An engine hoist can lift several hundred pounds by simply moving a lever. The key component of a hoist is its hydraulic cylinder, where the motion of the lifting lever is transformed by a pump into fluid pressure. Since fluid can't be compressed, the pressure causes a piston inside the cylinder to rise, which in turn lifts the arm of the hoist. The fluid is a specially formulated hydraulic oil. If the oil in the cylinder is low or contaminated, hoist movement may be erratic or inadequate.
Place old newspaper underneath the hoist cylinder to catch any lost hydraulic oil. Lower the hoist to its bottom position. Use a screwdriver to carefully pry the fill plug out of its hole in the cylinder oil reservoir. Put the fill plug in a safe place.
Use a new oil can, or thoroughly clean any old oil out of a used one. Fill the can with hydraulic oil.
Insert the spout of the oil can into the cylinder oil fill hole. Add oil to the hydraulic cylinder by squeezing the trigger on the oil can. If the cylinder is very low, or if you had to drain it for seal repair, you may have to refill your oil can several times, depending on the size of its reservoir and that of your hoist cylinder. When oil just starts to leak out of the cylinder fill hole, stop adding oil. Allow the oil to leak out until the level is even with the bottom lip of the fill hole.
Raise the hoist to its maximum height. Open the cylinder release valve, and press the hoist back down to its lowest position. This bleeds air from the hydraulic cylinder. Check the oil level again, and add more if necessary. Repeat this procedure until the lift functions properly. Reinsert the oil fill plug.
Use the rags to clean up spilt oil. Dispose of the rags and old newspaper in a fireproof receptacle.
Don't mix hydraulic oil with engine oil or other fluids. Contaminated oil can ruin your hoist.