Multi viscosity and detergent oils are....newer than the trucks we play with. Go figure. A 10-30 oil flows through a metered hole at low temps like a 10 weight straight oil. It also flows through a metered hole at 200 degrees F. like a straight 30 weight oil. Same with 20-50 or 5-20 or what ever. Detergent oil works(ever spend the day cleaning out a paraffin based sludge motor?). What we(old truck motors any way) want is an oil film between the moving bits. Air cooled motors..different animals. Not a lot of cooling(some I know, but not a lot) from the oil in our beloved engines. We have ..WATER for that. All fluids have viscosity(some more and some less) Measures are in Centistokes(look that one up if you must), "weight" and other standards. All involve, Time, Volume, Temperature, metered orifice and, Gravity. Opinion here. In the summer I use 20-50. Makes me feel better. It does get over 100 degrees F in my home town(Ogden Utah) so I just feel better. I also use 10-30 in the winter. Cold starts are evil. 10 weight oil flows better cold. So there you have it. Detergent, good. Multi viscosity, good. Rant done. Enjoy driving your truck.
