A display of LED’s with different color illuminates under a transparent cover. After power is turned on, the green LED’s start flashing, indicating that the system is active. A pressure sensor continuously controls the pressure loss in the filter head and a temperature sensor simultaneously registers the temperature of the fluid. After the oil has reached the operating temperature (which is typically above 86°F), the green LED’s stop flickering. (which is typically above 86°F), the green LED’s stop flickering. The sensor then is in operational mode. The signal points can be set closer to the cracking pressure of the bypass valve due to the high accuracy of the pressure sensor. This allows more use of the total dirt holding capacity and saves operational costs at the same time.