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Old 19-04-2015, 06:44   #16
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Re: How big of a deal is hydrolock?

This is interesting. I have a couple of questions maybe someone can clarifying some basic language. We have a yanmar 39hp which I assume has two cooling systems, seawater and coolant. What does the seawater cool, and what does the closed system coolant cool? How can seawater enter the cylinder? I guess the seawater comes out with the exhaust so it returns through the exhaust system as far as it can and through the exhaust valve ?
Winterising - I guess it's best to flush the raw water system with fresh water, how does the bucket system work? How long can an engine be run with no raw water?
Thanks
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Old 19-04-2015, 07:04   #17
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Re: How big of a deal is hydrolock?

Ok I found ten answers to the first question here, still curious about how hydrolock can happen. How did your happen brown?


Engine Cooling Systems Explained

Our last contest consisted of selecting the order of things to check to troubleshoot an overheating engine with a "raw water" cooling system. A few of our viewers asked me to explain just what a raw water system was and how it worked. Raw water refers to the water that the boat is floating in. It makes no difference whether it is salt or fresh, both are used to cool the engine. The process starts by drawing water into the engine through a seacock fitting and pumping it through the engine's water jacket and ports by way of a mechanical water pump.

In a raw water system the water is drawn up through the seacock by the water pump. The water flows through the engine and directly out the exhaust. This cooler water absorbs heat from the engine to help keep it cool.

Most newer marine engines use an enclosed cooling system. This means that there is a small tank on the top of the engine that uses a combination of fresh water and coolant. This fresh water is circulated through the engine and through a heat exchanger. The fresh water, in this system, absorbs the heat of the engine. Raw water is still drawn up through the seacock but only flows through the heat exchanger jacket. This cooler raw water absorbs the heat from the fresh water through the heat exchanger jacket and is then pumped out the exhaust.

The advantages of the enclosed system over the raw water system are extreme, especially if you are operating in salt water. Salt water tends to build up a corrosive scale when the engine operates above 140. In the raw water system this scale is building up inside the engine's water jacket and ports. When the scaling builds to the point that water flow is restricted the engine starts to overheat. At this point you are probably looking at replacing the engine.

In the enclosed system, the water that flows through the engine's water jacket and ports is the fresh water and coolant. The only part the raw water flows through is the heat exchanger. The same scaling occurs however. When water flow is restricted and the engine begins to overheat you may be able to "acid boil" the scale out of the heat exchanger and continue to use it. The worse case is that you would have to replace the heat exchanger. This would be much less expensive than replacing the engine.

Other components of the cooling system, whether it be raw water or enclosed, are the seacock, sea strainer, hoses and clamps, belts and water pump impeller.

The seacock is a through-hull device that allows water to enter the hull from the outside. This device has a handle that allows you to shut off the water flow if you have a problem such as a loose hose clamp or cracked hose. You should test the seacock shut-offs monthly to make sure they are operable. As a backup safety measure you should have a soft, tapered, wooden plug (called a bung) of the size of the seacock tied to the seacock. In case a hose parts and you can't operate the shut-off you can put the bung in the seacock to stop the water flow.

The next inline part of the engine cooling system is the sea strainer. This is a device through which the raw water flows and is designed to filter out debris, sand, leaves, etc. before it gets to the engine. This device works much like a swimming pool skimmer. There are several kinds of strainers but all have a removable filter or screen which should be checked and cleaned or replaced on a regular basis.

Hoses, clamps and belts are vital to the cooling system and should also be checked periodically. Every time you check the oil, which should be done before each start-up, you should visually inspect hoses, clamps and belts for wear. All hoses that are below the waterline should be double clamped. This will help prevent water from entering the bilge should one of the clamps fail. If you find a corroded clamp, a pinched or cracked hose or belt, they should be replaced immediately. Be sure to replace the hoses with the same size diameter, length and temperature requirements that the manufacturer suggests.

The raw water pump, which is driven by a belt on the engine, contains an impeller which makes the pump operate. It is usually fairly easy to access the impeller to inspect or replace it.

In the enclosed system, a commercial coolant (antifreeze) should be added. This will prevent the fresh water from freezing and damaging the engine in cold climates and also will help prevent corrosion build-up in the fresh water system. Normally you would use the coolant and fresh water in 50/50 mixture. In colder climates you may want to increase the coolant percentage.

In summary, the direct, raw water system circulates water through the engine water jacket which flows through the block, head, manifold, etc. This water absorbs the heat from the engine and is exhausted overboard.

The enclosed system circulates fresh water and coolant through the engine water jacket and through a heat exchanger. This fresh water absorbs the heat of the engine. The raw water is also pumped through the heat exchanger where it absorbs some of the heat of the fresh water and is again exhausted overboard.
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Old 19-04-2015, 07:09   #18
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Re: How big of a deal is hydrolock?

The fresh water circuit circulates coolant from the engine block to a heat exchanger. The heat exchanger is cooled by sea water that is pumped to a nozzle I'm the mixing elbow where it combines with exhaust gas from the exhaust manifold. If sea water flows into the mixing elbow while the engine is not running (starter cranking but engine not starting or water siphons in while engine is off) sea water will fill the exhaust system and flow backward into the exhaust manifold and through the exhaust valves into the cylinders.
To flush for winterizing remove the sea water intake hose from its through hull and place in a bucket of fresh water. Run engine until bucket is almost empty. An engine can run without sea water for a very short time (seconds) before the sea water pump impeller is destroyed. It takes a while longer for the engine to overheat and begin damaging other components.
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Old 19-04-2015, 07:24   #19
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Re: How big of a deal is hydrolock?

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Originally Posted by brownoarsman View Post
I still need to give it a good long hard run. I spun the water out right away, and started her up until the overheating issue caught up with me, then couldn't start it again. After spending a couple days trying to fix the starting issue, I flooded the cylinders with wd40 and spun that out. Starts up like a dream now with no audible damage. Hope it's not just the oil coating! However, still putting the engine back together and waiting for parts after taking everything off before I run it for more than a couple seconds.

Here's another question on the subject. When you spin the water out of the cylinder, where does it go and how does the rest of the water get out? I assume the excess starting water enters through the mixing elbow, fills the lift pump and works its way back up the riser (though shouldn't this not happen if the riser is above the level of the exhaust hose)? Don't you need exhaust to force water out of the lift pump? So when turning the engine over by hand without firing, wouldn't you just be putting water into water? Where does all the excess go?



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You can only "spin" water from the cylinder by removing the injectors, or glow plugs on some engines, or using the decompression levers if so equipped. When you "spin it out" it ejects through the glow plug or injector hole or through the open valve if you used decompression. The glow plug or injector are usually the best option as it will also allow you to oil soak each cylinder from above (Marvel Mystery Oil works pretty well here) if the salt water sat in there..

If you expelled it without doing any of the above you have leaky valve seats or you blew it by the piston rings and into the crank case...
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Old 19-04-2015, 07:56   #20
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Re: How big of a deal is hydrolock?

"I then politely reinforced to him that under no circumstances should he connect pressurized water to his raw water intake........"

This is for a normally plumbed running engine because you fill the water lift muffler and it finds its way back up the exhaust and into the cylinder, correct?

The reason I ask is I am going to convert my MD7A to fresh water cooling. Part of my plan in doing that is a serious amount of flushing out the engine ahead of time to try and clean out the cooling passages. My plan is to take out the thermostat and impeller. Removing the hose from the water injection elbow and replacing it with a longer hose that will reach outside of the boat. Then flush with citric acid (multiple times) and lots of fresh water. I was planning on using pressurized water on the inlet side and just letting it flow through the engine (engine off) with the outlet on the thermostat housing draining outside of the boat. Then probably doing the same thing in reverse with the pressurized water feeding into the outlet on the thermostat and backwards through the engine and out the seawater inlet. Repeating until the water runs clean.

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Old 19-04-2015, 08:10   #21
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Re: How big of a deal is hydrolock?

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I was planning on using pressurized water on the inlet side and just letting it flow through the engine (engine off) with the outlet on the thermostat housing draining outside of the boat. Then probably doing the same thing in reverse with the pressurized water feeding into the outlet on the thermostat and backwards through the engine and out the seawater inlet. Repeating until the water runs clean.

Shawn
Recommend you allow the engine pump to lift the water into the engine from a bucket or other open container. Use the hose to supply the container...no chance of flooding the engine.

No need to back flush...flow n one direction is as good as the other.
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Old 19-04-2015, 08:11   #22
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Re: How big of a deal is hydrolock?

Hi Monte-I hydrolocked by spinning the starter motor four times for five seconds each. Didn't think that would hydrolock it but there it is.

Mainesail-I have a decompression lever, thankfully, which I used. Unfortunately, the glow plugs needed tools I didn't have on board (just bought the boat), so I only got those off and pickled the cylinders about a week later I'm hoping the three minutes of running directly after the hydrolock before she overheated burned out any remaining water and coated everything in protective diesel. She's fired up since then, and I'm really hoping the new pump solves my raw water issue. By the way, thanks for all the great how-to's!


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Old 19-04-2015, 09:35   #23
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Re: How big of a deal is hydrolock?

"No need to back flush...flow n one direction is as good as the other."

I was mostly thinking there if anything clogs up from what was loosened by the citric acid.
The boat engine was starting to overheat last year as the passages where getting gunked up, a fairly common problem on the MD7A.

I have a spare MD7A and have been cleaning out the exhaust manifold on that one to swap onto the engine in the boat. I've been amazed at how much gunk has come out of that after multiple cleanings. I want to get as much of that out of the system before closing it off for fresh water cooling. I don't want it working loose and clogging up the heat exchanger. I've considered putting a strainer into the fresh water circuit for that reason but not sure if they would handle the heat.

Shawn
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Old 19-04-2015, 09:47   #24
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Re: How big of a deal is hydrolock?

I used to sail on a boat that would frequently flood the engine thru the exhaust thru hull when conditions were rough and the the seacock was left open.

The owner would turn over engine using a wrench in a backward rotation. This ejected the water locking the cylinder. He then started up with little issue. Just changed the oil and when on. This engine lasted for more than 15 years while cruising.
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Old 19-04-2015, 10:08   #25
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Re: How big of a deal is hydrolock?

It depends a lot on the engine. (and a little luck).

I was hove to in a nasty gale in the Tasman, sailing from NZ to OZ. both the main engine and my gen set hydrolocked. Starting them, it bent two rods in the main engine, a Volvo TAMD 61A, but the generator, a Northern Lights 8KW, I pulled the injectors and spun it, put them back in and cranked it up and it ran fine.

The gen set hydrolocked twice more, and each time I pulled the injectors, spun it then started it and had no problems with it. I am not sure if the starter motor was powerful enough to bend the rods on the main, or it fired on the clear cylinders and the force bent the rods on the water bound cylinders. I ended up putting a shut off valve on the exhaust for both engines for when I had to heave to in the future.

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Old 19-04-2015, 10:41   #26
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Re: How big of a deal is hydrolock?

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So it's really the degree of water in the cylinder? I had that distinct hydrolock thud three times before I figured out I had made a big oops. But, no significant lasting damage apparently. I guess a little or a lot of water will both keep the engine from turning over, but a lot of water is more likely to blow the engine up?


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Brownoarsman - How do you know you had "that distinct hydrolock thud three times"? Your description sounds like the thuds may have been pre-ignition - where the cylinder fires before the piston is adequately on the way down. In a gasoline engine this is usually caused by an error in the timing of the spark. Also, low octane fuel may cause a similar sounding knock. If the engine is diesel the combustion is initiated by the heat of compression igniting the fuel as it is injected. The cause may be an error in the timing of the injectors. Another cause may be that fuel is getting into the cylinders by some other means - like through the air intake. I've heard of things like spraying WD-40 (or other flammable) near the air intake. Or even not adequately drying the intake manifold after cleaning it with a flammable liquid.
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Old 19-04-2015, 13:21   #27
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Re: How big of a deal is hydrolock?

FWIW, the older engines that just used raw water cooling, actually lasted forever. But they ran much cooler in order to eliminate the build up of scale that occurs over 140 degrees. Running cooler is not as efficient for a diesel, so there was that disadvantage. But the engines were built to take salt water and had zincs. The best mechanic I ever met said "people only began putting in heat exchangers when Americans insisted on hot water for their showers", since the coolant can also heat the hot water heater! And, at least on my engines (Yanmar 4JH3E), the heat exchanger is a very expensive thing to replace, more even than the injection pump.
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Old 19-04-2015, 13:29   #28
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Re: How big of a deal is hydrolock?

Depends on the circumstances of the lockup.
If the engine hydrolocks while it is sitting not running and only the starter or hand-crank was used to attempt the engine over, it is very possible to drain out the liquid and simply flush out the cylinders with compressed air.
I expect the corrosion created is the most damaging of possible problems.
Most starters and few arm muscles can generate enough torque to deform internal engine parts.
If the engine hydrolocks while the engines is running, it will destroy its self .
Connections rods can be bent and rod tossed through the engine block.
The old Detroit Diesel 71 Series really did not tolerate hydrolock when running, probably about the only thing that would kill them.
Hydrolock is not uncommon in industrial equipment that uses vertical exhaust systems, when left out uncovered in the rain, the water causes many issues with these engines.
But it is rare to get a total engine failure unless the rust created by the water intrusion is not cleaned out asap.
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Old 19-04-2015, 13:47   #29
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Re: How big of a deal is hydrolock?

Small marine diesels were built for raw water cooling. On the Volvo MD series all parts that came in contact with salt water were replaceable and could be rebuilt in place in the boat. Think these engines were designed to some Life Boat Specification so were usually hand crankable. Don''t know what the original A4 block was designed for but they were so overbuilt that they'll last virtually forever in saltwater. Not sure about the A4 but the diesels didn't use zincs to prolong their life, just robust design and replaceability along with a lesser corrosive lower coolant temperature.

Marine conversions like the Perkins, Yanmar, etc were based on tractor/industrial engines and not designed to run with raw water cooling. They will go a long time before rust eats them up, however. Most higher hp power boat engines were Detroit car engines. The blocks were cheap so they were throw away engines when they rusted up.

For an engine that is not designed for salt water cooling, the cost and complication of freshwater cooling is cost effective IF you plan on running the engine for a long time. The 'fun' boat jockeys that terrorize in anchorages and slips with their wakes probably don't think engine longevity beyond the coming summer so initial price was what the boat builders went for. As the cost of engines and their probable useful life expectations have gone up, fresh water cooling has become de riguer. Besides you get a hot shower out of the deal.
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Old 19-04-2015, 13:48   #30
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Re: How big of a deal is hydrolock?

Had the cylinders full of salt water after a night of corkscrew seas from behind on my new to me boat (coast of Baja). No flapper valve on the exhaust. Tried to start the engine and it sheared the spiral teeth of the hard to replace bendix gear. I build a crank handle to fit the belt pulley, hand cranked the water out, filled the engine with oil and hand cranked lots more before changing the oil. Hand cranked daily for more that a month by which time we had sailed into Cabo and ordered a replacement from England (5 weeks). Fortunately I found a Mexican mechanical artisto who welded up the bendix spiral gears and machined them back down. I got her started up and after the huge cloud of smoke cleared she took me around the world on that repaired original bendix.
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