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The oil aeration process in the crankcase of a V6 engine was visualized with a high-speed video camera and a borescope at engine speeds up to 4500rpm and oil temperatures to 70°C. The video images showed that a high-speed oil droplet stream was flung from the crankshaft counterweight, passed through the oil drainage gap in the windage tray and struck the free surface of the oil in the sump. There was a speed threshold beyond which foam was observed to form on the oil surface. When the engine speed was reduced to below that threshold, the foam disappeared. When the windage tray was removed, there was no foam formation. The results suggested that foam formation was the net result of the balance between the air bubble formation and destruction processes. These two processes were speed dependent.