Dear Tom and Ray:

I have a 2004 infiniti G35 coupe. Infiniti advises that you should put premium gas,at least 93 octane. I have a friend of mine who owns a 2005 TL Acura. His vehicle requires premium gas as well. He was told by a mechanic at Accura that he could use middle grade fuel, 89 octane, and it would be no problem. He has been using the 89 octane for nearly 6 months with no issues. He advised me that I should do the same, and there should be no issues. He also stated that the new high tech engines have a computer system that will adjust with the lower octane, and the engine will adjust. He also stated that if I used a good grade of fuel injector cleaner every 3 months or so (chevron) this would keep the injectors clean with the reduced octane level. I am hesitant to do this, do you agree or disagree? With the rise in gas prices, I think many people are looking to save a few bucks any way they can. I look forward to your opinion, thanks. Kevin

It’s a gamble: save a few dollars today, and chance losing thousands (in repairs) tomorrow. Are you that much of a gambler?
It’s true that the engine control computer can make adjustments for lower octane gasoline; but, there’s a caveat. The caveat is that the detection (sensors), control (computer), or execution (actuators) might take a nap. Then, severe damage to the engine can happen.
You’ll have people who’ll tell you that the system never fails. Do you want to gamble?

The engine computer, along with help from the EGR system and the knock sensor, can compensate for lower octane fuel up to a point.
Your friend is incorrect about reduced octane rating having anything at all to do with the cleanliness of the fuel injectors. Your friend is also wasting money by using a cleaner every 3 months.

The key point is being aware of any pre-ignition rattle that may occur. A rattle could be caused by using lower octane fuel and this can be damaging to an engine over the long run, or short run in extreme cases. A rattle can also be caused by a faulty or dirty EGR system, a faulty knock sensor, and in many vehicles, improper setting of the ignition timing. The latter is only applicable to distributor equipped cars so this does not apply to either of you.

If there is no pre-ignition rattle and both performance/mileage stay about the same then there should be no problem.
Ninety-one octane is recommended for my Lincoln and it’s been on a steady diet of 87 for the last 140k miles with zero problems. No drop-off in mileage or performance and since I’m pretty nit-picky on the maintenance I pull the spark plugs every 10-15k miles for inspection with replacement of the plugs at about 30-40 miles.
Inspection of plug tips is the best way of knowing what is going on inside the engine and the plug tips say everything is ducky. JMHO anyway.

(Matter of fact, on trips to Colorado I’ve run 85 octane and pulled steep mountain grades with zero problems or loss of mileage.)

You bought a car just like a well financed person and now you’re thinking of buying cheap fuel. It is simpler just to read the owner’s manual. It says premium fuel. Use it and avoid trouble. If you want to save money, there are a lot of better methods.

87 octane is 20 cents cheaper and 89 is 10 cents cheaper than 93. if you have a 20 gallon tank that you let run dry before you fill it up, you’re only saving $4/$2 per tank fillup. You will also get reduced performance and reduced fuel economy with the 87/89 octane. You bought a performance vehicle, care for it as such.

The octane level has absolutely zero to do with injector cleanliness. All gasolines already contain all the detergent additives you need.

And, as OK said, your engine can only compensate to a point and as everyone has said there may be a performance tradeoff.

So, your friend saves $2 a tank in gasoline and then buys a $10 unnecessary fuel additive to compensate for the tradeoff that he thinks he’s making but isn’t (the tradoff is in performance, not injector cleanliness)? Interesting.

Use what your owner’s manual recommends. The fellas that wrote that know your car better than your friend does. Vary from that at your own peril.

I guess that you’re warranty has expired. If so, you don’t risk voiding the warranty.

It seems to me that Nissan mandates the use of 93 octane because they designed the car to run best on it. I don’t think that any of us are more expert on the Infiniti than Nissan is. If you drive 15,000 miles per year and get 20 MPG, you save $75 for a differential of 10-cents per gallon. Is it worth $75 a year to switch to 89 octane or $150 to switch to 87 octane?