I am trying this out....filled up last night with midgrade and will try the next three tanks with this.

 

Lawndart,
That's great. It will be interesting to see what our stats are for comparison. Sometime in July I suppose.

 

I thought about doing this too, but it would (hopefully) be early September before I would have the third tank finished .

 

I would have to take the skeptical side. The small difference in octane rating between regual and mid-grade (usu 89 oct) is not enough to make that much difference in performance.

As stated in various ways above, there are so many other variables, that is would be difficult to prove any real difference unless you had a "virtual shadow car" that drove exactly as you do with another grade of gas for a reasonable amount of time.

Higher octane gas does actually have higher energy per volume (indirectly, allowing higher pressures and temperatures before autodetonation), hence the reason for the differences. However the differences are not large enough to account for your stated differences.

 

A little sweat never hurt anyone!

 

I agree and that is why I suggested the method that I did. When he switches back to regular his mpg will have the added benefits of warmer weather, a car that is further along on it's break-in period, and a driver more used to driving it. As long as he doesn't skew the results with too much A/C usage it should be some interesting results. I personally think his 3 tanks of regular will show about the same mpg, if not better. Just for giggles I am willing to try the same, although I won't need to fuel up for another week or so. Only have 320 miles on this tank and still have over half a tank to go. As for my A/C usage, I rarely if ever use it, so shouldn't be a factor with my car. Where I live in PA is actually further south than Chicago but has lower mean temp in the summer months. Like I said before it should be fun, interesting, and might even prove myself wrong although in this case I don't think it will.

 

My first tank of mid grade results are in.
59.9 mpg for 495 miles measured at the pump.

The car computer displayed 57.4 mpg. I noticed this discrepancy during my first 3000 miles and decided to use my calculations at the pump. What's up with that?

I have only found this forum a week ago and am quite pleased with the help and information I receive.

Thanks All!!!

I always use the same pump at the same gas station for each fill up to insure accuracy.

I think the break in period is partly responsible for the higher numbers. I travel about 90 miles round trip per day. Similar conditions each way. This week was hot and windy. A/C for about half the tank.

 

The computer will not be as accurate as your calculated results, there are a lot of variables in it's calculations and is only an apprx value. I have found if you keep one of the trips just for lifetime mileage that it all averages out after a while.

 

Also, keep in mind that higher octane means more ethanol or a few more additives to suppress engine pre ignition. It has been rumored that increasing the ethanol content to 30% will increase perfomance and FE. This was in a previous thread on mixing your own fuel.....

 

You mentionthe midgrade gives you the best Miles per dollar, but then provide a MPG results. what was the break down of the MPD by grade? Can you provide those numbers?