How much oil should be added to a jack?
3 Answers
Fill it to four-fifths of the oil reservoir. Considerations for selecting hydraulic oil: 1. Appropriate viscosity: Viscosity is the primary factor when choosing hydraulic oil. At the same working pressure, if the viscosity is too high, the movement resistance of hydraulic components increases, temperature rises faster, the self-priming capacity of the hydraulic pump decreases, and pipeline pressure drop and power loss increase. If the viscosity is too low, it will increase the volumetric loss of the hydraulic pump, increase internal leakage in components, and thin the oil film on sliding parts, reducing their load-bearing capacity. 2. Lubricity (anti-wear properties): Hydraulic systems have numerous moving parts that require lubrication to prevent wear on relative moving surfaces, especially in high-pressure systems where the anti-wear requirements for hydraulic oil are very high. 3. Oxidation resistance: Hydraulic oil oxidizes during use. The acidic substances produced after oxidation increase metal corrosion, and the sludge deposits formed can clog filters and small gaps, causing the hydraulic system to malfunction. Therefore, good oxidation resistance is required.
As a user of an older model hydraulic jack, I mainly add oil through the oil filler hole at the top. Typically, filling it to about 5mm below the filler hole is ideal, ensuring proper hydraulic system operation without overflow. Remember to use dedicated hydraulic oil or No. 10 engine oil—avoid substitutes like cooking oil. During my last maintenance, I noticed that insufficient oil prevents the jack from lifting, while overfilling causes leaks through the seals. A quick tip: always check oil levels and for leaks before each use—safety comes first. For long-term storage, retract the piston to its lowest position to prevent seal deterioration.
As a mechanic with ten years of experience, when dealing with jack oil refilling issues, I first check the oil window position. For models with an observation window, filling to the middle mark is sufficient; for those without, fill until the oil level is 3-5 mm below the port opening. The key is to use the correct oil—preferably ISO VG32-grade hydraulic oil, though 10W engine oil can be substituted in emergencies. Always clean the filling port thoroughly before adding oil to prevent debris from entering and clogging the oil passages. Additionally, after refilling, pump the handle several times to purge air from the system—success is confirmed when no hissing sound is heard from the hydraulic cylinder. For jacks left unused for extended periods, it's advisable to check the oil condition every three months.
