[Old Henry]

After seeing the vinegar fail to finish the job of eating away the rust I continued pondering why it failed and finally had the thought that maybe it had lost its acidity so I dropped a pinch of baking soda into it which should have caused the usual chemical reaction. Nothing. Three pints of vinegar were neutralized by just the intake of the water pump sitting in it for several days before it even finished the job it started. Pretty poor performance in my opinion. Doesn't really predict great success in an engine block where the ratio of rusted metal to vinegar is way higher than my test was.