600wt Oil
Many oil companies define 600W cylinder oil as "for use in splash-lubricated enclosed worm gearsets operating at moderate to high speeds and temperatures. It also is recommended for lubricating steam cylinders, couplings, bearings, and the break-in of compressor cylinders".

Oil called 600wt can be confusing, the 600 is not the viscosity but rather flash point. Also known as Steam Cylinder Oil, it was common in the early part of the 20th century and used extensively by the railroad because of it's heat tolerance. Several oil refiners have a form of this oil, but you have to get it from a jobber. The factory calls for its use in the steering box, transmission, spring shackles and rear-end. Here are some sources:

Most Model A & T Ford suppliers

Restoration Supply Company
15182B Highland Valley Rd, Escondido, CA 92025
(800) 306-7008 Phone
(760) 739-8843 FAX

Torco Oils
PART # A-T250W
Piranio's Antique Auto
102 N. Ohio, Celina, Texas 75009
(972) 382-2742 Phone
(972) 382-2542 FAX

Available for Jobber in 5 gallons pails

Meropa 680
Product code is: 02342

Mobil Oil
600W Steam Cylinder Oil
600W Super Steam Cylinder Oil

Shell Oil