337 Oil Diluters.

[skymstr02]

That was a carry over from the radial engined airplane days. What you did was to hold that switch just before the engine was shut down on the previous flight, this would pump raw gasoline into the oil sump, diluting the oil. This was for preparation for a cold weather start, and you would get oil pressure earlier because the oil was thinner.

This was good in theory, but not in practice.