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Old 07-04-2020, 01:05 PM   #1
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Raw water motor flush

Hello all,
I have seen a thread where motor Flushing was discussed but I can't find it now so I want to kick myself but anyway I have a Perkins 6.354T that wants to heat up too much. It takes an hour or so but will go to 200 and beyond. My first guess is strainer. Second is sopped up passages. Third is stuck thermostat. I have a new heat exchanger and I had a raw water leak a few months ago and there is plenty of raw water pressure. T Stat is easy to get to. For you diesel old salts out there, any ideas?
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Old 07-04-2020, 01:33 PM   #2
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If you are concerned about a scale build up then you might try Barnacle Buster for flushing the raw water side. You can do a recirculating system or just suck it in and let it sit for about 6 hours and then start the engine and it will get expelled. I did it to my engines a couple of years ago and saw a drop in temp of 5 degrees on one engine and 10 degrees on the other engine.
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Old 07-04-2020, 02:42 PM   #3
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Depending on what you mean by "flushing"??
Freshwater flushing after running in saltwater is used to prevent future cooling issues from developing (as early as they might otherwise). It will slow down the ravages of saltwater exposure often called "marine age" (and actually has little to do with engine hours and actual age), and will extend the time between the still needed "full service" of the cooling system.
Flushing with BB or other acid like products is really a temporary stop gap measure to obtain an immediate improvement in cooling performance, but is not a full service measure. Those who think a BB flush is servicing the system are taking big chances in my opinion. Components corrode in the saltwater environment, and for example the gear oil cooler could develop a leak allowing saltwater into the tranny!! You won't know until it happens and your tranny is now being lubed with a saltwater mix. Fully servicing your cooling system usually involves: removing all of the saltwater components for an off engine cleaning, servicing, and very important pressure test (of each component); replacing the thermostat and pressure cap; pressure testing the coolant side; flushing and changing the coolant. This type of servicing is particularly important if your engine has a saltwater cooled aftercooler. 200 and beyond is not good! Running a overheated engine could lead to more serious damage.
If you don't know when, or it has been over 5 years since your last "full" service, I would suggest doing a full service now, followed by a regular freshwater flush routine to extend the timeframe before the next cooling service is due. JMHO.
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Old 07-04-2020, 04:32 PM   #4
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Is this a new to you boat? Does it seem to be pumping out as much water out the exhaust as usual? If not may need the raw water impeller changed. It could very well be the thru hull, especially if there is a hull strainer on the out side of the hull. Critters can take up residence there and obstruct the water flow.

Does it run at normal temperature for awhile before going over 200? If so I would think the thermostat would be ok. For it to cause the overheating it would need to fail in the closed position, in which case it would overheat as soon as the engine warmed up.

If the heat exchanger is new the passages should be for the most part clean.

Fan belts ok? The one driving the fresh water pump not slipping?

My guess would be the sea strainer or hull strainer.
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Old 07-04-2020, 05:46 PM   #5
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Gaylord,
I focused in on your "flushing" request, as I assumed (Oops) that this was a "new to you" boat. If your system has been recently (3 or 4 years ago) fully serviced, it might not be needed yet. However, other things can lead to a reduction in raw water flow. For example bits of impeller or bits of anode can plug up the small passages leading to this type of problem. Salt buildup or the calcium (small shell pieces) buildup from tiny sea critters, slime, etc. can all help to block the passages. That is also why a full service might be best? Definitely check out the sea strainer (does the lid seal properly) and even the thru hull for possible blockages. Also check the impeller for damage as well as the pump itself for signs of damage (scoring of the plate, leaking seals, interior damage, etc.). Russell had good ideas.
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Old 07-04-2020, 08:18 PM   #6
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This engine needs a compression test. It sounds like a blown head gasket.
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Old 07-05-2020, 03:08 PM   #7
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Lots of good ideas so far. My goal will be to ultimately do the little and cheap stuff first and if necessary graduate to the more serious stuff. It's in the water now where it will stay unless a hurricane comes and I have to pull to the hard.
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Old 07-05-2020, 06:26 PM   #8
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Read my tome below about heating up while running. If you have specific questions ask and we will try to fill in.

A flush of the COOLANT side can be done using flushing chemicals. Cummins / FLeetguard makes one called Restore. Directions are on the bottle. It will require several clear water flushes to remove the chemical afterwards.

Barnacle Buster can be used can be used on the seawater side. Just be carefull as these are strong chemicals and again must be flushed afterwards.

However there are MANY other causes of heating up which I tried to cover as this problem comes up frequently.
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Old 07-06-2020, 04:56 AM   #9
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Thank yo u C electric. Look forward to reading your time on testing.
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Old 07-13-2020, 08:28 PM   #10
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Older Perkins has cast iron exhaust manifolds, some models run raw water through them, such a bad idea!
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