Saturday, April 12, 2008

Tank # 5

I filled up at Meijer yesterday. Here are the stats:

Price E85: $2.94 a gallon
Price 87 Octane gas: $3.44 a gallon

Gallons E85: 4.002
Gallons 87 Octane: 9.830
Gallons left from tank 4 (@~30% ethanol): 2.568

The difficulty is that we are in the transition from winter blend E85 to summer blend. The ethanol content of E85 at this time is unknown. It can be anywhere from 70% to 76%.

Worst case, this tank has a little less than 28% ethanol. Best case, it's 29%.

Octane would be similarly difficult to figure out. I think that, worst case, it is a little over 91 octane.

Tank 4 finished with a mileage of 24.5. So far, I've done about 15 to 20 miles of local driving, and the mileage is right at 20.

Not bad.


Anonymous said...

Assuming the 70% base RBOB is 85 suboctane and 30% is approx 113 octane- then your r+m/2 should be around 93.4. However- the ethanol is much higher in research octane and less so in motor octane. Thus your sensitivity is wide and if your Saab likes high motor octane it might act a bit more like a 92.

Buzz- have you noticed at higher levels of ethanol that you are better not stopping for donuts after a cold start until you have driven a few miles? I have not seen this so much with E20-30 but this really shows up on FFV's running straight E85. Cold idle and stopping too soon is a non-no for mileage on them.


buzzcut said...

I was making a slightly different calculation. I started with E85 (really E70) at 100 Octane, and calculated with that. I didn't try to break down the E85 itself.

My Saab takes a long time to warm up and has awful mileage at startup, even on E10. It is worse in the winter. I have not noticed it being any worse with the E85.

In fact, for whatever reason, I made all the lights on Indianapolis Blvd. from Meijer to the Borman. That's like 5 miles or so. I had the cruise set at 45 and had the tranny in manual, locked in 5th gear. My mileage went from 22.8 to 23 over that stretch, even though the car wasn't fully warmed up. Usually I lose a fraction of an mpg if I hit a couple of lights or it's cold out.

In contrast, after I got on the highway, I set the cruise to 60, drove another 10 miles on the highway, and the mileage only went from 23 to 23.2. I'm at about a half a tank, and the mileage gets very steady at that point.

I guess that I've driven more local on this tank than the last. I'm going to try to record average speed per tank to try and get a better feel for the breakdown between local and highway.

Anonymous said...

There are a bunch of drivers in South Dakota who have been running their cars on only E-85 for a long time and not run into any problems. It's detailed in the book

which I strongly recommend. I ran a 93 Olds on half e-85 when I was in Pittsburgh (where they sell the stuff, they don't near where I live) and didn't have any problems. Oh, the fuel pump might get all gunked up pushing up clean fuel but if you switch over slowly, this isn't a problem.

Check out the book.