Since I rebuilt the transmission on my Whirlpool over 2 1/2 years ago, gear oil is more sticky and is designed to ‘climb up’ moving gears inside a gear box wether it be a automobile manual transmission or a transmission inside a washer. On the input gear on a Whirlpool belt drive transmission (the pulley the gear attaches to), there’s a spiral pattern which pushes oil down into a area where there’s a small hole oil comes out which is a primitive sort of oil pump, my guess is Whirlpool built their belt drive transmissions to be backwards compatible with other oils which were non-detergent motor oils. Not sure if that’s correct, but it could be a possibility judging by the things I observed over 2 years ago. As for motor/engine oils, they have to be a certain viscosity since the oil has to be able to flow correctly at low and high temperatures through the main crankshaft and camshaft journals, especially important with modern engines with variable valve timing and overhead cams. Push rod overhead valve engines can get away with using a thinker oil if there’s significant wear and noise since there’s no overhead cams to lubricate, just the rocker arms for the intake and exhaust valves. Definitely won’t be good news to use thinker oils in modern overhead cam engines with variable valve timing since there’s very fine oil passages for the various parts and such.