It looks like you're new here. If you want to get involved, click one of these buttons!
Cadillac CTS/CTS-V: Real World MPG
Second, after the earlier discussion here on octane, I drove from Chicago to Toronto and back over the weekend, about 1200 miles. Used 93 octane going (which I had been using exclusively) and 87 returning. I always drive until the Low Fuel message, then invariably put in 16 gallons (the tank holds 17.5 per the manual), so by the second tank I think the residual 93 octane was negligible.
There were absolutely no differences in driving perceptions, highway, city or expressway, from one octane to the other. However, I did experience what I consider a very strange mileage phenomenon.
Keeping track of fuel consumption was really weird, because as soon as I crossed into Canada, I had to start using litres and kilometers (it's the law there, and you have to do it in French under risk of being arreted). Very confusing, especially when you multiply the metric hours by Canadian dollars and then convert everything to Celsius. Thank heavens the CTS has a computer to manage all these factors.
Anyway, driving east with 93 octane I got 24.0 mpg. Returning with 87 octane I got.....are you ready?.....26.4!!!! Both segments were essentially identical, highway speeds about 80 mph, negligible wind, comparable weather and the same terrain, and both cities are close to 600 feet above sea level, so it wasn't uphill one way and down the other. Temperature going hovered about 32F and returning was about 38F. I can't explain the difference, particularly the better mileage on lower octane fuel, unless the car just happened to "loosen up and break in" while on the trip (I have about 8K miles now).
In any event, I am going to use 87 octane from now on, unless something happens to change my mind.