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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 07-16-2007
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Yanmar 2GM overheating

Ran my 25 year-old raw water cooled 2GM for about an hour, against 35 kt headwinds, and the water temp alarm came on. Don't have a tach, but I was trying not to push the engine too hard, and was only doing a couple of kts, into the wind/waves. Shut engine down, removed hose at exhaust elbow, and got a dry poof of smoke. Started the engine, and got water immediately - which was obviously hot. Put the sails up and let the engine cool for several hours. Ran again for a few minutes to get on mooring.

I will take the exhaust elbow off, to look for blockages, but as the engine was in salt water for 25 years, should I try to flush with oxalic or muratic acid. If so, do I need to take the thermosat off and use a drill-pump to circulate, or can I run the engine until warm, change the water intake hose to the acid bucket and run the engine for a couple of minutes - and let sit.

I have previously checked the impeller, which seems fine, and norammly, water flow seems normal. The exhaust / water exits underneath the stern, so you can't see the water flow from on board. I don't know if the was flow reduced, or stopped totally when it overheated.
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Old 07-16-2007
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Certainly look for blockages first (and look for any partial blockages in your intake line...from thru hull to strainer and strainer to impelller. )...but if you DO decide to give it an acid cleaning...run the engine until warm, change the water intake hose to the acid bucket and run the engine ...

Just run the engine long enough to see the acid mix coming out of the exhaust...then let sit for about 20 minutes before re-starting and letting run. You might need to pull the heat exchanger but the acid bath is worth a try first.
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Called every hardware store around. Can't find oxalic acid. Waht are thoughts on using Fleetguard's product Restore Haevy Duty Cooling system cleaner - says it removes scale.

Anyone used it before??
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Thanks Cam! I don't have a heat exchanger (Raw water cooled) and am not even connected to the water heater, at the moment.

When I took the cooling hose off of the exhaust elbow, and re-started the engine, there seemd to be sufficient flow, at that time.

I have been told to use Muratic acid, by a marine dealer, but have read that this may cause damage to the metal, that could be avoided wiuth oxalic acid - which I can't find in stores.

How much damage would Muratic acid do to the metal, or other parts. I don't mind changing the impeller, if necessary, but want to avoid major work.
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My local hardware store carries oxalic acid crystals in box. You might check a paint store. Muriatic acid is much stronger than oxalic, so make sure you dilute it well. ON-AND-OFF sold for cleaning boat bottoms is essentially muriatic (hydrochloric) acid. I have done this several times on my 25 year old Universal 5411. I remove the thermostat, clamp the hose going to the exhaust, and then circulate the warm acid with a 12V pump for a few minutes, let it sit for 10 minutes, repeating for a total of about an hour. You should also try backflushing the cooling passages. That will probably dislodge some stuff.
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I've recently found oxalic acid at the hardware store, as well. It's sold as wood bleach.
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I have tried all hardware stores in my area, big and small (Home Depot, etc). No luck.
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Removed exhaust elbow, which looks fairly new. Exhaust side had soot build-up, but it was not blocked - could blow easily through the water inlet. Cleaned with acid anyway.
removed thermostat - had some black rubbery gunk on the front. Cleaned with acid, and tested - opens fine in hot water.
Flushed / soaked system in Muriatic acid solution. Acid came out black after soaking, but not sure if it was more than normal.

what seems odd is that the water pump will pump normal amounts of water through engine, when connected to the seacock - which feeds somwhat pressurized water to the pump. But when I try to pump water from a buck instead, it does not seem to pass water through the engine. I have checked teh impeller, which looks good. Is this normal, or is it a sign that the pump is worn out?

Advice please!
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Old 07-17-2007
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Northeaster,
You could give try Mack Boring, or Torresen. They could probably give you some pretty accurate info on cleaning the blocks cooling passages.

Sailing - Lake Michigan, The Great Lakes and Around the World - Sailboat Specialists - Providing Sailor's Needs Around The Great Lakes and In 75 Countries Around The Globe -- Torresen Marine, Inc.

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If there is wear on the sides of the casing and cover of the pump, there may be excessive side clearances and the impeller will not seal and will not be able to lift water any vertical distance. That could explain why it pumps from the seacock (flooded suction?) and not pull from a bucket where it needs to develop a slight vacuum to lift the water. I was able to get my original Sherwood raw water pump to work again by removing the cover and filing it smooth where the impeller had worn grooves.
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