The oil aeration in a V-6 spark-ignition passenger car engine under motoring condition was measured by the X-ray absorption method in the speed range of 2000-6000 rpm. Measurements were made at different locations in the sump representing the state of the oil at (1) the pump inlet, (2) the head return, and (3) the timing chain return. The aeration of the block return was estimated from these measurements. At a fixed engine speed, the aeration (in % volume of air) of the head return and the chain return were about the same, and they were approximately twice the value found in the block return. This distribution did not change with engine speed. When weighted by the flow rate, however, the block return contributed to 55% of the aeration at the pump inlet; the total contribution of the head return and the chain return was 45% (36% from head return and 9% from chain return). Further aeration observations were made by comparing the cases with and without the oil sump windage tray in place. When the tray was removed, aeration at the pump inlet was found to increase by less than 30% for all speeds.
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