Thanks for all the comments. I guess no one had any information about used motor oil vs. new motor oil? Maybe that's a "rural legend" . I have used the phosphoric acid solutions and they worked pretty well, but for this car I am more concerned about internal rusting. I am not sure if it would help. I have a '73 Chev pickup that I rebuilt. I had it treated by ZBart. It seemed to do pretty well, but after several years it has dried and has started to come off ofthe under side of the truck. They had a lot of business for a while, but I think that the manufacturers started doing enought better with rustproofing that ZBart went out of business. I may put some of the Kroil in the panel and maybe some grease too.
Keep 'em running! Brady

Hey Brady, Do you think the Spray-In Bed Liner material might do what you are looking for? I've no idea if they can spray it thin enough to be practical for your need and it would probably have to be shot on "clean prepared metal".

My ZR2 4x4 is creating some stone chips along the entire bottom of the door and rocker pannel area due to the BF Goodrich ATs picking up stuff along the secondary roads I travel. When I noticed it, I got to thinking about the Spray Liner stuff and believe a 10"-12" wide band of it sprayed along the bottom side of the door pannels, rocker pannels and fenders behind the rear tires might just solve my concern.

Of course, I'd be putting it on the outside and not inside a fender well, so it would be quite simple to prep in my situation.

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Nice discussion on the "oils" everyone. I enjoyed it. Like Seafire, I'm running Mobil 1 and have been for a good number of years. Got 125K and 222K on my last two small "wanna-be" (almosta) trucks with no oil burning. (Killed both of them by hauling more than "one" grocery bag at a time in them. Won't make the Tiny Truck mistake again.)

Just heard on the news tonight that Exxon/Mobil grossed over a $Billion last year. So, either Seafire and I are buying a whole lot, or other folks are in on it too.

Synthetic oil for a guy who prefers Synthetic Stocks(me) just seems right!

Brady,

I think you could rejuvenate the rust treatment by thinning a grease with mineral spirits and spraying it in the areas you want to preserve. On a good hot day, the mineral spirits will evaporate pretty quickly and leave the grease to do the job. They make a spray for an air hose (similar to what I call a "blow gun") with a hose fitting. The hose will pick up a liquid as the air passes through the nozzle similar to a water aspirator pulling a vacuum as the water runs. You could mix as much or as little as you want at one time to spray.

Diesel oil or kerosene will take longer to evaporate.

If you thin too much, it may drip out of the rocker panel and etc.

HTH