RobWNY wrote:
I wonder if this is why oil based rust inhibitors like Krown works.
IMHO, "oil" base inhibitor work best. They all will come of over time so re-applying is required.
Thick "asphalt" inhibitors (like the old Ziebart) eventually do harden and then water can get under them and is trapped between the asphalt and the steel, allowing the corrosion to happen quicker.
Not that I do this, but probably the best way to protect the underside of a vehicle is to pressure wash it (hot water/steam even better), let dry for at least 24 hours and then spray with something like Fluid Film. Try to specifically get into "pockets"/"nooks and crannies". FF sells a kit that include a long wand so you can drill hole in the side of a door and spray in the bottom. WD40 works, but it washes off much quicker.
Small changes in the elements they mix with iron when making steel make a big difference. Better cleaning and primers also make a difference.
