CrimsonLake.. first you don't say what type of hoist it is, underbody (most likely) or telescopic. That would indicate whether it has a reservoir or is a totally closed system. If it is an underbody twin arm them Jerry is correct about the cylinder containing the oil and the proper filling method. What I used to do on all the S/A undersbodies in my shop was to drill a hole across the square part of the pipe plug and then drill upward from the bottom to intersect to other hole. About a 3/16 hole and then put an 1/8 cotter key threw it. This allowed air to escape as it was cycled a few times w/o allowing a quart of oil all over the place. This apploes to single acting (S/A) models only. If D/A then don't use the plug trick. Also use standard hydraulic oil, 30W is too heavy for the old gear pump and newer oils have too much detergent in them for any old system thats full of crap. I really doubt that your problem has anything to do with pressure or it wouldn't lift the body off the frame. The twin arm underbodies will continue to lift any load it can start as that is where the torque requirments are the highest. It actually becomes easier to lift the further up it goes. When full of oil the hoist will simply bypass at the end of it's stroke and continue to hold or you can place the valve in the center hold position. If you can give me the brand and model number of your hoist I may have a lot more info for you.
