Stupid maybe Easy Question re: gas types

My son has a 94 Nissan Altima with 194,000 miles on it. The previous owner always used 91% octane (or higher)and thus, up to this point, so have we. With prices the way they are, what would be the harm in switching to regular unleaded?

Look in the owners manual for the recommended octane fuel the vehicle manufacturer recommends. If it states that a low octane fuel is recommended, then your son and the previous owner have been wasting money using a high octane fuel.


Repeat after me:

High Octane gas does not help an engine that does not need it. Octane is not a measure of quality or power.

Octane is a measure of how easy the gas starts to burn or how fast. High octane means it is hard to start burning. On the other end diesel is measured by certane and a high certane number means it is easier to start burning.

High octane gas may or may not have more additives like cleaners in it, but with today’s regulations any gas has enough for most engines.

   The owner's manual will say that it must have high octane or that it may use regular but should use high octane.  The parts the leave out are:

  * If it needs high octane, using regular can damage the engine.

  * If it should use high octane then it has a system to sense the low octane and to make adjustments to the car that will protect the engine.  However the adjustments will result in lower mileage (reducing or wiping out any economic advantage) and will reduce the power, defeating the reason most people buy cars that require high octane. 

  * Using high octane in a car that does not recommend it very very seldom causes damage but cost you more and offer no advantage.