# Fresh water flush Yanmar diesel



## gotbaumb (Jul 21, 2003)

Can anyone tell me how to fresh water flush my 1985 G3 27hp Yanmar diesel. It''s not circulating enough water to keep the engine from overheating. 

I have cleared the raw water intakes on my saildrive, checked the pump hose to make sure its clear, pulled the water pump and inspected the impellar and looked for debris, and the water still trickles out.

The only other thing i can think of is buildup in the engine.

Any and all thoughts welcome. 

Thank You, GG (Charleston, SC)


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## knothead (Apr 9, 2003)

I''m a rigger, not a mechanic so I don''t claim to know what I''m talking about but a few years ago I installed a y-valve on my salt water intake just after the strainer and connected a hose which I ran into the bilge. I have a 10 hp salt water cooled Yanmar and what I did was partially fill the bilge with fresh water before I went out and then suck it back out with the engine when I got back to the dock. I figured it couldn''t hurt to have fresh water sitting in the engine between sailing trips rather than salt water. The bilge was kept clean that way too. Like I say, there may well be a valid reason why this is not a good idea or doesn’t help anyway, and I would be interested to hear others thoughts.


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## knothead (Apr 9, 2003)

Actually, I wonder what would happen if I sucked some vinegar into the engine and let it sit for a few days.


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## ssmith8523 (Sep 11, 2002)

I suspect your heat exchangers on perhaps both the fresh and raw water sides need to be de-scaled, especially if zincs have not been maintained. You can remove them and have them descaled in an acid bath. I had an overheating problem with my 25hp Westerbeke, and the mechanic pulled the hose off supplying water to the freshwater exchanger and blew air into it, and declared it almost plugged. He then grabbed a bottle of mild oxalic acid solution , held the hose straight up and poured the solution in, counted to 10, then flushed it out with water. Not something I would have the nerve to do myself! You may want to check your thermostat first to ensure it''s working properly.


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## Fessalo (Oct 4, 2011)

I would definitely check the heat exchanger intake tube. Beta Marine suggested this to me after I experienced the same thing and sure enough it was half plugged with small debri and remnants of anode and you cannot detect this by the amount of water coming out...it's just that the water coming in basically goes straight out without circulating efficiently where it should.


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## JimsCAL (May 23, 2007)

Is this engine raw water or fresh water cooled? Sounds like blockage in the raw water system, which could mean the engine (if raw water cooled) or the heat exchanger (if fresh water cooled). Is a strainer installed in the inlet? If not, you could have debris blocking the passages. A backflush with fresh water may help if that's the case. If the engine is raw water cooled, you could have scaling and then you may need a flush with Rydlyme Marine or oxalic acid.


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## Tim R. (Mar 23, 2003)

Thread is over 8 years old. hopefully solved by now.


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## Seaduction (Oct 24, 2011)

treilley said:


> Thread is over 8 years old. hopefully solved by now.


Good Point!!


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## JimsCAL (May 23, 2007)

Ah well. Fooled again!!


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## Capt Len (Oct 9, 2011)

Good advice doesn't improve with age but neither does it deteriorate.I find these old threads a good read.


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## jkimberly (Jun 18, 2008)

+1


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## raranovich (Sep 11, 2007)

Just the answers I was looking for, I have the same problem in a Yanmar 2QM20 I am rebulding. Will try to descale it with oxalic acid.


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## chuck711 (Dec 25, 2002)

*Rydlyme for Yanmar cooling systems*

Rydlyme is the preferred choice for Yanmar cooling systems.
Too strong an acid will eat the exchanger and you'll find yourself with an expensive part to buy.

The heat exchangers found on Perkins,Universal and Westerbekes are much more durable.

However more care is needed on Yanmar Heat Exchangers

I prefer to dissasemble the heat exchanger.
Physically remove all blockage then soak in Rydlyme.
Works every time


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## LakeSuperiorGeezer (Oct 8, 2010)

Engine corrosion is complex. Look at this: Corrosion in Salt Water Marine Engines


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## chuck711 (Dec 25, 2002)

*Overheating*

Saildrives have a reputation for restricting cooling water flow due to growths
and need to be cleaned out from time to time.


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## mitiempo (Sep 19, 2008)

Rydlyme is hydrochloric acid based with added wetting and penetration agents. I will be trying it on my Yanmar in the near future.


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## RichH (Jul 10, 2000)

RydLyme is a *buffered* hydrdochloric acid. The buffering agent prevents the reduction of the normally formed protective 'black' (ferrous) rust into destructive 'red (ferric) rust ... so that you can descale the carbonate formations ... and with minimal attack of the engine's base metal. Simple speak: RydLyme and other buffered descaling agents remove the 'insoluble salts' but not (much of) the 'metals'. Straight unbuffered HCl will bore through the carbonates, through the 'rust' and into the metal ... and since cast iron is typically a 'stratified' casting (like an onion) once you penetrate one of these 'onion layers' you promote 'slab rust' - large 'plateletts' of ferric rust that can loosen and migrate further into the engine and exhaust manifold and can cause partial or total blocking of the cooling circuit. 

Oxalic is 'too weak' an acid to adequately react with the formed carbonates .... the 'reactivity' of oxalic vs. carbonates will require an immense amount of 'oxalic' or 'vinegar' to do the job.


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