I learned something today. I mean besides the fact the HS drop-out oil change boy thinks everyone is dumber than his "computer". Some auto mfg's have retroactively changed their oil recommendations to be able to revise many years worth of mileage data to insignificantly increase their CAFE standards rating (Corporate Average Fuel Economy (CAFE)). Most notable are Honda and Ford. Why? Since every manufacturer has to maintain a minimum mileage standard averaged across all vehicles adding .05 MPG might help keep a big SUV in your line-up for another year or two. These vehicles represent the highest profit margin. You need to keep in mind that over 70% of the cost (value) of the average vehicle is in the electronics, computers & wiring. So, a Ford Focus with all the safety perks has about the same electronics cost to build as an Expedition! The difference is a few thousand bucks of steel & plastic and maybe a DVD entertainment system.
Why should I care? Well switching from 5-W30 to 5-W20 could have an adverse affect on your car's motor. Actually, switching back and fourth between any different brand and viscosity of oil could cause harm anyway. All oils are formulated with manufacturer specific detergents & lubricants so switching from one to another could be loosely compared with abruptly changing your own diet. More specifically, you are changing the grade of your oil. Let us look at the numbers: 5 = the cold weight of the oil. This is the weight when you first start your car in the morning. Between the two grades this number is a wash. 20/30 = the weight of the oil at operating temperature (aka hot). The 20 is much thinner at temperature than the 30 is. In an older engine regular use has increased the tolerances and spaces between moving parts, oil pressure has dropped over time and seals are not as tight as they once were. The thinner oil is being asked to work harder. The films may deteriorate before new oil can be pumped in, just simply leak away because it is a thinner liquid, or simply fail because it is not being used in it's intended application. If you drive in city traffic, tow anything, have frequent starts & stops or drive your vehicle hard you may be lessening the life of your motor and not even knowing it.
Meanwhile, oil change drop-out boy is just following what the computer says and does not give a crap about your motor. Also, for some reason most establishments charge an extra $5 for the 5-W20 oil. A coincidence? Maybe not. Go to the local auto parts store and see if there is a $1.25 per quart difference on the shelf. Interestingly enough, my motorcycle that can rev as many as 11000 RPMs (Sports cars can rev about 5000) requires 10-W40. There are no CAFE standards on bikes. So, if you are not diligent you may (read: you will) get a lighter grade of oil in your vehicle at the Kwiky Lube. Don't wreck your car or truck because Honda and Ford want to sell a few extra mini-vans and Expeditions. In the end go with what the manufacturer recommended when your car or truck was built, not with what they are saying now because of politiking. If you don't pay attention the next one they sell might be to you?