Oil separator for internal combustion engine

An oil separator for an internal combustion engine, the oil separator comprising:

• a case including inflow ports into which blow-by gas flows, a gas outflow port from which the blow-by gas flows, and an oil discharge port;
• and
• a separation wall located in the case, wherein
• the oil separator is configured to separate oil from the blow-by gas on the separation wall and discharge the separated oil through the oil discharge port to an outside of the case,
• an upper side in a vertical direction is simply referred to as an upper side,
• an inside of the case is divided by the separation wall into an upstream passage and a downstream passage, the upstream passage being located on an upstream side in a flow direction of the blow-by gas, and the downstream passage being located on a downstream side of the upstream passage in the flow direction and located on the upper side of the upstream passage,
• the inflow ports and the oil discharge port are connected to the upstream passage,
• the gas outflow port is connected to the downstream passage,
• the inflow ports and the oil discharge port are arranged in a direction intersecting the vertical direction,
• the separation wall includes one connection passage that connects the upstream passage to the downstream passage on the upper side of the oil discharge port, and
• the separation wall is located on the upper side of the inflow ports, wherein the separation wall includes a lower surface, part of the lower surface being located immediately above the inflow ports.