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There once was a time when it was highly important to run the correct octane fuel in an engine. Older cars were not equipped to handle the difference at all. The result would be uncontrolled combustion that would eventually cause the engine to knock. Modern engines are equipped with sensors to help regulate the flow of fuel and monitor the rate of ignition to ensure everything stays within a safe operating range.
One of two different declarations will be found in the manual about standard fuel. Premium Recommended engines can be used with a lower octane of gas. Premium Required engines are a different story altogether. One can run a lower octane in a Premium Required engine but it is best not to do it regularly. That type of engine can be damaged by the way a lower octane fuel ignites.
Engines of the past were unable to adjust to fuels with different octane ratings. The wrong fuel would cause audible knocking as the combustion became uncontrollable. The knocking would do damage to internal engine parts over a long period of time.
In situations where a lot of throttle is used, lower-octane fuels do not allow the engine to run as much ignition advance. Additional ignition advance lets the engine generate more power during hard throttle situations. Thus, if a lower-octane fuel is used with a Premium Recommended engine, then the engine is producing less power in hard accelerations. This loss is generally in the neighborhood of about a half mile per hour from 0 to 60; barely noticeable for most drivers. Drivers with a turbocharged gasoline engine will notice the difference much more.
This difference really only stands out for those that make heavy use of the throttle. In partial conditions, full ignition advance with no knock is readily attainable regardless of the octane of the fuel.
A vehicle that has an engine that requires premium is a different story. Running a lesser octane fuel can result in higher exhaust-gas temperatures and knocking that will do significant damage to the interior components of the engine. The relatively small amount saved from running a lesser fuel in a Premium Required engine will not offset the cost of having to buy a replacement engine.
If your manual cites your vehicle as “Premium Recommended”, lower octane can be used by driving gently and not using the throttle hard. It will be nearly impossible to tell the difference in performance for most users.




