Biodegradable hydraulic oil is used so as not to pollute the environment in the event of leaks. However, these synthetic esters are highly hygroscopic and decompose on contact with water (hydrolysis).
When operating a snow groomer in a ski resort, the temperature is below 0°C. Whereas in the engine compartment, an elevated temperature of 20°C, for example, prevails. At an average humidity of 50% RH, the air thus binds 8.6g of water per 1m³ of air. If the air is sucked into the tank, the moisture will remain there. If the hydraulic tank cools down to the ambient temperature at the end of work (critical from below 9.2°C), the humidity in the tank will condense. This means that the risk of condensation water damage in a snow groomer is very high.