Oxalic acid to unblock outboard waterways?

westhinder

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My 3.3 hp 2-stroke Mercury outboard has a restricted water flow. The cooling water has become a dribble instead of a healthy pee.
Can I use oxalic acid to flush the waterways? That is the acid I have available right now.
 

rbmatthews

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For our Tohatsu 3.5, I find that poking a straightened paper clip up the tell-tale clears any salt deposits etc. about 80% of the time. The other 20% I have used fairly hot water pushed through the system in reverse using a gravity feed attached to the tell-tale. A bit Heath Robinson, but it seems to work, and no need so far to resort to acids. Giving it a thorough flush out at the end of the season with fresh water also helps.
 

VicS

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My 3.3 hp 2-stroke Mercury outboard has a restricted water flow. The cooling water has become a dribble instead of a healthy pee.
Can I use oxalic acid to flush the waterways? That is the acid I have available right now.

The pee is just a tell tale that tells you if the pump is pumping OK. Check and unblock that first.

You may still need to flush the water ways if its not cooling properly.

Oxalic acid would not be my first choice

A domestic or central heating descaler would be better IMO. Fernox DS 3 is a powerful descaler based on sulphamic acid, which is a much stronger acid than oxalic.

http://www.fernox.com/products/water+treatment+chemicals/limescale+remedies/limescale+remover+ds-3
 

William_H

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West Australia
My 3.3 hp 2-stroke Mercury outboard has a restricted water flow. The cooling water has become a dribble instead of a healthy pee.
Can I use oxalic acid to flush the waterways? That is the acid I have available right now.

Do you mean that just the tell tale is dribbling or is the motor when running showing signs of overheat with lots of steam in the exhaust. If it is overheating then it is not likely to be the tell tale blocked but rather a pump failure or general cooling water blockage. So in my experience (witha Johnson) pull the pump and check that. good luck olewill
 

VicS

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Do you mean that just the tell tale is dribbling or is the motor when running showing signs of overheat with lots of steam in the exhaust. If it is overheating then it is not likely to be the tell tale blocked but rather a pump failure or general cooling water blockage. So in my experience (witha Johnson) pull the pump and check that. good luck olewill
 

westhinder

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Do you mean that just the tell tale is dribbling or is the motor when running showing signs of overheat with lots of steam in the exhaust. If it is overheating then it is not likely to be the tell tale blocked but rather a pump failure or general cooling water blockage. So in my experience (witha Johnson) pull the pump and check that. good luck olewill
No signs of overheating. The pump and impeller seem to be ok. I let it run in a tub of water for over an hour. That improved the dribble from the tell tale, but didn't bring it back to what I expected as normal. That's why I suspect a buildup of scale in the cooling channels, which I want to clear before it gets worse
 

VicS

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No signs of overheating. The pump and impeller seem to be ok. I let it run in a tub of water for over an hour. That improved the dribble from the tell tale, but didn't bring it back to what I expected as normal. That's why I suspect a buildup of scale in the cooling channels, which I want to clear before it gets worse

I take it then that you have inspected the pump and impeller.

Have you actually made sure the tell tale is clear, right back to the connection on the engine
 

aquaplane

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West Yorkshire
I have used Oxalic acid on my old Volvo but that is cast iron and it did no discernible harm and actually improved flow.

I would be more careful with aluminium engine but a weakish solution for a reasonable time should be OK. Don't boil it overnight to give it a good seeing to.

Sulphamic acid may be more effective but not if you don't have any.
 
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