Motul Motorcycle 10W-30 is the pick for wear protection: the smallest wear
scar of the six at 5.47 mm, the second-lowest evaporative loss at 2.62 g, a
2,052 ppm anti-wear package on a strong base oil, and the quietest run on the
lubricity rig. It costs $53 per gallon and it was the slowest 10W-30 in the
cold at 2 minutes 37 seconds, so it earns its place in a warm engine rather
than a winter one. Motorcraft Diesel Engine 10W-30 finishes a very close
second at 5.57 mm for $32, adds the most stable behaviour after heat - only 8%
slower to flow once cooked - and is the value pick of the group, with the
caveat that its high phosphorus content is the reason it is not recommended
for gasoline engines running a catalyst.
Each of the others wins something specific. Mobil 1 0W-8 owns the cold: 15.5
seconds down the -40°F track against 71 for the 10W-30 and 202 for the
aviation oil, and $28 covers five quarts. Phillips 66 20W-50 Aviation Oil
resists heat better than anything else here at 2.39 g of evaporative loss.
Quicksilver 10W-30 Marine Oil is the quiet all-rounder, with a 5.98 mm wear
scar that beats both gasoline-engine oils, 5.25 g of evaporative loss and only
a 13% cold-flow penalty after the heat. Mobil 1 10W-30 is the fastest-flowing
10W-30 when warm at 1.58 seconds and holds evaporation to 5.26 g.
Two findings are worth carrying into a buying decision. First, a big additive
package does not substitute for film thickness: Mobil 1 0W-8 has roughly twice
the anti-wear content of the 10W-30 and still produced the largest wear scar
in the comparison at 6.56 mm, so an engine specified for 0W-8 wants 0W-8 and
nothing thicker or thinner. Second, oils formulated for a specific machine
behave that way in every direction. The aviation oil's total base number is
0.6 against roughly 6.9 to 7.8 for the rest, and it carries only trace levels
of the detergents and dispersants that keep a road engine clean, while the
diesel, motorcycle and marine oils all carry far more of them than the oil
made for cars. Matching the oil to the engine matters more than picking a
brand.