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Flushing of Raw Water Cooled Engine Circuit

Blitz

.
Jul 10, 2007
565
Seidelmann 34 Atlantic Highlands, NJ
As part of preventive maintenance which was never done before, and the boat has always spent it’s summers in salt water and winters with the engine winterized. I’m planning to flush out my Yanmar 3GMD engine with Rydlyme and had some questions for those who might have done this or something similar. In reading some posts it seems like many people do it in different ways and I wanted any opinions from the group.

For those who don’t know many Yanmars in the 80’s where only raw water cooled with no heat exchanger just like my model.

My plan will be to flush from either right before or right after the raw water pump, removing the impeller if I go through the pump. Does this seem correct?

I’ll be using an external pump (an AC pump that is used to flush small boilers and hot water heaters). The engine will not be hot, so I would assume I need to remove the thermostat to allow the flow to go through the block and head, past the thermostat housing, through the exhaust manifold, then through my hot water heater exchanger, exiting just before the exhaust elbow back to the supply bucket.

I will remove all the zincs before flushing and replace with new after complete.

Does it make sense to do the flow in reverse route because that would seem to have the best chance of dislodging any solids or material which may have gotten sucked into the engine and might be clogging a passages as well?

The Rydlyme will be mixed with water at a 1:1 ratio.

The engine will be flushed with clean water (possibly distilled) in the same manner when complete.

I estimate a two hour flush to be sure. Some say up to four hours for some bigger engines.

If anyone has any insights or experience with this or this particular engine it would be appreciated.

For reference, I clean the exhaust elbow every five years and it was replaced in 2013. The engine gets normally less than 150 hours per year. The exhaust manifold was also removed and cleaned in 2014, but had minimal carbon and corrosion build up in the jacket.

Thanks for your help - Neal
 

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Johnb

.
Jan 22, 2008
1,212
Hunter 37-cutter Richmond CA
Looking at what you propose it seems that you have made sure that the connection at the mixing elbow has been removed so there is absolutely no chance of water getting back through the exhaust manifold and into the engine. Good!

I once had a problem where crud clogged the outlet from the exhaust manifold right where the pipe you have labeled "thru water heater" connects. Since then I have always disconnected that pipe and eyeballed/cleaned out the outlet. Doing the flush in both directions may be a good idea. You seem to have thought out removal of thermostat and impeller well.
 

Blitz

.
Jul 10, 2007
565
Seidelmann 34 Atlantic Highlands, NJ
Looking at what you propose it seems that you have made sure that the connection at the mixing elbow has been removed so there is absolutely no chance of water getting back through the exhaust manifold and into the engine. Good!

I once had a problem where crud clogged the outlet from the exhaust manifold right where the pipe you have labeled "thru water heater" connects. Since then I have always disconnected that pipe and eyeballed/cleaned out the outlet. Doing the flush in both directions may be a good idea. You seem to have thought out removal of thermostat and impeller well.
Good to know about the water heater connection to look out for. There probably is over 10' of hose (similar to auto heater hose) going to and from the water heater, which I replaced when I pulled the exhaust manifold back in 2014. I also always wondered about any restrictions in the water heater (Raritan 6 gallon) so hopefully this process will flush that out.
 
Mar 29, 2017
475
Hunter 30t 9805 littlecreek
I had lowest drain petcock fail on removing found all kinds of sediments and sand so essentially bottom 1/3 full of trash cleaned out with wire boiler brush then back flow at that point then flow from top to float debris out. so dont just flush from one point
 

Blitz

.
Jul 10, 2007
565
Seidelmann 34 Atlantic Highlands, NJ
Whatfiero1 - do you mean the very small petcock drains on the side of the block? and that the block was 1/3 full of trash?
 
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