry, I don't know how to post a .jpg file to this board...I do have several pics of the manifold riser system.

ps.....I have had many email conversations with MP tech, and they have been extremely helpful...but never mentioned valve sticking...
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Re: Water in cylinders

Postby Buck Master » Fri Mar 15, 2019 12:18 am

I had a similar issue but the water never made it into the cylinders. It would leak out the manifolds where they met the block. It was a timing issue. Apparently, there is something possibly in the distributor that controls this. Maybe it was springs. Can’t remember exactly. Only happened at idle as timing changed when I throttled up.
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