I have never had satisfactory results using Naval Jelly. The metal prep and rust remover that I use is actually a liquid. It almost looks like a cross between antifreeze and windshield washer fluid, in its color. It has been very useful on everything I have used it on. If you have a part that looks like it is totally bad because of rust, I have found that if done carefully, it will remove all of the rust, but it will leave the factory paint intact. It seems like the product could be used for about 4 different degrees of rust removal.
1. It will remove all surface rust with just a short time soak, then rinsed.
2. It will remove all surface rust and all paint, and leave a fresh bare metal finish, then rinse.
3. A prepped steel body panel, can be sprayed with the product, then left to dry. It will then have a protective coating, which looks almost like you have sprayed a clear coat finish on to the body panel. This is great for fairly long term storage to prevent rust while being stored and waiting for assembly and paint prep. EXCELLENT!!!!
4. You can actually dip steel body panels, trunk lids, tailgates, etc. and let the item dry, then dip again, let dry then dip again, etc. It will produce a parkerized like finish. See:
http://en.wikipedia.org/wiki/Parkerize
This product that I use, originally came from the oil patch, being used on off shore oil drilling platforms. It is applied and let to dry, then painted over, to protect the metal on the rigs. i have been using this product for many years now, and I really don't know what I would do without it anymore, it is just to easy to use, and has so many ways it can be used. the down sides that I have found are very few:
1. Use on ferrous metals only.
2. Do not use on galvanized, chrome plated, or pot metal items.
I have made several, specialized dipping/soaking tanks, for various applications of different sized parts. One other neat feature of this product is that after you use it to clean up your parts, it can be recycled for further use at another time, by running it through a coffee filter to remove the sediment. I have some of it that I know is at least 5 or 6 years old, it still works great. It is an item that I have come to be dependent on in my shop. It just works sooo good!