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post #1 of 12 Old 04-03-2017 Thread Starter
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Yanmar Hydrolock

Engine started a month ago, went out yesterday and encountered what I believe to be a hyrdolocked motor. I initially diagnosed it as weak batteries (a solid clunk/partial turn of the motor, just to fall back to starting position), but voltage was fine. After some quick research found that it might be hydrolocked and I just needed to vent the engine while starting. It took a bit, but opening the vent enabled the motor to turn and after long enough it caught and started.

So question time:
What causes hydrolocking and how do I prevent it? Other than a minor inconvenience that ruined a day of sailing, the motor currently seems fine.

Thanks!
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post #2 of 12 Old 04-03-2017
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Re: Yanmar Hydrolock

Hydrolocking is most often caused by cranking too long without the engine firing to blow the water out the exhaust.. the raw water fills the system to the point that water gets into the engine through an open exhaust valve. Could this have occurred?

Some boat are prone to backflooding the exhaust systems under certain angles of heel, usually in a particular tack.. another possibility?

Also, if the engine is deep in the boat there will be an antisyphon loop.. if this loop's vent has plugged you may have 'sucked' water through the RW through hull.

I hope you ran the motor for a while and let it get good and warmed up.. and I suggest you change the oil sooner rather than later. - and close the RW intake between runs until you sort it out.

What boat?
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1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)

Last edited by Faster; 04-03-2017 at 12:45 AM.
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post #3 of 12 Old 04-03-2017 Thread Starter
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Re: Yanmar Hydrolock

I let it run for about half an hour and get warmed up. The engine is pretty low, probably about even with the water line. This is the first time it's happened since I've owned the boat ~4 years. I'll definitely change the oil, thanks for the advice.

It's a Peterson 33 Chita, 1978. We just had the engine overhauled last Summer and aside from some vibrations and chewing up a belt, it's been running like clockwork since.
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If the engine has been sitting for awhile..I'll open the compression releases and spin the engine a couple times..
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Re: Yanmar Hydrolock

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I let it run for about half an hour and get warmed up. The engine is pretty low, probably about even with the water line. This is the first time it's happened since I've owned the boat ~4 years. I'll definitely change the oil, thanks for the advice.

It's a Peterson 33 Chita, 1978. We just had the engine overhauled last Summer and aside from some vibrations and chewing up a belt, it's been running like clockwork since.
Trace your exhaust system.. I'll bet that at some high point there's a small tube running off to a cockpit drain or some such - that will be your vent on the antisyphon loop. It's likely plugged if the first two scenarios above are unlikely. If you have a proper vented loop (a vertical U-turn in the plumbing) it will have a vent fitting that probably needs attention.

If this is your issue it could happen again if you don't close the through-hull between runs... and could happen while sailing once you stop the engine...
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".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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Re: Yanmar Hydrolock

I once had this happened and thought the same thing with the starter going up or a weak battery.

Was at anchor and brought up the anchor as it had a float line on it, happened to also be my dinghy lift line to hoist it on the front deck. Once I retrieved the line i lowered the anchor and went to the cockpit and pulled the stop pull knob. In my haste I pushed in the stop knob on the last bit of engine rotation and the engine sucked in sea water from the exhaust.

Never thought it could happen and the BoatUS guy was not that knowledgeable, and i had not read up about it as of then. Needless to say after a tow back to my marina and a sleepless night, tried the engine in the morning after full night charging the batteries on shore current, same result.

After Googling and reading that this can be a fairly common thing I found the 3 (3GM30F) decompression levers, flipped them to open, turned the engine by hand as it could spin, turned over the engine by starter from about 10 revolutions and shut the levers and it started right up.

Let it warmed up, checked the oil for water and said my thanks that no rods were bent.

Make sure your engine is ALL the way stopped before pressing in your stop knob.

Jeff
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post #7 of 12 Old 04-04-2017
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Re: Yanmar Hydrolock

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Trace your exhaust system.. I'll bet that at some high point there's a small tube running off to a cockpit drain or some such - that will be your vent on the antisyphon loop. It's likely plugged if the first two scenarios above are unlikely. If you have a proper vented loop (a vertical U-turn in the plumbing) it will have a vent fitting that probably needs attention.

If this is your issue it could happen again if you don't close the through-hull between runs... and could happen while sailing once you stop the engine...
I think you sum the causes up, nicely. On the last potential cause of hydrolocking - a plugged anti siphon vent - what do you think is the least problematic anti siphon vent?

The loop with a built in vent is typical(I just installed one on a new exhaust). But once installed, there's no way to know if it's plugged without disassembling it. Are some types of these vents less prone to clogging?

The vented loop with a small hose off the top can be checked visually but that set up isn't possible on all boats.

Tom Young sailing a 1961 38' Alden Challenger, CHRISTMAS out of
Rockport, Maine.
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Re: Yanmar Hydrolock

Don't know the answer to that, Tom.. Nauticat, for instance, pipes the vent overboard amidships, creating a telltale 'pisser' just below the pilothouse doors, similar to an outboard's cooling telltale.. pluggage is pretty obvious if you're watching. (a marina neighbour Nauticat didn't notice the flow had stopped and had a hydrolock in a remote cove)

Boats with decompression levers will have an easier time recovering from this that those without - and also those with a drain plug on the waterlift. Without a decompression lever I suppose you'd have to pull the injectors to clear it, assuming you haven't done serious damage at that point.

Ron

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".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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Re: Yanmar Hydrolock

Some boats with stern exhaust can ram water up and over any riser system if conditions are right. Like a big following sea..A transom valve will prevent,. rubber flappers can be nearly useless A pisser (without a looping high spot.) edit for clarification The discharge hose has to be looped above the wl and small tube goes up from there so can suck/drain back down. in good and frequent observation is almost foolproof (winter wasps and cocoons) A drain in the aqua lift muffler is easy to install and may prevent a world of pain. My spring loaded shutoff released too soon ,,bent 2 rods on a new big Izsuzu .Just sayin. Decompressers are so handy Use em if you got em

Last edited by Capt Len; 04-05-2017 at 12:48 AM.
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Re: Yanmar Hydrolock

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Don't know the answer to that, Tom.. Nauticat, for instance, pipes the vent overboard amidships, creating a telltale 'pisser' just below the pilothouse doors, similar to an outboard's cooling telltale.. pluggage is pretty obvious if you're watching. (a marina neighbour Nauticat didn't notice the flow had stopped and had a hydrolock in a remote cove)

Boats with decompression levers will have an easier time recovering from this that those without - and also those with a drain plug on the waterlift. Without a decompression lever I suppose you'd have to pull the injectors to clear it, assuming you haven't done serious damage at that point.
Friends of mine hydrolocked the engine on a boat they had owned for just a year.

The mechanics spotted the problem: When the ignition energized the starter, of course it just clicked. But they could see just a bit of movement, then bounce back. "Hydro-locked", they told my friends. Sure enough, the newish Yanmar was full over water. The mechanics were pretty thorough pumping it out, changing the oil several times.

They added a riser and a either added or raised the vented loop.

Several theories about why it happened, but they never knew for sure.

The stern outlet on the boat had a flapper valve. That made me a little suspicious the outlet was low.

Hope it's fixed!

Tom Young sailing a 1961 38' Alden Challenger, CHRISTMAS out of
Rockport, Maine.
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