Makers of cars & light trucks sold in the U.S. are pressured by the EPA to do everything to reduce fuel consumption. Lighter viscosity oils do reduce consumption a percent or so. The owner's manual for my '01 allows either 10W-30 or 5W-30 except in frigid weather, but says that 5W-30 is "preferred." This allows Toyota to use that oil in their fuel mileage testing and show those slightly better results.
Ford, Honda, and Dodge are recommending 5W-20 in some or all of their engines now. The same engine sold overseas will have a higher viscosity oil recommended for it. Often, 5W-20 is not even available at those overseas dealerships. Folks talk about lighter oil getting to the top of the engine faster, but I haven't seen any documentation. BMW requires 10W-60 synthetic in some of their overhead cam engines. 20W-50 is used in our V8 engines in other countries. No top end problems noted in those cases. My preference is still to use the highest viscosity oil permitted by the owner's manual, or maybe even one viscosity grade higher if the engine is worked hard and hot.
Ken
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You get what you inspect
Not what you expect.
S&S Long Tube Hi-Torque Headers
TRD/Eaton Limited Slip Differential
Gibson exhaust system
Hellwig Rear Antisway Bar
Sylvania Xenarc H.I.D. X1010 Auxiliary Low Beam Driving Lights
Schaeffer Engine Oil, ATF, Differential Oil
Racor LFS22825 full-flow transmission filter
Towing a 21' Bigfoot trailer using a Hensley Arrow hitch, Jordan brake controller, McKesh mirrors
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