Making some "free" stuff to use in a pinch is not the same as making it for routine regular use. Calculate the cost to make a full gallon and then let's see where you are. There are plenty of good "natural" rust solutions on the market. The one I use is $20/gallon for a concentrate that will yeild 4 gallons when mixed. At that price is it really worth all the farting around? That's time you could have been working on your car or spending with your kids.