Descaling outboard and (raw water cooled) main engines

PowerSlapper

PowerSlapper

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Does anyone have actual experience of using Sodium Hypochlorite solution for cleaning out the waterways on small outboards (aluminum waterways) and/or raw water cooled mains (cast iron blocks). This method has been "recommended" to me however i am a little dubious of running bleach through the engines to remove the salt deposits.
 
I have a Honda 2.3 outboard and works well. However, whilst it is air cooled there is an exhaust leg and currently water is dripping very severely from the underside of the cowling at the top of the leg. Could the exhaust require de scaling of could it be blocked in another way. Any advice very welcome.
I agree with Citric acid-I have a Bukh DV 20 and Bukh Poole recommended the use of Citric acid to clear the manifold channels.
 
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PowerSlapper said:
Does anyone have actual experience of using Sodium Hypochlorite solution for cleaning out the waterways on small outboards (aluminum waterways) and/or raw water cooled mains (cast iron blocks). This method has been "recommended" to me however i am a little dubious of running bleach through the engines to remove the salt deposits.
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I do not think it would do any good at all but if the person who recommended it cares to explain the chemistry involved I'll think again.
 
singlehanded said:
I have a Honda 2.3 outboard and works well. However, whilst it is air cooled there is an exhaust leg and currently water is dripping very severely from the underside of the cowling at the top of the leg. Could the exhaust require de scaling of could it be blocked in another way. Any advice very welcome.
I agree with Citric acid-I have a Bukh DV 20 and Bukh Poole recommended the use of Citric acid to clear the manifold channels.
Click to expand...

Hi you have a large rubber bung with holes for the driveshaft and exhaust pipe to pass through on your honda 2.3. This is primarily for sound deadening but does stop a lot of water entering the leg. The exhaust has relief holes near the manifold and i have never seen one blocked. The only corrosion I see on the leg is underneath the square plastic cover. The stainless exhaust against zinc coupled with moisture from the inspection hole does cause corrosion.
 
I dose my raw water cooled Volvo Penta 2003 with about 10% Hydrochloric acid, about once a year. Of course, I take the engine anode out first! That works very well, and when I refit the engine anode (which drains the block) it is surprising how much black scale comes out - this after running the engine for a few minutes to clear the acid out. Seems very effective; HCL does an excellent job of removing scale build up, and is harmless for short exposures to both cast Iron and Aluminium (I wouldn't leave it for too long; half an hour seems to be long enough). I get my HCl from the laboratory where my wife works, but it is readily available as brick cleaner elsewhere.

Any weak acid such as Citric or Sulphamic acid would probably work, but note that not all citrates are very soluble. HCl has the great advantage that the only common(ish!) insoluble chloride is silver chloride, which you're unlikely to encounter in an engine. Nitric acid would be even better at removing scale - there are no common insoluble nitrates - but as it is also a strong oxidizing agent, I'd be concerned at the potential for it attacking the metal of the block.
 
I used Rydlyme on my 2GM20, cracking results.

Thermostat before:
qD0EJf0l.jpg


Thermostat after, next to the one I purchased as I thought the old one was past it!:
FVod2Wdl.jpg


Process looked a bit like this, pumping the solution through with a little £12 12V pump from ebay.
qoPXVW4l.jpg


Diagram here:
sSiSiNtl.jpg


Let me know if you want details...
 
Only today someone was saying they cleared gunge from a small outboard's cooling system with a wallpaper stripper and attaching a small hose. I pass this on without personal knowledge of the process.
 
dgadee said:
Only today someone was saying they cleared gunge from a small outboard's cooling system with a wallpaper stripper and attaching a small hose. I pass this on without personal knowledge of the process.
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Humm. That would be steam, the usual product from a wallpaper stripper. Also what will be produced by a blocked up outboard cooling system...
 
steve66 said:
Hi you have a large rubber bung with holes for the driveshaft and exhaust pipe to pass through on your honda 2.3. This is primarily for sound deadening but does stop a lot of water entering the leg. The exhaust has relief holes near the manifold and i have never seen one blocked. The only corrosion I see on the leg is underneath the square plastic cover. The stainless exhaust against zinc coupled with moisture from the inspection hole does cause corrosion.
Click to expand...
 
Hi Steve, many thanks for your response. I will be taking it apart again tomorrow so will have a look. From memory last time the exhaust is held in place by two bolts at the top but does not pass through a rubber bung. The drive shaft just slots in to a cog at the bottom of the clutch housing. I should add this is a 2015 model.
Regards
 
singlehanded said:
Hi Steve, many thanks for your response. I will be taking it apart again tomorrow so will have a look. From memory last time the exhaust is held in place by two bolts at the top but does not pass through a rubber bung. The drive shaft just slots in to a cog at the bottom of the clutch housing. I should add this is a 2015 model.
Regards
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Hi Word of warning.. Dont try to unbolt the exhaust unless you absolutely have to. Trust me there is a big rubber bung in the outboard leg that the driveshaft and exhaust pass through. The current 2.3 model mechanically has not changed since 1998
 
Good morning Steve I have already had to remove the exhaust in order to access the clutch as it has seized due to a dunking. That problem is resolved but I just have this water dripping to cure now!! I wonder where in the leg is the bung positioned in order to gain access to it?
 
singlehanded said:
Good morning Steve I have already had to remove the exhaust in order to access the clutch as it has seized due to a dunking. That problem is resolved but I just have this water dripping to cure now!! I wonder where in the leg is the bung positioned in order to gain access to it?
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Hi . The bung is at the bottom of the leg near the cavitation plate
 
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