Hydro lock unexplained

Stu Jackson · Nov 29, 2011

M25 engine

You mentioned: went to start the engine and nothing happened - no ignition - no turnover. It became apparent that somehow the engine had experienced a hydraulic lock, sufficiently damaging as to require a rebuild

No ignition, no turnover COULD BE a broken fuseholder between the start button and the starter solenoid. Happened to me. Perhaps you got the hydrolock diagnosis AFTER that was ruled out - you didn't say.

...riser not high enough to break siphon), no one knows for sure why it happened - remember there was absolutely engine turnover. I need to ensure this does not happen again...

What it sounds like is that your anti siphon valve failed. The valve is on the water line from the HX to the exhaust riser nipple. Most M25s I've seen have a 5/8" anti siphon loop with a small duck billed rubber diaphragm which does require servicing - just a simple clean out. If it clogs, it cuold allow water to backfeed into the engine. It is there to prevent that from happening.

Stu Jackson · Nov 30, 2011

Genesis1986 said:
Do you think a larger water box would make sense? I don't believe that the starter is the issue, but that water was already in the cylinders and was completley unable to turnover.

Don't quite know how a larger muffler would help. Unless your PO put a teacup there. Wanna explain?

Has anyone suggested using the decompression lever to try a turnover? I don't use the decompression lever, ever, even as a fallback, but lots of C30 skippers have used it on this engine based on many Mainsheet articles. I am not proposing it, just asking if anyone else has.

Water Runner · Nov 30, 2011

My understanding of hydro-lock in reference to an engine is when it 'ingests' water and 'locks up' due to water not being compressible.

If the engine was just sitting there AND ran the last time you were out and about then there is no reason to suspect it 'hydro-locked' while sitting still not doing anything.

I would guess that you have a power issue as others have said.
You can test this with a multimeter, one side on the switch, the other side of the multimeter on the starter checking for continuity.

weinie · Nov 30, 2011

Sounds a bit fishy. Hydrolock would be more likely if the engine was running and there was a mechanism to ingest water into the cylinders. I suppose sea water might flow in from the exhaust flap if the flapper was missing and there was a big wave of water hitting the transom while it was docked and the anti siphon valve was stuck shut.
Usually the engine stalling is the first sign of hydrolock (at least from my experience in cars).

Tom J · Nov 30, 2011

Actually, hydraulic lock is most likely to occur after the engine is shut down. Most of you trailor-sailors know that you shouldn't shut your vehicle engine off when you are launching/retrieving, in case you have backed down too far and your exhaust is in the water. In that case, if you were to shut off the engine, the engine would cool and the pressures in the cylinders would decrease, creating a partial vacuum, sometimes enough to suck water into the engine. Same thing can happen on a diesel engine with a wet exhaust. Most boats have the exhuast outlet above the water-line, but the water in the muffler and lines could be sucked back into the engine. Hence the anti-siphon valve in the raw water loop above the mixer elbow. My anti-siphon valve is easily accessed and has a plastic cap with the kazoo in it. Just occassionally rinse it in the galley sink. Also be aware that an engine that cranks too long before it starts can fill the muffler with water, increasing the chance of water ingesting into the engine. Follow your owner's manual instructions in this case.

rbmcintire · Dec 1, 2011

The precaution is to drain the Air-Lift muffler housing at its petcock before continuing "extended" engine cranking, but how much cranking would require a drain down?

Rob

Water Runner · Dec 1, 2011

Tom J said:
Actually, hydraulic lock is most likely to occur after the engine is shut down. Most of you trailor-sailors know that you shouldn't shut your vehicle engine off when you are launching/retrieving, in case you have backed down too far and your exhaust is in the water. In that case, if you were to shut off the engine, the engine would cool and the pressures in the cylinders would decrease, creating a partial vacuum, sometimes enough to suck water into the engine. Same thing can happen on a diesel engine with a wet exhaust. Most boats have the exhuast outlet above the water-line, but the water in the muffler and lines could be sucked back into the engine. Hence the anti-siphon valve in the raw water loop above the mixer elbow. My anti-siphon valve is easily accessed and has a plastic cap with the kazoo in it. Just occassionally rinse it in the galley sink. Also be aware that an engine that cranks too long before it starts can fill the muffler with water, increasing the chance of water ingesting into the engine. Follow your owner's manual instructions in this case.

That actually makes sense.
It just sounded like the OP was saying it hydro-locked while sitting in storage.

Tom J · Dec 1, 2011

rbmcintire said:
The precaution is to drain the Air-Lift muffler housing at its petcock before continuing "extended" engine cranking, but how much cranking would require a drain down?

Rob

The manual on my Catalina 310, with Universal M25-xpb, says to drain the muffler if the engine doesn't start after 30 seconds of cranking. This isn't really very practical, so I just close the raw-water seacock and proceed to crank in 30 second intervals (to protect the starter). Then, when the engine starts, the first mate quickly opens the seacock, or I hurry down and do it myself. So far, this hasn't hurt the impeller in thle raw-water pump, and it shouldn't, as long as the system is already full of water. I also have the habit of closing the seacock after I shut the engine down, especially if we are going to be away from the boat. This works for us, because I also check the seacock, oil level and belt tensiion before I start the engine, and my first mate is good at reminding me to do so.