Citric acid in block

[philthehill]

I have just opened up the 948cc block which has had the water gallery soaking for at least 4 weeks with citric acid.

The citric acid has got rid of the rust but appears to have formed salt crystals on the walls of the water gallery. The other 948cc block which had the same diluted citric acid mixture at 6 tablespoons per ltr of hot water was free from any salt crystals and was perfectly clean once flushed through.
I have now reduced the diluted mixture to 4 desert spoons per ltr of hot water and refilled the block. I will see if the weaker mixture reduces or eliminates the forming of citric acid crystals.
It is strange that one block was perfect and the other has formed salt crystals

[Biggles1957]

I would have thought that flushing it through will just dissolve any acid residue now?

[philthehill]

I have flushed the block thoroughly and it has not got rid of the salts.
I am hoping that the weaker solution will eat the salts away.

[Biggles1957]

Hmmm - that's interesting that plain water hasn't dissolved it? Citric acid dissolves pretty well in water usually - have you tried pouring boiling water on the bits you can see?

[Murrayminor]

I wonder if it reacted with any previous anti freeze.

[Biggles1957]

Well I thought there must be some sort of reaction going on, but I think he flushed it all out first before putting the citric acid in? Concentration of that isn't critical at all - even quite concentrated won't hurt the iron - just dissolve the iron oxide. It doesn't make sense that the crystals he's now left with don't want to dissolve if they really are citric acid that has crystallised. I would pour boiling (as hot as practicable at any rate) water on and see if they dissolve then.

[les]

I’m getting ready to clean the waterways in a cylinder block, with some citric acid. I’ve bought new core plugs but on reflection I’m thinking why disturb the old ones if they don’t leak. Is leaving them alone a reasonable decision?

[philthehill]

Les
Personally I would use the citric acid with the old core plugs in place. When you are happy with the result - flush and replace the core plugs.
You never know what the internal surface of the core plug is like. The citric acid may have made the core plug paper thin from the inside even though the outside looks good.

As regards the block with the salts - it has been put in a corner with a fresh lot of citric acid and will be left until required as it is a no rush job.

[les]

Thanks Phil. Yes that makes perfect sense. I think I’d always be wondering what was lurking behind the plugs and I hadn’t considered the erosion aspect. Decision made !
Will your block be ok if acid is left too long, or does it reach a point where it is inactive?

[les]

Citric acid now in block, it took just under 1,5 litres and 9 desert spoons. I’ll leave it in for a few days.

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[JOWETTJAVELIN]

I have just filled up a 948 block with the solution, and did it last year on a 3 litre Humber block to great effect. What I drained off came out black, and it took a few weeks driving the car with plain water, draining and filling with plain water again, before it came out clear. So it definitely works and is a good tip from Phil.

I am thinking crystals might be formed depending on the hardness of the water you use - fortunately I live in a soft water area which is great for cooling systems, and cups of tea!

[JOWETTJAVELIN]

So it's been about a month now and I drained the block.







Engine soup.