Gas Octane


Old 12-06-03, 07:55 AM
dmitchelljr's Avatar
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Join Date: Apr 2002
Location: USA
Posts: 72
Gas Octane

My wife has a 2000 Nissan Maxima. A while back the service engine soon light came on and would not go off. We went to Auto Zone and they hooked the tester up to the car and all it said was too lean of a mixture. The boy said we probably got a hold of some bad gas. He reset the light and it did not come on again.

The other day the engine starting making a pinging sound when you accelerate. The service engine soon light has came back on. We burn regular 87 octane gas in the car. The owner's manual recommends burning high octane 93 gas. Since 93 octane gas is quite a bit more costly, should we burn it, or burn 87 octane and maybe buy some high octane additive to add at each fill-up?

Any suggestions would be appreciated.
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Old 12-06-03, 08:14 AM
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
Go back and get the code# again not the boys interpretation then post back.Has regular maintenance been performed?If the manufacturer specifies 93 that's what you should use.By the time you mix in octane booster the price will be close and you won't know the actual octane level anyhow.
Old 12-06-03, 09:34 AM
darrell McCoy
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As Davo says, use what the book calls for, there is a reason. The system has to try and compensate for the lower ocane. Thats not good. Friend of mine always wanted a caddy, afterwards found out he had to use premium gas only.
Old 12-08-03, 07:03 PM
Join Date: Aug 2003
Posts: 478
See what the owners manual actually says. Some will say something to the effect that if you do not use at least a certain octane fuel you may damage the engine. If this is what it says then it is not wise to use a lower octane fuel.

Some owners manuals will say they recomend a certain octane but they go on to say something similar to what is in the 2002 corvette manual.

"Use premimum unleaded gasoline with a posted octane of 91 or higher for best performance. You may also use .....gasoline rated at 87 octane or higher, but your vehicles acceleration may be slightly reduced. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it is bad enough, you could damage your engine."

This says to me if you do not care about having the best acceleration it is ok to use 87 octane or higher.

The 2002 Acura MDX manual says "Your Acura is designed to operate on premimum unleaded gasoline with a pump octane number of 91 or higher. Use of a lower octane gasoline can cause occasional, metallic knocking noises in the engine and will result in decreased engine performance."

This says to me lower than 91 octane is ok but if I got very much knocking (pinging) I would use the next higher octane.

Notice both of these manuals seem to recomend premimum but neither say it will hurt anything unless you go below 87 for the corvette and then it says you "could" damage the engine.

Octane rating is widely misunderstood. There are all kinds of myths out there such as premimum is better for your engine, it will give you better gas mileage, it will give you more power, it has more detergent in it, etc., etc.. These statements (except the detergent statement) may be true for some vehicles but not for others. They are definatly not true for all vehicles.

Some people put premimum or mid grade in engines designed (as most are) for 87 otane thinking they will gain something. Not true. You are wasting your money unless you have a specific need such as an older engine that has carbon built up to where the compression ratio has been raised and the engine pings because of it.

The basic difference in octanne ratings is the higher the octane rating the SLOWER the fuel burns. When a fuel burns too fast for the conditions with in the cylinder (temperature, compression ratio and copmression pressurethe, load on the engine etc.) the fuel detonates (explodes) and this is the knock or ping that you may or may not hear. The detonation if severe enough for a long enough can cause engine damage.

The knock sensors in modern vehicles will tell the computer to retard the timing when detonation occurs due to low octane rating and I believe in most cases will prevent damage. In years past before computers when the vehicle was timed to take advantage of high octane and in combination with high compression ratios it was much easier to damage an engine up to the point of putting a hole in a piston from using too low an octanne fuel.

Bottom line is read the owners maunal and see exactly what it says not what you think it says and not what your brothers, uncles, sisters, cousins, fathers, neighbor said.

Then decide what is best for you & your car. After all the manufacturer built it so they just might know a little about it.

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