I rented a hot-water (190 degree) pressure sprayer (True Value Hardware) to clean up to 3" of caked grease/dirt from the frame of my 54/55 GMC 2-ton COE flatbed (about an 18" platform over the long frame).
That nicely took the frame down to tight-paint/metal. The frame had lived all its life on the "high desert" apple growing area of Washington state.
After it dried, the whole frame was quickly/roughly wire-brushed, and then painted with POR-15, and then painted with two coats of POR black semi-gloss finish coat (roller & brush painted).
It looks good (I am regularly asked if I took the frame down to bare metal).
