SteveB wrote:

I got an old hydraulic jack. It is 10" high, 4.5" diameter, with a 2"
piston. It is obvious that it has sat for a long time. It had some mud on
the outside. Jack oil runs out the fill plug, and when I remove the turn
screw, jack oil comes out the bottom. The pump pumps out the piston, but
only a short way, then the pump becomes easy, leading me to believe it is
low on oil. BTW, how much oil do I put in there? Up to the fill hole?

Should I just put some jack oil in there, or is there a process to flush,
which may take out any water in there? Would some Marvel Mystery Oil harm
the seals? Would there be another fluid to flush it with? Or should I just
fill it with oil and call it good?

This appears to be an older one, not Chinese. Are these rebuildable? Out
scrounging for cribbing for a new container, and found a volume tank for a
compressor, too. Think I'll make a portable air tank out of that.

I love to go scrounging. Took my 86 yr. FIL, and he's just a big kid when
it comes to puttering and scrounging.

Steve

Low on oil most likely. Take it apart, clean in suitable solvent, then
reassemble and fill with fresh jack oil. Any hydraulic shop should be
able to find suitable seals if needed.