Why does the B-29 have eight oil needles? In the image above, quiet flyer and I realized that there are 2 needles in every oil gauge, and there are 4 oil gauges. Well, why in the world are there 8 needles in total? And the optimal range arcs and redlines of each oil gauge is different. Why would that be? Oil is oil, I can't see how the optimal range arc for some oil in one gauge is different from the optimal range arc for some oil (same oil, oil is oil, the B-29 does NOT run on multiple oils. It isn't an eco-plane and it drops bombs. It has no need for more than one oil) Any thoughts would be great. Solving questions concerning something like dials and maximum speed with flaps extended for such an old plane have answers that are hard to come by, since they would have had to note this stuff down on paper and not electronically, and the people who built them are either very, very old; or unfortunately dead.
Each of the four engines is represented by two needles, one in each row. The top gauges are for the nose oil; the bottom gauges are for the rear oil.
Nose and rear here refer to two sections (remember that's a twin-row radial engine). The nose case oil is also used by the propeller's governor, feathering mechanism, and reduction gear – those would explain the lower pressure range of the nose section.
During development the nose case was troublesome:

Reduction gear failures started to occur during extended climbs, forcing the addition of external oil lines from the accessory case to the nose case to shore up low nose case oil pressure (enginehistory.org; PDF).



B-29 commander training manual

More on Google Books: United States. Army Air Forces (1950). Technical Data Digest. p. 26.