As the term 'top oiler" implies, it was intended to circulate lubricating oil to areas of the engine that were at the far end of the oil galleries/passages in a motor. They are intended to extend engine life by keeping moving parts and surfaces coated so they produce less friction and do not get damaged due to heat.
The only thing to note is that oilers were intended only for specialized applications..stationary engines that ran at steady speeds and may not get full lubrication or coolant flow, operations in higher temperatures on a consistent basis, and so on. If cars really needed it in all situations either it would have been part of the original engine design or the factory would have offered them as dealer-installed accessories.
