Freeze plug problems

[John Brown]

Oxalic acid https://en.wikipedia.org/wiki/Oxalic_acid was the main ingredient in the old chemical flush that came in a two part can from your local auto parts store or dealership parts department, that came with a neutralizer in the lower half of the can.

Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent). Its utility in rust removal agents is due to its forming a stable, water-soluble salt with ferric iron, ferrioxalate ion.