Is Premium gas really needed?

Hi all,

I just purchased a 1997 Nissan Maxima SE and have read lots of talk about using premium gas. So, is premium gas really needed or is it just a preference. What kinds of symptons should I look out for if I use the regular 87 Unleaded gas? I'v'e had the car for 1 week and am getting ready to gas her up, so I'm trying to get a feel as to what gas I should use.

Thanks in advance

Old Geezer

Yes, it is necessary. Engines like the VQ30DE that powers the Maxima are high compression engines; the Air/Fuel mixture is compressed to 11 atmospheres in the firing chamber before it's detonated by the spark plug, IIRC.

If you'll recall back to high school chemistry, when you compress a gas, it becomes more volatile and combusts at lower temperatures. This is important because the more your compress the A/F mixture in the firing chamber, the easier it is for the radiant heat from the engine block to detonate the mixture. This is problematic because it drives the piston down before it (and the crankshaft) are ready. This is knock.

Premium gas is of a higher octane than regular gas. Contrary to popular belief, higher octane does not always result in better performance (from a horsepower standpoint). Octane retards ignition so higher octane fuels require more heat to detonate, thereby lowering the chances of predetonation. That's why people who are running nitrous oxide or forced induction run 93+ octane fuel.

The onboard computer can do nothing to overcome the lack of octane besides retard the timing advance. On the Maxima, if the knock sensor trips, the ECU automatically retards the timing and you lose 20% of total power throughout the entire RPM range. I'd rather pay the extra dime per gallon and get the full potential of the car, even if I'm always cruising at 2,000rpms.

If the knock sensor trips, your car will be sluggish, especially when you floor it. Run the premium, it's worth it in the long run.

~THT

thanx dude, i was putting in 87, and my transmission was making noises, when i put it in drive, you could hear it change, i put 93 in, and no more noises

If you'll recall back to high school chemistry,
~THT




I don't recall back to highschool anything. lol

does that apply for the older maximas?? cuz i've been runnin 87 octane n im juss curious

The principles apply however, older engines such as the VG have different compression levels. If the ratio is lower, you can run lower octane fuel.

~THT

Thanks THT!

I went ahead and put in the new Shell V-Power gasoline. I figured it will be approx $3 more to fill up my tank.

And believe me, it'll be worth it. Good choice!

~THT

i only put plus cause i can't afford getting supreme all the time.

What would happen if I put 100 octane fuel in my 97 Max? I haven't done it, but was curious as to what it would do. The engine is stock.

I have been putting that V power in from shell.. Car seems to like it... I think I have used both 94 octane and 93 from shell.. is that possible?

100 octane would result in less chance of predetonation, nothing else.

~THT

THT

It sounds like you know what your talking about, that was a great eplination of regular to premium. Is there a actual knock or ping noise that you would hear? I've used regular some times just to see if it would shut of my SEL. For some reason it has, "the code that autozone pulled was something about the CAT Po420 I think" Anyway when I use regular I notice that if I am light on the gas and approach a hill etc. the engine hesitates with a ping type of noise. But if I'm on the gas I never have a problem the car runs fine Regular or Premium. My only concern is whether this can cause future problems like a bad oxygen sensor or something like that. I would appreciate your input.

Yep, when there's knock, you'll here a metallic "ping" sound. Our knock sensors have a crystal piezo element (I think that's what it's called...) that is tuned to respond to that specific sound frequency so the ECU knows when knock has occurred. It's not very loud so if you have your radio playing, you may not hear it.

As for causing other problems, switching gas grades can gum up your cat IF you're switching with an ethanol blend. And usually, a bad O2 sensor will cause the knock sensor code when in reality, your car's not knocking.

~THT

I don't recall back to highschool anything. lol

lol and i never took chemistry...lol

I have used 89 octane for long trips, mostly highway miles, and did not notice anything unusual. When I do burn the 89 octane I add it to my tank when it still has half a tank of the 93 octane. I've never burned the 87 octane. :wink:

THT - I like the explanation. Thanks. I was wondering if there is any negative effect of running a consistant 93 octane fuel containg a small percentage of Ethanol. I think Sunoco advertizes 10% ethanol in their selections...
MSC

Nope. Just don't switch between blends and non-blends otherwise you'll gum up your cat.

~THT

I agree. Stick to one grade of gas. I have always used Premium on my 1996 Maxima. I get upto 33 mpg on the highway and 24 mpg in a mix of city (45%) and highway (55%) driving. Plus the car continues to have excellent passing and pickup power. I might have used Regular or Special gas a couple of times (when the gas station ran out of Premium). Last Friday, I decided to use Special because of all the rising fuel costs. On Monday, the check engine light came on and Midas told me it was the upstream oxygen sensor acting up. Only last month, I had replaced all 3 exhaust pipes, downstream oxygen sensor, muffler and catalytic converter for $1140. But since my car's performance and mileage seem fine, I am going to just follow the suggestion from another thread (go to http://www.automotiveforums.com/vbulletin/showthread.php?t=232932&highlight=oxygen+sensor and look for a post by gregory4041), run the car for a few days and see if the check engine light goes away.

On MAXIMAs/I30,I35 91 octane is recommmmmended (nissan is a tq base Vehicle) and to prolong the longitivity of the ENGINE. But check this out... you could insert 87octane w/ 10% Ethanol; dyno both respectively and oddly the second fuel mixture will output more Tq's and Hp's then 93 octane.

Got a dyno sheet of a VQ30 to prove that?

~THT

Greetings,
Just got back from the NY Auto Show. During the trip I put 360 miles on my '02 I35. I used 89 octane for the entire trip and the car ran fine. I've been using 89 octane for several months with no problem. I talked with an Infiniti service tech and asked him if using 89 octane instead of 92 octane could damage the O2 sensors or any other emissions equipment. He told me the 89 octane was okay to use. I have to agree with the service guy. The car does not ping under hard acceleration and that would be an early warning that the octane was too low. I'm staying with 89 octane for now. I'll let you folks know if I have problems. By the way, I use "name brand" gas like Gulf, Citgo or Sunoco.
Regards,
Shortimer

use at least 91 :)