Can you identify the brand and type of the hoist? if it is a single cylinder (sounds like it is) and it lies horizontally when lowered it would be a twin arm underbody. All of them from the 30's onward used cast itron piston rings and were of low pressure design (1000 psi rated) and gear pumps which is why they would work with heavy weight oil but were not originally intended to. Hydraulic oil from that era was generally 5W and if it's heavier then someone unwitingly likely used motor oil in it. Not good but won't hurt it.
First thing is to check for air being pulled in thru a fitting or around the pump or cylinder. Trapped air will blow oil out at the smallest leak or largest leak whichever is closest to the compressed air. Oil returned to the reservoir will be foamy too. If it will hold in the raised position overnight then you can probably eliminate the broken piston ring possibility. Also check for leaking at the cylinder rod area. If thats a leak then it requires the rod packing to be replaced. It's simply a matter of elinination to locate the problem area. If the cylinder requires rebuilding and your not comfortable removing it from the hoist frame then by all means take it to a good equipment repair facility. Don't risk your life working under a raised body. If the cylinder head is welded on then you must have it machined off and rewelded.
Last edited by 53moneypit; 11/10/2012 11:15 AM.
