Originally Posted by RiceCake
In terms of this site, Mobil 1 AFE actually isn't a bad oil, but the science behind it all gets fairly complicated. The best oil for fuel economy is the thinnest oil you can run at operating temperature, with the thinnest profile at cold temperatures.
These are your 0W-20, 0W-30 oils for the most part since the first number just dictates how easily pumped the oil is when cold, the lower the better. Does your call call for 5W-30? Try 0W-30 if you can find it. 5W-20? Try 0W-20. If it says either 5W-30 or 5W-20, try 0W-20, since its thinner at operating temp.
And realistically, you can use 0W-20 or 5W-20 in a car made for 5W-30. My car only specifies 5W-30 but later models just "suddenly" started suggesting 5W-20. The difference in oil thickness isn't a lot between 20 and 30 weight - most worn out 30 weights are the same as a 20 anyhow. So if you're particularly anal about getting economy and want the (maybe) %0.5-%1 improvement and don't mind being a little on the darkside if your manual doesn't say you can, run a 20.
But beyond that the best oil is complicated and based on cost and a variety of factors. I run Mobil 1 Delvac Elite 222 - a diesel motor oil in my car. Why? Well its a 0W-30 first of all and designed for easy starting of big diesel trucks in cold Canada winters, and in a car its fantastic. Second its loaded with an older zinc-based antiwear additive that they phased out on gasoline cars, so I get free extra wear protection. It also helps make me feel good that its a "true" synthetic but don't let that scare you. A lot of people overstate the difference between "group III" and "group IV" (or PAO synthetics), the latter being the only ones truly "man made". It also helps that being a diesel oil, they expect you to buy something like 15 liters of it and its marketed way, way differently -- it was cheaper at a distributor for Mobil then I can get Mobil 1 AFE, even on sale!
But it didn't stop me from buying a jug of Quaker State 0W-20 to try next winter. Why? Well it was really cheap and I wanted a 0W-20 to run in the car, something you can't get in diesel oils.
About the only major argument you can make is some oils are "a little better" or tailored a little more to specific situations. For the layperson? Oil is oil. Just buy the right oil. The number of people running 10W-30 or 15W-40 for absolutely no reason is insanely high. Or even worse, having people say you need oil "stabilizer", thicker oil for driving to Church on a Sunday, or even people saying you need a 10W-30 for winter -- the confusing rederick you hear in the oil aisle is frustrating.
Check your manual, buy the thinnest weight you can run, and buy a decent oil that meets the SAE requirements your manual calls for, and be happy.
If you have the choice of running a synthetic, you can go to 0W-20 or 0W-30 and *maybe* get a free half an MPG, but it really won't be measurable. The car will definitely be happier starting when cold and might start easier if it gets properly cold (like -30 cold) where you live.
The only benefit for running a synthetic after that is extending your oil change interval, which may or may not void your warranty. If you're changing a synthetic out every 3000 miles you're wasting money, period, use a regular oil. In my case the car calls for a 3000 mile oil change, but I run it out to 7500 miles on the Delvac Elite 222 I run.
And for the record, I just love saying I only run "Delvac Elite 222". It sounds awesome and usually generates nothing but "car guys" telling me it doesn't exist or its going to ruin my car and how I should run Royal Purple or some overpriced garbage.
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