richard-tx

I took two road trips recently and tracked the gas mileage on my 06 A8 with the 4.2 engine. The difference between 10% ethanol gas and pure gas was surprising. One way to tell the difference is to look at the octane rating on the pump. E10 premium gas is usually rated at 93 octane. Pure gas is at 91.

With E-10 gas I got 22 MPG at 82 MPH
Gas without ethanol yielded about 26 MPG at 82 MPH.

Has anyone else experienced this?

The cost of the E10 and pure gas was about the same. Gas prices varied more by location than type of gas. Downtown Chicago was pricey for E10. Almost $4 per gallon. Rural Oklahoma was cheaper for pure gas.

Mister Bally

(Has anyone else experienced this?)

Yes.

But the important test is 87 octane(regular gasoline in most areas of North America) vs. the minimum 91 octane which is Premium and the one only fuel Audi recommends in the 4.2L A8 you have.

The difference per gallon used to be 20¢. It is now typically 30-60¢. I have found less than .5MPG difference between the fuels. Thus, no benefit of the premium price. I only use premium when in mountain areas or on salt flats possibly driving at speeds shown in my avatar or in one of my albums.

2004A8L

What about mixing 91 with 87 ?
Say 8 gallons 91 and the rest 87

MP4.2+6.0

Then you get Ethyl/ the mid grade. In CA all gas has the 10% ethanol in it, so we're stuck. But meantime midgrade is typically just a mix from two gasoline tanks they have--regular and premium--at least here. When I was a kid, some station pumps even had a big clock hand sort of mechanical dial where you could pick your mix in a bunch of steps. For a long time in early unleaded days, many stations had no premium since one tank was leaded and the other unleaded. Or, once in a while diesel w/ a third tank. CA is also 91 octane with the ethanol; no std. 93 here. Plus typically highest prices in the lower 48.

My W12 and my prior A6 4.2 both ping a bit on regular--I can hear it on initial acceleration when running beside walls and other sound reflective scenarios. It goes away after first couple of seconds, probably as knock sensors kick timing down, though it was more persistent in 4.2. Akin to Mister Bally though, I will drop to mid grade for things like long freeway type trips with leisurely motor loads, or cooler seasonal conditions. Can't make out any real diff in MPGs. With either motor for me, that has a lot more to do with in town vs. open road driving.

richard-tx

I fail to understand why anyone would run regular gasoline in an engine where it is clearly stated in multiple places to use premium (91 octane minimum). See how quick your warranty will be voided (if you have any warranty left) if Audi found out that you are running regular gas.

This mileage increase is saw is due to the lack of ethanol in the gasoline, not the octane change from 93 to 91. Ethanol has less energy per gallon than gasoline. That is why more E10 gas is needed to run the 4.2 engine at the same speed and same load.

Since the Audi engines have a relatively high compression ratio (11:1 if I recall correctly), that means that the engine will knock if run on regular gas. Knocking isn't just an annoyance, it is damaging the engine.

Contrary to popular belief, high octane gas burns cooler than regular which means combustion chamber temperatures are cooler, valves last longer, etc.

I run premium ethanol free gas in my small engines. They start better, run smoother, and I don't have any carb issues even if it has sat for 10 months or more.

2004A8L

I would fill it up with Kerosene but it's not available at the pump
91 is the highest we have here

richard-tx

91 generally means no ethanol in your gas and that is a good thing.

2004A8L

we have here
87 + 10% ethanol
87
89
91

Not all gas stations have 91 i have to drive around and look for 91 lol.

Doc_A8

In Utes Land, 91 octane is the top, and it's all ethanol gas....

Highmile

Wow 4mpg is a big difference. I always run the highest available octane wich is usually 91, sometimes 93. "Contains up to 10% ethanol" iswhat I usually deal with Next time I come across non ethanol gas I will fill'er'up and log gas mileage.