Hydraulics is a drive technology that uses fluid under pressure. This fluid is usually oil.
Oil viscosity is important. Hydraulic oil used for tail lifts has a high viscosity index. The viscosity index tells you how thick the oil is at different temperatures. The thickness of oil with a high viscosity index changes less with temperature fluctuations.
It is important to use oil with the right viscosity. Oil that is too thick will make the tail lift respond slowly. The tail lift will be starved for oil, because the pump has difficulty picking up the oil. Oil that is too thin causes wear, because the system ‘runs dry’.