The crankcase ventilating system is used to remove water vapor, fuel vapor and combustion gases (from blow-by past the piston rings) from the crankcase thereby preventing undesirable combinations of these compounds with the engine oil.
Air is driven into the opening of the oil filler pipe cap by the fan draft and, after being cleaned by [...]

Here are the tune up specifications for the 1941-1953 Pontiac 6 and 8 cylinder engines.

What you need to know about the Flathead engine oiling system.