Changes in oil pressure of the hydraulic control panel at natural gas wellheads due to temperature effects – Urgent assistance needed

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Recently, we encountered an issue at one of our natural gas wellheads where the shutdown was caused by excessive hydraulic oil pressure in the control panel. During the analysis of the causes, there was one issue that wasn’t fully understood, and I would like to seek advice from those with relevant experience. As a result: The pressure of the hydraulic oil in the wellhead safety valve control panel is affected by temperature, rising from around 55 MPa to 58 MPa; this causes the hydraulic oil safety valve to activate, and the oil pressure drops rapidly to the interlock value of 41 MPa, leading to the shutdown of the well. The oil pressure is controlled such that the piston pump starts automatically when it falls below the set value (mechanical control), and it stops operating when the pressure exceeds the set value. The period of rising pressure is used to confirm that the oil pressure pump is not operating. Question: Is this hydraulic oil particularly special? What are the commonly used grades? As far as we know, some manufacturers working underground recommend Mobil 32...... (we couldn’t find out the exact grade), while panel manufacturers recommend Shell 24....... Does anyone who is familiar with these two types of oil know more about them? Is it very special? Additional information: The investigation revealed that the temperature ranges from 11 degrees in the early morning to 29 degrees at noon; under such conditions, the oil pressure of this type of oil increases by about 3 MPa due to the influence of temperature. Is this normal? Thank you so much! Urgently awaiting guidance.