What is a replacement for hydraulic fluid

Inquired: You ask - we answer.

In recent years, we have analyzed a large number of samples of engine and hydraulic oils from the hydraulic systems of construction machinery in our laboratory. Around the year 2000, the proportion of samples of single-grade engine oils, mostly first-fill oils, of the viscosity grades SAE 20W20 or 10W was around 50% and the proportion of approved multigrade engine oils for mobile hydraulics in the viscosity grades SAE 15W-40 and SAE 10W-40 was approx. 25%. Today, the proportion of single and multigrade engine oils in mobile hydraulics is significantly lower. Thanks to the large number of samples examined, we can make the following representative statements:

  • Multigrade engine oils SAE 10W40 and SAE 15W40 have been developed for use as engine oils. They do not behave optimally in hydraulic systems.
  • Single-grade engine oils, especially if they are designed as first-fill oils, do significantly better than multigrade engine oils.
  • HLP and HVLP hydraulic oils were originally designed for industrial hydraulics with oil change times of more than 5,000 operating hours. They can be used longer than motor oils without any problems.
  • Synthetic bio-oils based on saturated esters also behave very well, not least because of the improved oil maintenance for these expensive oils, if the residual mineral oil content of less than 2% is reached during the oil change.

These statements can be justified.

  • Multigrade engine oils tend to behave negatively in hydraulic systems. They contain an additive content of up to 25% to improve the multi-range characteristics and the engine properties. When used in hydraulics, the viscosity is initially correct, but after a relatively short operating time of often less than 100 operating hours, the VI improvers are so destroyed that the original multi-range character of the oil is no longer present. The fragments of the sheared molecules intensify the process of oil aging, cause sticky residues and impair the ability to release air. The oil can take on a black color within a short time due to the "diesel effect". There is a risk of damage from cavitation.

Comprehensive information on the problem of "black oil and diesel effect" can be found in ?????? ÖlChecker Spring 2000.

  • Single-grade engine oils behave similarly to detergent HLPD hydraulic oils. They contain an additive package developed for motor oils. The high proportion of cleaning and dirt-carrying agents is not required for hydraulics. These oils become problematic because the additives impair the air release behavior after a short time so that the risk of cavitation damage increases considerably and sealing problems are increased by the diesel effect.
  • HLP industrial hydraulic oils are designed for long-term use in hydraulics. They contain exactly the right base oil and one selected for use in hydraulic systemsAdditives. However, it should be noted that there are basically two types of hydraulic oils, namely zinc-containing and zinc-free. Strict care should be taken not to mix these two types. Mixtures can lead to sludge-like precipitations of the zinc-containing reaction products and clog filters or are the cause of cavitation, as the air separation capacity can be severely impaired. Furthermore, a mixture of zinc-containing and zinc-free hydraulic oil can lead to strong foaming.
  • Bio-hydraulic oils based on saturated esters show just as good performance in construction machinery. Due to a natural EP behavior, only a few additives (mostly based on sulfur-phosphorus) are required. Due to the polar properties, there is less stick-slip (stick-slip effect) and squeaking. The sealing and guide rings in cylinders remain elastic longer. Due to the finer filtration, which is shown in a better purity class, and the greater care required because bio-oils are relatively expensive, they can often be used for up to 10,000 operating hours as a lifetime filling.

However, which type of oil you choose in the long term, please be sure to observe the instructions of the system manufacturer during the guarantee period and use the analyzes to check whether the oil you have planned is actually still being used!

Also read: Miraculous oil multiplication in the engine of a construction machine