* The difference between the gasolines: Switching between brands of regular unleaded (all meeting the same octane rating) will likely have minimal impact. However, switching from regular unleaded to premium, mid-grade, or E85 (ethanol blend) will definitely have an effect.
* Your car's specifications: Your owner's manual clearly states the recommended octane rating and fuel type for your vehicle. Using a lower octane than recommended can lead to knocking (pre-ignition) which can damage your engine over time. Using a higher octane than recommended is generally harmless (your engine will simply not utilize the extra anti-knock properties), but it's a waste of money. Using a different fuel type (e.g., putting E85 in a car not designed for it) can cause significant engine damage.
* Frequency of change: Occasional use of a slightly different gasoline (e.g., a higher octane once in a while) is unlikely to cause problems. Regularly using an inappropriate fuel type, however, is damaging.
In short:
* Sticking to the recommended fuel type and octane rating in your owner's manual is always the best practice. This ensures optimal engine performance and longevity.
* Minor variations between brands of the same type and octane are usually negligible.
* Significant changes (octane rating, fuel type) can lead to decreased performance, engine damage, and increased wear.
If you're unsure about what type of gasoline to use, always consult your owner's manual. If you accidentally use the wrong type of fuel, it's best to avoid driving excessively and fill up with the correct fuel as soon as possible. In some cases, significant mis-fueling may require professional attention.
