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Chemical cleaning a dark deposit from surface of aluminium engine block casting

We have a number of engine blocks that need to be cleaned to remove a dark grey deposit from the cast surface.

We have tried 20% Nitric acid, 10% phosphoric acid, petroleum spirit, and toluol with limited success. The deposit could be a burnt on die lubricant as it feels a little greasy.

I need to organise the treatment of over 100 engine blocks to remove this stain but am at a loss as to what will work without attacking the cast iron cylinder sleeves.

Can you help

Graham Dodd
Automotive - Melbourne Victoria Australia
2005

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Hello Mr Graham;

Use your nitric acid cocktail after swaying your blocks around in a solution of 50 - 100 gms per litre of Sodium Hydroxide for 20-60 seconds first and rinsing afterwards. This won't affect your steel Liners but will effectively etch the aluminium first.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2005