Re: Engine Oil
YES! You can technically run any grade of oil you want. On some V8's that have cylinder deactivation (mainly Dodge), requires a 5W20 oil or lighter for the system to operate properly, but otherwise you could run 15W40 in an engine if you really wanted to. I know a lot of fleet vehicles that use 15W40 even in gas engines as it simplifies inventory and the gas vehicles don't see high speeds (under 65mph).
5W20 is more of a fuel economy measure. Lighter weight oil means less frictional loss. Not that the average consumer will notice the difference, but the EPA might as the tests are conducted indoors, and under optimal conditions.
I run Amsoil 0W30 in all my vehicles. My Dodge and Pontiac call for 5W30. My '99 Taurus calls for 5W20. I've noticed better starts in warm and cold weather, and better mileage under low traffic, low to mid speed highway conditions than running a heavier weight oil. I also run synthetics in the transmissions and axles, where applicable.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!