Calling all you "car junkies"

Does it REALLY matter if you put in 87 or 93 octane? My Nissan SUV "recommends it for maximum performance", yet have read it really doesn't matter. Thoughts?

 

The simple answer would be to put in the 87 octane gasoline and drive as you would normally.

http://en.wikipedia.org/wiki/Octane_rating

So when you are driving with the lower octane gasoline check for

1. Knocking
2. Changes in gas milage.
3. Changes in performance when going up hills or pulling trailers.

Then you can make your own decision whether it is worth the extra money.

Gas stations usually have only two storage tanks. When purchasing a "mid-grade" gasoline you are getting a mixture from both the low grade and the high grade. The mixture ratio between the two tanks should result in the desired octane for the product.

You are trusting that the mixture mechanism used by the gas station is accurate. You can imagine how concerned a gas station would be if, perchance, you were getting more lower octaine gasoline while paying for less higher octaine gasoline.

 

The difference between 87 and 93 octane is dependent on the measurement method used.

Chemically 87 Octane Gasoline has the same resistance to detonation as a mixture of 87% iso-octane and 15% n-heptane. 93 Octane Gasoline has the same resistance to detonation as a mixture of 93% iso-octane and 7% n-heptane.

That’s great but how do you measure that?

Well it depends on where you are located.

In most of the world, octane ratings are calculated by using the Research Octane Number system (ROM). ROM is calculated by running different mixtures of gasoline in a testing laboratory where different stresses are applied. The results are compared with different mixtures of iso-octane and n-heptane.

In the United States, we use the (R+M)/2 method, which takes the RON methodology and combines that with the Motor Octane Number (MON), which is a different testing methodology which emphasis testing under greater engine stress. The average of these two numbers is used to calculate the “American” octane rating.

The tricky part is that there is usually a difference between ROM and MON ratings.

This makes “American” octane ratings about 4-5 points lower than “European” octane ratings. American 87 Octane Gasoline is equivalent to 90 Octane in Europe. BTW regular gas in Europe is 95 Octane which would be equivalent to 90 Octane in America.

If your owner’s manual of a European or Japanese car states an Octane rating, check to make sure which method they are basing this on as they can be different.

But truly, the best way is to put a ¼ tank of 87 Octane in your vehicle and see how it likes it. It will let you know. And then you can make your decision.

 

I feel like I see a slight difference in performance, but this could just be my imagination. I'm testing out the difference in gas mileage with my current tank. Should know that in about a week. No knocking sounds of any kind. I've run with 87 octane since I purchased the car in June with no problems. Just curious is all since there is a sticker on the inside of the tank door saying it recommends premium gas. What is the 93 octane REALLY going to do to increase performance? Is the performance "difference" going to be worth the extra $5? All things I need to test out I guess.

 

I would follow Nissan's recommendations .. does the manual mention 87 at all? Usually cars have a knock sensor that will detect any combustion issues and change engine timing to get rid of knocks/etc, but you don't want to chance it have an engine problem.

GO CAPS! =)

 

Is the knocking something I should worry about? I hear it when I'm going up a hill but I don't know if it's just an annoying sound I can live with or if it's my car telling me something is wrong or about to go wrong.

 

Engine knocking (for those who are not familiar with this, it can sound like ticking) is caused by the fuel/air mixture detonating at the wrong time. One cause of knocking is using gas with an octane rating that is too low. Gas that can operate just great in normal driving may knock when the engine is put under stress like going up a hill.

But knocking can be caused by other things wrong.

I would recommend taking your car to a reputable mechanic and having your engine checked for other potential knocking problems. If your mechanic does not examine the engine and just tells you to buy higher octane gasoline, you don’t have a reputable mechanic…..go find one!

If, after a really reputable mechanic checks out your engine and finds nothing wrong, you are faced with a decision.

Repeated knocking will cause excess wear and possibly damage to your engine. If your vehicle only knocks for 5 seconds going up one hill, it may influence your decision as opposed to your engine knocking longer and more often. But generally speaking knocking is a bad thing.

If I had a vehicle that was knocking I would first get it checked out by a reputable mechanic and if there were no problems, I would pay the extra cashola for the next higher grade of gasoline. It may cost you an extra buck or two…three per tank full but that is sure cheaper than getting repair work done on your car. $65 dollars an hour can buy a lot of mid-grade gas.

I have driven many vehicles over my lifetime, some “required” premium gas… none of them ever got a drop of premium gas and all operated just fine.

In my more cynical moments I think that manufactures tell customers that their car “requires” premium gas as a marketing ploy.

 

"Recommends" usually means that you can get away with lower octane. If it is "required", and you use lower grade, you are setting yourself up for blowing a hole in your pistons. On the flip side, if your car says 87, you are wasting money when putting higher grade in. The engine was built for 87 and will perform no better than it would with 87.

Also - When using the lower grade in a "recommends" engine, you may see a reduction in gas mileage as well as power. You may find that the decrease in mileage offsets the savings in using cheaper gas, so it might not be worth it.

 

If you put a lower grade fuel in a car that "requires" a higher grade, couldn't you also void your warranty in the event of a problem?

 

For what it's worth, the guys from Car Talk say that unless your car requires the higher grade you're wasting your money. Here's a link to the information on their website. If you're into cars but haven't listened to their radio show, you should check it out - they're funny!

 

Dear Tom and Ray:

We purchased a '97 Nissan Maxima automatic in January and love it! The owner's manual recommends "unleaded premium gasoline with an octane rating of at least 91." It also says, "If unleaded premium is unavailable, unleaded regular gasoline with an octane rating of at least 87 can be used." Whenever I fill up the car (which is most of the time), I follow the manual's recommendation and use premium gas. But when my husband fills her up, he uses regular gasoline even when premium is available. So my question is, am I spending money needlessly on premium gasoline? And why would Nissan recommend premium gasoline if regular is OK to use? -- JoAnn
Tom: You're doing exactly the right thing, JoAnn.
Ray: This car has a high-compression engine that's designed to run on premium gas. But since there are places where premium gas is not available, and because premium gasolines can vary in octane, most manufacturers, including Nissan, use a "knock sensor" to protect the engine.
Tom: The knock sensor detects -- that's right -- "knocking" (also known as "pre-ignition" or "pinging")! Knocking is bad for the engine, and it often results from using lower-than-recommended-octane fuel. So when your cheapskate husband puts regular unleaded in the Maxima, the knock sensor kicks into action and retards the ignition timing to protect the engine.
Ray: Retarding the timing prevents the knocking, but it also reduces the engine's power, decreases fuel economy, probably increases the emissions, and may lead to a buildup of residue on the valves. So it's not an ideal situation. It won't hurt the engine if you use regular gas occasionally, but it prevents the engine from performing at the specifications at which it was designed to perform.
Tom: So I'd either take away your husband's keys, or increase his allowance by a few bucks a month so he can afford to buy premium. And if he's unhappy about having to spend the extra money, remind him that a car's fuel requirement (which can add many hundreds of dollars to the cost of owning a car over the years) is one of the things you should find out about before you put down your deposit.

 

If your car's manual recommends regular gas, you don't benefit from premium:

Dear Tom and Ray:

We really enjoy your column! Our car is a 1992 Honda Accord. Our service man tells us that we would get better mileage as well as a cleaner engine if we use unleaded premium gas instead of the recommended -- and cheaper -- plain unleaded. We do not have money to waste. What do you say? -- George
Tom: Well, if you had money to waste, I'd say sure, use premium unleaded!
Ray: A waste of your money is ALL you'll get from premium fuel in your car, George. Some cars require premium gasoline because they have high compression ratios and require the higher octane fuel to prevent pinging. But yours isn't one of those cars.
Tom: You won't get measurably better mileage, you won't get a cleaner engine (because almost all regular unleaded has the same detergents found in premium gasolines), and your car will create more pollution.
Ray: Sounds like a deal, huh?
Tom: So stick with the manufacturer's recommendation for octane. No more, no less. And save your hard-earned money for luxuries you'll be able to really enjoy-- like crushed Corinthian seat covers.

 

Used to listen to Car Talk all the time with my father when growing up. Those guys are GREAT!!! Are they still around?

 

Yup! We listen at 10am on Saturdays on 88.5. I think they're also on Sirius/XM radio.

 

I listen to Car Talk on Saturday mornings, as well. T8erman always just walks in and shakes his head. I love them!!

 

The way I look at this argument is today, 87 octane is $2.19 and 93 octane is 2.44 at the exxon by home depot, the difference of 25 cents per gallon, my car, which also requires 91+ octane takes 17 gallons to fill up. We're talking a difference of $4.25 per fill up between 87 and 93 octane. I'd rather pay $4.25 more per fill up, than to risk having my motor knock which over time can lead to more problems... Just dont eat Mickey deez big mac meal for one day out of the week and your good