Many cars these days, including BMWs, require premium gasoline to operate properly. The reason is because the engines in these cars operate at a much higher compression than the older cars in order to meet the Environmental Protection Agency's strict standards on emissions. What the manufactures don't really advertise, unless you read the operators manual, is that you can actually get away with lower grade gasoline. You can even use base grade if done right
Fill the tank with high-test 91+ octane gasoline when it is almost empty. This will help the engine run well, and clean out any carbon buildup.
Run the vehicle to half a tank, then fill with 87-octane fuel. This will give you mid-grade fuel of 89. The BMW engine is rated for 91-octane fuel.
Run the car till it needs fuel again and fill with 89-octane. At the next fuel stop, repeat the process starting with high-test fuel. This cycle will allow you to run regular fuel in the BMW 325.
