The owner's manual for my 2005 Nissan 3.5S indicates that preminum gasoline is required. Is this necessary?

Q: The service manager at my local Nissan Dealer told me that I could use regular unleaded gasoline with no ill effects.

A: Lots of the usual misinformed junk here. It is true that your engine has a sensor to detect incipient preignition (ping or, worse, knock). So if you use a fuel with a lower octane rating than the manufacturer recommends, the sensor will signal the engine to retard the spark and richen the fuel mixture to prevent damage. Because retarding the spark makes the ignition occur later in the combustion cycle, when the piston has already started moving down in the cylinder, the explosion from that ignition is pushing on the piston for a shorter part of the power stroke. Thus much of the explosive effort is wasted because it's still pushing when the piston gets to the bottom of the stroke and the exhaust valves open, letting a lot of the power just blow out the exhaust. That, combined with the richened fuel mixture, makes your engine use more fuel than it would with the recommended grade of gas, for poorer performance, and much of the money you saved buying regular gas is spent buying gas more frequently. So the strategy is not very cost-effective. On top of that, there is the (admittedly small) danger that your engine might suffer some damage from preignition despite the built-in protection. If that happens, and in the pre-repair inspection they discover lower octane gas in the tank, you just blew your warranty (if you had one), and all repairs are at your cost. Finally, it's a shame to not to get the full benefit of the performance of that great VQ45DE V6 -- sort of like buying a convertible and never putting the top down!

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