One easy way to gain an estimated +0.2 to +0.4 MPG is to use a special engine oil I found recently. Eneos Racing Street (RS) 0w-20, a qualified API SN GF-5 oil I got from Amazon.
What makes it different than, say, a typical 0w-20 like Mobil1 AFE 0w-20:
- Friction Modifier (reducer): Eneos has 900 ppm moly; Mobil1 has 88 ppm moly.
- Viscous Friction reduction: Eneos has a KV40 of 29 cSt; Mobil1 is 45 cSt.
- Both are full synthetic. Eneos's base oil is all Group3+ (like Pennzoil Platinum's PurePlus base oil), while Mobil1's base oils is about half PAO, half Group3.
- Both oils have the same, usual, typical HTHS 2.7, which indicates how much hydrodynamic lubrication conditions happen in an engine, and its important to be at 2.7 here, kind of an important number which both oils have.
- I know the word 'racing' is in the name, next to the word 'street', yet the API SN GF-5 rating means this is a fully qualified street engine oil.
More moly (Molybdenum compounds) is actually quite protective (wear) as well as reducing friction, and Eneos has a lot more. Several Japanese oil formulators like Eneos take a high-moly approach for some unknown reason, getting more friction benefits than just the minimal necessary to pass the certification specifications. Another story there I won't go into.
The difference in viscosity (KV40 for example) will help an engine during cold-cool-warm operation to get better MPG via less viscous friction drag. Especially pronounced in the winter, yet will help in summer too.
Base oil is of very good quality & performance, as Group3+ is a great performer, very similar to Mobil1 going with half PAO, half Group3 (note their Group3 is not Group3+).
Eneos Racing Street 0w-20 does cost more. I ordered a 6-pack from Amazon and it was $66, no tax, no shipping (Prime). Not cheap, I know.
Only for hypermilers or somebody who really values extra MPG here.
Mobil1 AFE 0w20 at about $5 per quart in big jug is the bargain at Walmart, yet without all that moly & better viscosity.