DRIVERS ASK, TOM ANSWERS:

MAINTENANCE PROBLEMS SOLVED

Dear    Tom,

Q Does a car get better gas mileage with 89 octane? And why do some cars

require it according to the manuals? I own a 2008 Acura TL and the manual
recommends 89. With gas prices the way they are, I want to know if it is
necessary to buy the recommended octane. Thank you.

Sam—Minnesota

Sam,

A Octane has nothing to do with fuel mileage and everything to do with

volatility or stability within the combustion chambers of the engine. Low-
octane fuel is less stable inside an engine than high-octane fuel. High-
performance engines like yours operate at higher combustion chamber
temperatures due to higher compression ratios. When low-octane fuel is
introduced into a high-compression engine, it pre-ignites, causing a
phenomenon called “engine knock.” The fuel ignites before it has properly
compressed and the electrical spark introduced at the precise time for
maximum efficiency. This pre-ignition causes hammering on the tops of the
pistons, cylinder head, and valve faces. Over time, this results in premature
engine failure. Use the recommended octane fuel in your engine; it’s cheaper
in the long run than replacing the engine.