Gibbs won this round. It reached the Plexiglas plate within about five minutes
of the pin being stood in the fluid, matched only by diesel fuel, then climbed
an inch and a half over 24 hours and worked roughly a quarter of an inch into
rusted threads from below. On the lug nuts — half-inch wheel studs torqued to
80 ft-lb and chemically rusted over several weeks — a single application given
one hour to work left the clearest visible penetration at both ends of the nut
of anything tested. Free All finished second and Mouse Milk third, and the
three are close enough that the gap between them is smaller than the gap
between any of them and doing nothing.
On price the 3-in-1 is the pick. It is the cheapest fluid here at $8.29 and the
cheapest by volume at $1.04 an ounce, and it was the thickest of the group,
coating the entire nut and bolt instead of running off. It climbed the least of
the four oils up the pin at about an inch and an eighth, but once it reached
the threads it worked at least a quarter of an inch up them, as far as the
winner did. Free All sits just above it at $11.93, or $1.10 an ounce, with a
slightly stronger showing on the lug nuts. Gibbs is the most expensive product
here at $44.95, though at $1.25 an ounce it is not far off the rest.
Two cautions are worth carrying into a purchase. The claim that plain water
frees rusty fasteners as well as a penetrating oil does not hold up: water
moved about a quarter of an inch up the pin in 24 hours, never reached the
plate, and after an hour on a rusted lug nut looked exactly like the untreated
control. Diesel fuel is the more interesting case, because it climbed further
than every oil and did work about a quarter of an inch into the threads, yet on
the one-hour soak it left an oily film and nothing more. Creeping up a surface
and penetrating rusted threads are different jobs, and a fluid that is good at
the first is not automatically good at the second. Time is the other variable:
every product did far more over 24 hours than it managed in one, so leaving a
seized fastener to soak overnight is worth more than the choice between these
brands.