Octane Has Nothing To Do With Fuel Mileage

Dear Tom,

Do you get better gas mileage with 89 octane and why do some cars “require” it according to the manual? I own a 2008 Acura TL and they recommend 89. Because of high gas prices, I want to know if I can use the cheaper 87 octane.

Sam from Minnesota


Octane has nothing to do with fuel mileage and everything to do with volatility or stability within the combustion chambers. Low octane fuel is less stable inside an engine than high-octane fuel. High performance engines) such as your Acura’s engine) operate at higher combustion chamber temps because of higher compression ratios. When low octane fuel is introduced into a high compression engine operating at higher than normal temps, it pre ignites, causing a phenomenon called “engine knock.” This is where the fuel ignites before it has a chance to be adequately 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 premature engine failure occurs. Use the recommended octane fuel in your engine; it’s cheaper in the long run! Best to you.


Dear Tom,

I have had problems with the brakes squealing since the day I bought my car. It’s a 2003 Bonneville, with only 24,000 miles on it. I’ve taken it to the dealer three times to be checked out. Each time they tell me that the brakes don’t need changing. What could be causing them to squeal, and is it any thing I should be worried about?

Karen from Jacksonville, Fla.


Here are the causes of brake squeal: Pad glazing (hardening or crystallizing), broken anti-rattle clips, missing pad insulators, no silicone pad insulation, bad brake pads (brake pad composition too hard), no camphor on the leading edge of the new pads, glazed rotors (in which case they need a non-directional cut applied for proper pad break in).

Get your vehicle in to a good repair facility to have it checked for these items.

Good luck to you.


Dear Tom,

I was reading about your article regarding oil changes in automotive engines at CNN.com and I have a question in regard to detergent and non-detergent oil. I know that today’s automobile engines use non-detergent. I have just recently rebuilt a 1955 Chris Craft boat with a flat head six-cylinder carburetor engine and I was advised that I should use non-detergent motor oil in this engine. My question is: why should I use a non-detergent instead of the detergent oil, which I understand will keep the engine cleaner? Thanks.



On the contrary, today’s engines use high detergent oil; that is how they stay clean of sludge deposits despite the high operating temps that they run (that’s assuming the oil is changed on a regular basis according to manufacturer’s specs). I see no reason why you can’t use today’s oil in your boat engine. The only concern is if the engine had not been touched yet and it had original seals and wear. Seeing that the seals have been replaced and OEM tolerances restored, go ahead and use the viscosity oil recommended by the engine builders in high-detergent oil. OEM recommendations are based on the rebuild. As a matter of fact, check out usage of synthetic oil. AMSOIL makes a great marine application that would work well in your new boat engine. Check it out at www.lubedepot.com.


Dear Tom,

I own a 2010 Audi and the engine light keeps coming on. I took it to my mechanic and he said I needed a new catalytic converter. I took it back to my Audi dealer and they said I needed new sparkplugs; they never mentioned the catalytic converter. They put new sparkplugs in and the check engine light still was illuminated. The told me that the light would go off after driving the car for a few hours, which was true but the light is back on again, I went for an inspection (California) and the car failed for emissions. The dealer wants to charge me again for a diagnostic and the car smells like rotten eggs. What is going on here?

Samantha from Fresno, Calif.


Call Audi customer service and get with your local service zone rep. You should have documentation that the catalytic converter needed replacing before the warranty went out. This should be enough to get Audi to pay for the replacement of the cat. But, make sure someone checked why the cat went bad – usually they go bad because of excessive fuel being dumped into the engine. The cat receives more gasoline than it can process. When this happens, a rock of carbon forms inside the cat restricting exhaust flow (kind of like it’s constipated along with the rotten egg smell). Catalytic converter replacement does not guarantee the problem is solved. Get to the root which is excessively rich fuel mixture or else this will happen again! I wish you success.


Dear Tom,

Help! My mom bought a used 2005 Honda and now there is an ear-splitting whistle that comes and goes. We did not hear it during the test drive. Next day, no whistle. A few months have gone by and some days the whistle is so loud and so relentless that you can’t talk or hear music. Sometimes Mom can use the car two or three times and not hear a thing. Sometimes it whistles for days. Can you help us?

Diane from Sawyer, Tenn.


Sounds like you might have a high-pitched vacuum leak occurring while the engine is running. These can be hard to track down because the leak (and resulting whistle) can vary with engine temperature (it can come and go with expansion and contraction of the metal). This can cause the manifold to leak when cold and seal when warms. I would try spraying carbon cleaner at the base of the intake manifold. See if the idle changes, specifically look to see if it speeds up. If it does, then you have found your leak. Replace whatever gasket is leaking. If no leaks are found, check the serpentine belt tension. The automatic tensioner may be worn in which case the belt is squealing when a load is placed on it (i.e. A/C compressor, power steering, alternator). Success to you.


‘Til next time … Keep Rollin’

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Tom Torbjornsen is an automotive expert of 38 years. An automotive journalist in good standing with the International Motor Press Association and Motor Press Guild, Torbjornsen has been the Repair and Maintenance editor for AOL Autos, At Home Portals, and many other websites. Hear his radio show AMERICA’S CAR SHOW, locally on AM1340 WKSN via the SSI Radio Network Saturday mornings at 8. See Tom’s television show, “America’s Car Show” on Buffalo’s all new WBBZ-TV, Channel 5 on Dish, channel 67 over-the-air and on DirecTV. The show airs weekly Wednesday nights 6:30-7 p.m.. It is re-aired on Thursday mornings at 9 a.m. and Saturday mornings at 11 a.m.. For more info on Tom Torbjornsen, visit AMERICA’S CAR SHOW website at americascarshow.com. You can send Tom your car questions and TV show topic suggestions at: tom@americascarshow.com. Find Tom’s book, “How To Make Your Car Last Forever” in local Barnes & Noble booksellers and Amazon.com.