very small portion of the oil is cooled not all of the oil. There is a restriction in line with 2 mm orfice . The oil flows to the oil pan not directly to the engine. I am looking and converting to a full flow oil cooler and I will put a inline temp thermastat to only cool when it reaches the operating temperature. The oil pump on the Z is high flow. The other weakness is the oil pan is relatively small compared to other engines. For example, the Toyota inline six and V8 hold 5 and 6 quarts respectively.