I am frequently asked if the fact that a car has been fueled with a certain brand of gas, or a certain type of oil has been used — perhaps synthetic — means that now the car needs to continue with the same diet. Not really, as long as the fuel is legitimate and meets the vehicle manufacturer’s octane requirements and as long as the motor oil meets the vehicle manufacturer’s specs, you will be fine. If a long term vegetarian tells me that they decided to go wild and gorge on roast beef and that caused a severe gastric or other reaction, I would believe that their body could not handle what it become unaccustomed to. The automotive engine does not yet have such sophisticated adaptive mechanisms to become dependent on a certain brand of motor oil. Maybe in a few years! In fact I will qualify my statements above to point out that “flex fuel” vehicles measure the percentage of alcohol in the fuel line electrically and signal the computer to adjust engine parameters accordingly. But short of a software or mechanical problem these cars can go back and forth with no problem.