|
You may want to have your car diagnosed. There is no way you should get 10mpg better fuel economy between 87 octane and 91+ unless there is a problem with the car. Higher octane contains less energy due to reduced burning efficiency. You may have a problem with a knock sensor which causes a reduction in ignition timing and therefore efficiency. In very high mileage "engines, the build up of carbon deposits on the pistons can cause similar issued by raising compression ratio or creating hot spots.
No matter what the cause, there is no way that you would observe such a difference in mpg in a properly running vehicle (designed for 87 octane) by the simple addition of higher octane fuel. This has been tested quite thoroughly.
|