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Old 03-04-2015, 20:15   #1
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The case of the intermittent water cooling system

For all the diesel sherlocks on the forum. Roughly every third time I start my engine (universal diesel 5411, raw water cooled, installed 1980), the water passages are clogged. Blowing out the water passages a few times fixes the problem, though it might take two or three blowout, start, shut off cycles. The issue isn't the impeller, that spurts water out fine when the hose is disconnected and the engine switched on. Similarly, I don't believe the issue is downstream of the block, as when water is flowing, it pisses out the exhaust like an Irishman after ten beers.
I've collected the blowout water from inside the block, and there are some little clouds of suspended rust which I'd expect in a raw water cooled engine, as well as some hard, but brittle, black bits that resemble very small pieces of shale, and when ground between fingers, leaves a bit of a black smudge.
There is a bit of a quirk with this engine as well. Rather than use a thermostat, two POs ago, the thermostat was replaced with a ball valve on the recirculating hose. Temperature is controlled by adjusting the valve at cruising rpm. PO left the valve closed all the time, and these problems started when I opened it to get the temp up (which caused the temp to rise to about 200 degrees before I caught it).
What do you think the issue might be? And how would you fix it?


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Old 03-04-2015, 20:34   #2
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Re: The case of the intermittent water cooling system

It might be running too hot. Sea water should not be allowed to exceed 145F. See this excerpt from Cruising World :

"A more insidious drawback to the raw-water system is that the engine must run cooler than it could with a closed system. Above 160 F, sea salt begins to crystallize inside the cooling-system passages. This not only accelerates corrosion but also, in extreme cases, can actually block passages. For this reason, most raw-water-cooled diesels have a thermostat set at 145 F, at least 40 F cooler than a closed system. Running at this relatively lower temperature reduces an engine’s thermal efficiency, so a raw-water system simply is unable to produce as much usable power as its closed system counterparts."

If I were you, I'd put the thermostat back in. A ball valve that you adjust when cruising? Seriously?
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Old 03-04-2015, 21:02   #3
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Re: The case of the intermittent water cooling system

The mystery here is whether we can accurately infer from oarsman's description why about every time he goes to start the engine, he has to blow out the water passages, whereupon he is able to start it.

The only clue is the black colored particulates, that moosh and leave a dark smudge on his fingers, kind of like decaying gasket material.

The white lumpy stuff is probably salts.

I'm no Sherlock, anybody out there want to take a flyer?

Good luck with it, brownoarsman.
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Old 03-04-2015, 22:49   #4
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Re: The case of the intermittent water cooling system

Hahaha, yes, that thermostat task is definitely on my list of to-dos. I have it, actually, under my settee. The engine has been in its present configuration for at least the last decade.
I had read that CW article as well, and it was the reason I was fiddling with the recirculating valve to raise the temp (engine is currently running at 125 which is too low). Maybe I should never have played with things that were working alright as they were.
If that hard brittle black stuff is decayed gasket (thanks Anne!), then the recirculating valve may still be releasing its years of accumulated gunk, though I had thought that closing the valve would have removed that possibility. I'll strip those hoses and the valve off and see what jewels they may be covering.
It is puzzling to me, and I haven't been using the engine much which may play into it. In the last two and a half weeks: once to reanchor in a storm, and then today to power through a narrow channel before dark fell tonight (that didn't work because the cooling flow was blocked again). I do feel I need the motor immediately in these kinds of situations, so would certainly like it to be able to run for more than a couple of minutes at a time!


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Old 04-04-2015, 01:53   #5
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Re: The case of the intermittent water cooling system

Brownoarsman,

The white salts may now be built up throughout the cooling passages, because it got run so hot it precipated them out of the salt cooling water. If that is the case, an acid bath will do the block a world of good. When you get the thermostat out, have a look with a tool like a dental pick, and see what you can feel in the passages. If blocked, the acid bath may help a whole lot. Jim did this with a big bucket, into which you direct both the exhaust cooling water, and with a hose for the intake. We used swimming pool acid. It boils around inside there and makes a racket. You keep doing it till it doesn't make noise any more.

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Old 04-04-2015, 02:15   #6
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Re: The case of the intermittent water cooling system

I, v had a couple of problems with my 1990ish Yanmar 3gm30 sea water cooled engine.
Over the years the flow from the exhaust steadily dwindled untill on the way back from the Isle of Mann with little wind I had a steady steam output.
The engine never failed but I began investigating and asking around.
Heres the list.
Changed the impeller. No improvement.
Checked the flow at the pump outlet, seemed fine. No Improvment.
Removed the thermostat, worked ok in hot water. Ran without. Still steamy.
Took the mixing elbow off, well encrusted with carbon, cleaned up. Still Steamy.
Filled engine water ways with brick cleaner acid, trawler mans advice, lots of bubbling, washed out. Still steamy.
Last straw, overheat alarm and clouds of steam coming into harbour. Closer inspection of pump, faces and body showing ware.New sea water pump. Better flow and little steam.
BTW, the smuts could be the the exhaust flexible hose breaking down as it is unable to handle the higher temp exhaust gasses if mixing is retarded. I,ll be keeping an eye for this this season.
Hope to have cured my problem but time will tell.
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Old 04-04-2015, 02:19   #7
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Re: The case of the intermittent water cooling system

Good one, centaur!

Oarsman, if you do an acid wash, remove the zincs, if any, first, and let us know what shape they were in. Some of those white bits could be fractured zinc bits.

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Old 04-04-2015, 08:09   #8
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Re: The case of the intermittent water cooling system

What sort of idiot would remove the thermostat and replace it with a manual valve?

What other stupid modifications might he have made?

I would restore the engine to the original configuration and flush the cooling system thoroughly. Acid cleaning may or may not be necessary. I would try without it at first.

The post above about raw water cooled engines running at a lower temperature is correct. Find out what thermostat is supposed to be in the engine and use that.
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Old 04-04-2015, 08:46   #9
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Re: The case of the intermittent water cooling system

yes I would go with a acid flush first, how many hours on the engine,
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Old 04-04-2015, 09:00   #10
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Re: The case of the intermittent water cooling system

The black particles that smudge are pieces of broken water pump impeller. It sounds like that engine has been Mickey Moused by amateurs. How long since a professional diesel mechanic has serviced it?
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Old 04-04-2015, 09:06   #11
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Re: The case of the intermittent water cooling system

Hi everyone, thanks for the continued advice! The PO did hook a freshwater hose up and flush the block every year.
The reason I wouldn't think it's salt buildup is that the problem is intermittent. If there was an actual clogging of the passages from buildup, wouldn't this non-existent water flow be a permanent thing? I couldn't identify anything inside the block itself that would act as a valve that might inadvertently close. Is there anything like that that might be the issue?
If it is just a very stubborn clog that sinks and then rises sometimes, the flush will certainly help. I'll run it through a bucket of fresh first and then try the acid bit. Thanks again!


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Old 04-04-2015, 09:22   #12
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Re: The case of the intermittent water cooling system

The engine has 2550 hours on it, so it is a bit long in the tooth.
The engine hasn't been serviced by a mechanic for years. If those black bits are pieces of an old impeller, then maybe it is just a stubborn clog that only presents itself sometimes and isn't blowing out.
Read Mainesail's overview of flushing the engine, and I'll need to pick up a small pump, so can't do it for a bit. I imagine I can't just let the exhaust run out hot without water or it would be a lot easier!


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Old 04-04-2015, 10:24   #13
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Re: The case of the intermittent water cooling system

Aren''t boats fun? My Yanmar 2qm15 has maybe 400 hours on a rebuild 5 years ago. It has a freshwater flushing tee which I use after every running. Raw water cooled. I replaced the idiot temp light with a mechanical gauge that starts at 100F. It never reads above the 100 mark. Of course the sea temperatures are usually around 57. The thermostat is marked at 85 and did open at that temp in a sauce pan of water on the stove. Underway the engine feels just a little warmer than body temp. Go figure. Engine runs strong and no smoke. Sips fuel.
I, too, always thought a higher temp was more efficient. Now I wonder.
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Old 04-04-2015, 10:37   #14
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Re: The case of the intermittent water cooling system

My smaller sailboat is an O'Day 28 with same Universal 5411 Universal, which by the way is made by Kubota and you can get the usual basic parts from any Kubota tractor dealer in a pinch. The boat originally did not have a raw water filter and with the Chesapeake Bay's jellyfish and shallow areas I started to have to flush out the engine's raw water system mid season. One thing I noticed was I could flush from the normal raw water pump direction and could get gunk out and clear water pretty quick, but when I reversed the flow and forced the water the opposite direction... a whole lot more gunk came out. Thinking it was now surely clean I went back and flushed from the original direction just to check and surprisingly a lot more gunk came out. I had to repeat this process about 10 times before the flush was immediately clean and stayed clean in both directions. I never tried acid, but may if problem returns. But since I added a raw filter to keep out the bigger things, I haven't had flow issues for 3 years.

FYI- There is an excellent marina operator/ diesel mechanic up on Lake Superior area I found on google search (Google: 'small diesel repair') that specializes in small diesels, especially the 5411. He has a fresh water/ coolant conversion kit for these small raw water engines for about $400 that that mounts right on the engine using existing bolts that will greatly increase useful life.


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Old 04-04-2015, 10:52   #15
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Re: The case of the intermittent water cooling system

I would check the wear on the back plate of the raw water pump. The raw water pumps are positive displacement type. This requires that the impeller edges fit tight to the front and back plate. Over time the back plate will wear down some. So will the front.

What happens is water is leaking around the edges of the impeller and the pump will not pump when that happens. Sort of like bad rings on a piston. It might even need a new pump installed.

I do agree a acid flush /recirc into a bucket to get the crud out of the block will help too. A fresh water flush is pointess. Probably a bit of too much pressure drop and a weak raw water pump.

Never run a raw water engine above 140 degrees as the coolant passages will lime up very quickly. Quickly as in weeks, not days.

It's elementary after all.
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