PURPOSE: An oil filter system is provided to determine the time for changing filter using oil pressure of filtering by an oil filter and to display it to a driver. CONSTITUTION: A housing(12) of an oil filter(10) has an intake port(14) connected with an oil pump and an outlet port(16) to supply filtered oil to an internal engine. A filter paper(18) is installed between the intake port(14) and the outlet port(16) to filter the oil. A bypass valve(20) is formed with a ball(20a) and a spring(20b) to support the ball(20a). When the oil pressure is normal, the bypass valve(20) is closed. And when the oil pressure is increased by a cold starting or contamination of the filter paper(18), the bypass valve(20) is opened. A plunger housing(24) is provided in lower side of the bypass valve(20) connected with an ECU(22). In the plunger housing(24), a plunger(26) is supported by a spring(28). As the ball(20a) moves up, a contact terminal(26a) of the plunger(26) is contacted with the plunger housing(24) to send an electric
