Hidiy deant54-
Is this "under coating" on your truck the commercially available chassis under coating similar to a line-x or Rust-Oleum product? Or is your "under coating" grease/oil/grime/engine residue? I understand your question, but I'm getting confused because I've heard the term used interchangeably.
A better way to ask: did somebody put it there on purpose, or is it 60 years of accumulated Stovebolt funk?
Either way, I would sandblast it off if I got to pick any method of removal. Glass beads as the blast media.
I'm right in the middle of cleaning up my 55.2 3100 frame, but I don't have the blasted media option. So, here's what all I've used (my enemy is 60 years of Stovebolt funk): pressure washer, strong laundry detergent, scrub brushes, a good USA-made paint scraper tool, various wire brushes, rifle chamber brushes, tooth brushes, Purple Power degreaser, more hose pipe water, baby bottle brushes, dish brushes, a wire cup brush on an angle grinder, and more spray degreaser... Rinsed, and repeated several times.
A big jar full of elbow grease probably helped the most.
If your hood is installed on your truck, and there's an engine still installed under it, use some caution as to what all you use chemical-wise. I have not tried my cleaning method on an assembled truck, but the principle is the same.
Hope this helps & have fun!
Brad
