Possible reasons:
(1) The oil is too dirty.
(2) Oil filter failure or detachment
(3) The oil viscosity is too low.
(4) Oil temperature (due to low cooling water volume, scaling of cooling water pipes, or scaling of coolers).
Troubleshooting:
(1) Change the oil.
(2) Check, repair or replace.
(3) Replace with high-quality hydraulic oil.
(4) Increase the cooling water volume, flush the water pipe, or replace the cooler. (When turning off the pump, it must be turned off first and then the water must be turned off, otherwise the mud will flow into the cooler and become blocked.)