Outboard engine descaler

VicS said:
£9.95 per litre
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I guess say 10 ltrs would be enough to run the engine in a bucket. So how many litres of Rydlyme would I need for that, it is used neat or mixed with water?
 
VicS said:
Vinegar is a dilute solution ( about 5%) of a fairly weak acid, acetic acid, pKa = 4.76.

Safe? certainly. Safest? possibly.

Most effective? Hardly! 1 litre of 5% acetic acid will dissolve , in theory, only 41.7 g of calcium carbonate scale and it will do so rather slowly compared with an equivalent concentration of a strong acid such as hydrochloric acid.

Cheapest ? Possibly even at around 50p per pint from supermarket
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So is acetic acid available in powder form that can be mixed up to a stronger concentration? If so what quantity should I use per litre of water.
 
NickC said:
So is acetic acid available in powder form that can be mixed up to a stronger concentration? If so what quantity should I use per litre of water.
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Well whatever it is I mix one sachet with about 1/2 litre boiling water so the last just dissolves. Doesn't hurt the skin like hydrochloric, and two soaks shifts most stuff, and the gas released isn't too pungent either. Also seems to ignore most metals, and doesn't dezincify brass (turn it from yellow to red). I do remove any zinc anodes first.
 
penfold said:
Citric acid is cheap to get in bulk.
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Good suggestion, it is beginning to look like citric acid might be better than vinegar. Any idea what concentration should be mixed up for this cleaning purpose?

I can get 1Kg for £6 so it is certainly cheap enough.

Some concern about whether Citric acid is strong enough to do the job as Sulphamic acid is another suggestion that I have read about.

Edit:
Sulphamic acid also available for £10 per Kg. So which is likely to be best Citric acid or Sulphamic acid?
 
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NickC said:
I guess say 10 ltrs would be enough to run the engine in a bucket. So how many litres of Rydlyme would I need for that, it is used neat or mixed with water?
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It used to be possible to find instructions for using Rydlyme for descaling outboards. Essentially running the engine in a small tank of diluted Rydlyme. Pretty much as Pampas describes in #7

I cannot find them now. I am wondering if it is no longer recommended for outboards.

Acetic acid is not available in powder form . Pure acetic acid is a liquid which, due to the pungent fumes, is rather unpleasant to handle.

Actually when 100% pure it freezes at 16C. In reality even laboratory grades are not quite 100% so normally freezes somewhat lower. I have only ever seen it solid once.

Fernox DS-40 is a citric acid based central heating cleaner and descaler. It contains an indicator so it is possible judge when all consumed and enable more to be added.

Fernox DS-3 is a more potent general and boiler descaler based on sulphamic acid. Sulphamic acid is one of the strongest of the weak acids with a pKa of 1.0


( citric acid is stronger than acetic acid with a pKa1 of 3.13 )

I have seen phosphoric acid suggested for descaling. It has a pKa1of 2.15 so is in fact a weaker acid than sulphamic acid.
 
After much head scratching I think I am going to try out Sulphamic acid. Available from ebay at £11 for 1Kg which I hope will provide enough to mix with 10ltr water. Also hope that 10ltr water is enough in the bucket to run the engine in.

If anyone knows any cheaper suppliers for this please let me know.

Thanks for all the advice, will report back later on whether this was successful or not.

Nick
 
Hi John,

Interesting but I am based in the UK so posting it from NZ might unfortunately cost more than buying it from a supplier in the UK. Looking at the recommended concentration for Fernox DS-3 which is Sulphamic acid based it seems 100mg per litre is recommended.

Nick
 
NickC said:
Hi John,

Interesting but I am based in the UK so posting it from NZ might unfortunately cost more than buying it from a supplier in the UK. Looking at the recommended concentration for Fernox DS-3 which is Sulphamic acid based it seems 100mg per litre is recommended.

Nick
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A lot of the supermarket descalers are sulphamic acid based, I think the one that lives in our bathroom is called vical or something like that.
 
I've never descaled an outboard in my puff.
Is it really that necessary? Present main outboard spends most of its life on a mooring, nine years old and still on its original water pump impeller. Lots to give me sleepless nights, without adding the possibility of waterway salt deposits to the list :)
 
On a previous post I mention that I series up the s/w systems on the main and aux engines 1 Ltr did both in about 1/2 gallon of fresh water.
Don't care what's in it except that it does what it says on the can, those who have never used it should try some, it really works and its easy to tell when its "Spent", also no need to flush out,leave it there until you next start the engine on sea water.
 
Just reporting back:
Engine flushed over the weekend with that sulphamic acid. Took about 3-5 hrs of flushing / resting cycle as water indicator jet very gradually got slightly stronger and stronger. Unfortunately had to use a lot more water than expected so concentration was probably only half what I was aiming for but still seemed to work.

Took her out for a test run on the river on a small rib yesterday and had a very constant, reasonable but not heavy, flow from the indicator for all that time. I guess this is probably about as good as this engine is going to get.
 
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