[Taxman]

Why does the same Gas tanker that services Top Tier stations then drive across the street and service the non top tier stations.

The tanker driver has to set the mix when he delivers, the detergents aren't in the big tank on the trailer.
For example, he might put 150ppm of the Marathon/STP additive package in Speedway's underground tanks and 400ppm of the same detergent in the Marathon station's tanks. (I'm working from memory and might have the numbers wrong, but there's a lot more of the stuff in Marathon gas than there is in Speedway) Then he drives to the Shell station and mixes entirely different additives in the gas he delivers there.

That's why it surprised me when an earlier post in this thread mentioned Speedway as one of the best fuels.

What's interesting is that all grades of Shell are Top Tier certified, but Shell Premium is advertised as having something like twice the additives as Shell Regular and Midgrade.

Around here, 93 octane costs 60 cents per gallon more than 87 octane, except at Shell stations where it costs 70-90 cents more than 87. Some of my cars that don't get driven much get Shell 93 under the assumption that it has way more detergent than is useful in normal driving. The low fuel light came on in my S420 last month and I planned on filling it the next time I drove it, but I haven't driven it lately so it still has 2 gallons of Shell I bought back in March. I should have filled it last week, now it's probably too late to get summer gas for it.

 

[Taxman]

I had about 5 gallons of Marathon 87 octane E10 in my 2.2L Ion this afternoon when I dumped 2 gallons of E85 in it and drove it to town. The car didn't care one bit. I even ran it up to 4000rpm WOT, no discernable difference. Got to town and put another 6.4 gallons of Marathon regular in it.

So I suspect, but do not know, that the PCM in a Cruze can deal with 4 gallons of E85 in a full tank. I do know that a 2007 Saturn Ion's Ecotec can deal with it.

The next question is whether it would do long term harm, as the Cruze 1.4 is not certified for over E15 in USA.

 

[Taxman]

E85 is equivalent to 105 octane

Maybe E100 is 105 at (R+M)/2, but E85 isn't.

Sunoco Race E85 is claimed to be 99 octane (104 Research, 94 Motor, 99 avg), and I doubt the $2 a gallon stuff is any better.

 

[Taxman]

But as a cost savings measure it seems like a poor solution.

I found it at a Valeo station on the other side of the state back in June, 93 octane was $2.83 and E85 was $2.28, which is poor economics for the E85. I bought a couple of gallons to play with and stuck it in my Saturn, filled the Mercedes with 93 octane, which was over $3 where I live. (now over $3.50)

I've seen cars that were EPA rated 40hwy with 87 octane and 30 hwy with E85, which implies E85 is less miles per tank at 3/4 the cost of E10, and a money saver at 2/3 the cost. You just almost never see it for under 70% the price of E10.