Can hydraulic oil be used in the steering gear?
4 Answers
Hydraulic oil cannot be used in the steering gear because the viscosity of hydraulic oil is different from that of power steering fluid, and mixing them will affect the normal operation of the steering gear. Hydraulic oil is a hydraulic medium used in hydraulic systems that utilize liquid pressure energy, playing roles in energy transmission, wear resistance, system lubrication, corrosion prevention, rust prevention, and cooling. Symptoms of steering gear failure include: 1. Difficulty in returning the steering wheel to its original position; 2. Steering wheel shaking or vehicle pulling to one side; 3. Uneven steering effort (heavy on one side, light on the other); 4. Steering gear oil leakage; 5. Abnormal noises from the steering gear. The function of the steering gear is to amplify the force transmitted from the steering wheel to the steering linkage and to change the direction of force transmission.
Last time I serviced my old Jetta, the mechanic specifically warned me about this issue. Hydraulic oil should never be randomly added to the steering gear, as it requires specialized power steering fluid. These two have different viscosities and additive compositions. Mixing them can corrode the steering gear's sealing rings, leading to oil leaks at best, or heavier steering and even failure at worst. My car suffered from this - after hydraulic oil seeped in, the steering gear's dust boot bulged, and the repair cost me nearly a thousand yuan. For oil changes, it's best to let professional shops handle it; the original oil containers they use are marked with a letter 'P' at the beginning.
I've modified the steering systems of over a dozen cars, and putting hydraulic fluid in the steering gear is a big no-no. While automatic transmission fluid is also a type of hydraulic oil, its high-temperature shear resistance index falls far short of the standards required for steering gears. The steering gear has to withstand pressures up to 250 bar during turns, and ordinary hydraulic fluid will foam under high temperatures, causing the pump to whine loudly after steering. The biggest issue lies with the rubber seals—zinc elements in hydraulic oil can cause the nitrile rubber rings inside the steering gear to swell, leading to oil leaks within six months. Just last week, I repaired a Civic where the owner had used the wrong fluid, causing all the oil seals to swell up.
Running an auto repair shop for twenty years, I've seen countless cases of wrong oil usage. Hydraulic oil and power steering fluid are like diesel and gasoline—they may look similar but are worlds apart. Power steering fluid needs to lubricate gears while providing hydraulic assistance, with 30% higher fluidity than regular hydraulic oil and double the antioxidant content. One customer added forklift hydraulic oil to their power steering system, resulting in steering that felt like moving bricks in winter. An even worse case saw the pump bearings develop grooves in just three days after mixing oils, costing over 8,000 yuan to replace the entire assembly. The safest bet is to look for the steering wheel symbol on the power steering reservoir cap.
