[Myrddin]

It's a function of what the manufacturer recommends. If you choose an octane grade that is lower than the manufacturers recommendation, you may end up with pre-ignition aka pinging. This is caused by a more volatile combustion mixture igniting due to compression...before the spark plug does the job. It can destroy your engine. Higher compression engines require higher octane.

I live at a higher altitude (4600 ft). Our gas stations offer 85 octane. In San Diego (sea level), the lowest octane offered is 87. Buying a lower octane than required can result in engine damage. Buying a higher grade than required is a waste of money.

[Gilbo_3]

Ditto to #2 & #3. I would also recommend that you stay current on the maintenance as you say you have. keeping the fluids & filters {ALL OF THEM!!! } clean is the best bet for longevity ive seen. Use the Lowest recommended octane that doesn't cause pinging and throw in a bottle of techron on occasion for extra shot of injector cleaning. Hope it helps ease your mind...

[Rain-maker]

If you are running too low of an octane for your motor, you will get
pinging. Pinging in its extreme form is also known as detonation. The
fuel/air mixture is igniting all at once and exploding instead of igniting
as a flame wave. The resultant "bang" is very hard on the pistons, head,
rods, and cranks. I've seen bent rods, cracked heads, pounded-out crank
bearings, cracked piston skirts, chainsawed crankcases, and thrown rods.

 

The only time higher octane is of any benefit is if the car pings on the

recommended grade, the timing is advanced, compression is higher
than stock, or the car has forced induction.

 

Newer cars  generally wont  knock or ping because they have

knock sensors that can compensate ignition timing for lower octane fuel.

[gonzo]

"...I travel over the coast mountain range to get to Portland on a regular basis. Steep up and down to get over..."

Todays' engines with fuel-injection will digest just about anything from 83 to 97 octane. Try it out with each grade, and use the grade that doesn't ping.

More importantly, after 3000 miles, add a quart of a Teflon-lubricant like Slick-50, and change yer oil every 3000 miles. Add the Teflon-lubricant every 30,000 miles thereafter. The engine will run for 300,000 miles, and never smoke, unless you haul elephants.

Don't forget the brakes!...........FRegards

[goodieD]

I would like to add here that you have to be very careful, because many unscrupulous gas stations have the exact same gas under different grades. You may be paying for premium and getting regular.

[Uncle Miltie]

Since the war is over gas, I'd stick with VX.

</sarcasm>

[Elsie]

I have two G-30, 1 ton Chevy vans (350 engines - automatics) that run on 87 octane, bought at the cheapest place available.

The '77 has over 304,000 miles on it, does not burn oil. I replaced the cam in it 15 years ago.

The '90 just rolled over 198,000 yesterday, does not burn oil.

Though many ACCESSORIES have croaked in this time, but the engines are strong!


What more could you ask for?

[Extremely Extreme Extremist]

Premium gas is a waste of money, unless you have a bucket of a car (think mid-80s Chevy Caprice Classics) that runs better from higher octane.

[1Old Pro]

87 Octane should be fine unless othewise recommended from the manufacturer, which I doubt.

[Crusher138]

Guy who sold me my Audi (which recommends you use premium) told me that the computer was good enough to handle any grade of gas and that they had an unpublished report of A4's running on a variety of highly flamable liquids, i.e. alcohol, just fine on a temporary basis.

Don't know if I believe him or not, but the couple of occasions I have had to put 87 octane in my car I have noticed no degradation of performance.

[ez]

I ran a spreadsheet one time and I entered all my miles, gallons, and price of every tankful for about two mos, and if you take it down to "cost to drive one mile", there is virtually no difference between Regular and Premium, due to slightly increased mpg's for Premium.

Therefore, one should follow manufacturers recommendations without reservation.

I run 87 in my Frontier cause the book calls for it, but I ran 93 in my 240SX with the same engine. Go figure...

[jiggyboy]

A few minor points not already covered:

- Check in your owner's manual for the type of gas that is recommended for your car. They will come right out and tell you that it should be, for example, 87. Re your #14, different cars come with different recommendations. You're not giving your car a yummy treat if 87 is recommended and you give it 89 or 91.

- 3,000 miles between oil changes is the rule of thumb; I have done very well indeed by going by the recommendation for my particular car, which has been 7,500 miles for two different cars. It saves me a marginal amount of money and time. This might also be in your owner's manual, might not, but would definitely be found in a "Haynes" repair manual that you could get at most auto parts stores for like $15.

- I have also done very well with cheap, no-name gas vs name-brand gas. Mileage is the same, engine life can't be beat (210K and 150K so far).

- I have heard what sounds like a lot of BS, mostly from auto dealers, that Arco gas (it contains some methanol) beats up the rubber in the engines of new cars. This, based on a one-car sample of 75K miles, is demonstrably BS.

- "All filters" includes the air filter, the fuel filter (sometimes 2), PCV valve, etc.

- Check your radiator, tires, and oil about the time you fill your car with gas. You'll determine pretty quickly whether you've got a leak in any of those systems.

[Burlem]

I listen to Dr. bill Wattenberg on week-ends. His partial resume is: Research Scientist, Professor of Sscience, Consultant to Livermore National Lab, Staff member of physics division of nuclear weapon design.
I tell you this so you know he is of crdibility. He said that if you buy the high octane you are wasting money. There ARE some high performance cars that need this gas, but the average persons car can do well on regular. I have a 96 Crown Victoria, the book susggested the medium grade, when I heard Dr. W, give this advice, i switched and had no problems.
You can try the lower grade, he said if it pings too mcu then go back but in the majority of cases the car will be fine and you will have more money in your pocket.

[Johnny Gage]

One thing I recently learned about reg/prem gas.

According to several 'small egine' dealers:

If the lower grade gasolines have ethanol in them (like in Minn.) you will want to run premium gas in all your small engines. (mower/chain saws/atvs etc.)

The reason is that the ethanol can cause damage to the alloys used to manufacture the blocks/pistons etc.

Just my 2.9 cents. As with things like this YMMV.

[WFTR]

As others have said, "octane" is a measure of how quickly the gasoline burns. Ideally, you want an even burn and even expansion in the chamber for the entire piston stroke. If your gasoline burns too quickly (has too low an octane), it finishes burning and expanding while piston is still moving towards its most open position. The expansion from other cylinders must then force this piston to complete its movement. If your gasoline burns too slowly (has too high an octane) then you are losing fuel value to the exhaust.

Generally, higher octane is attained with heavier hydrocarbon molecules and with branched molecules. Refineries have special units to produce these molecules from smaller, lower-value molecules. Sometimes, a higher octane gasoline is better in the summer because it will not evaporate from the tank as easily. Likewise, some people have used lower octane gasolines in the winter because the smaller molecules flow better under cold conditions. In many states, the government forces refineries to make some of these seasonal adjustments within an octane rating.

The difference between gasoline brands is typically only a difference in additives. Naphtha is naphtha is naphtha regardless of who refines it from crude. The secret is in what they add.

WFTR
Bill

[azhenfud]

Really - economics make the difference negligible for me. I use the high octane.

My case is(was) like this:

16 gal tank @ 18.125 mpg x 1.749/gal regular @ 290 mi range/tank = 0.0965 cents/mile

16 gal tank @ 19.755 mpg x 1.949/gal premium @ 312 mi range/tank = 0.0986 cents/mile

I'm to the opinion the octane/mpg is calibrated by the oil companies to net the same - regardless. But, you do the math on your own experience and see....

[Petronski]

In general, you should use the lowest octane which the manufacturer recommends. If you have engine knock, you should try the next higher octane level until the knock goes away. Then continue to use that octane level.

These 'premium' 93 octane fuels offer no benefit to an engine not tuned to take advantage of them.

[HairOfTheDog]

If you vehicle runs well on the regular, go for it.... My truck pings on regular gas.... I always by the middle gas (at least 89 octane)

[Jhoffa_]

The posts about it not mattering much on your trip to the post office are correct.. It really donesn't matter to the average driver.

In the past a high octane rating allowed you to run higher compression ratio's and advance your ignotion timing, resulting in more power, improved efficency and better throttle response.

That was when the timing curve was fixed and controlled with centrifugal force and vacuum canisters however.

As it stands now, the computer in your car will detect engine "knock" (pre-ignition) and will alter the ignition timing to compensate, (sometimes even on a per-cylinder basis) as "knock" is harmful if it continues for extended periods (read, REALLY, REALLY, insanely LONG periods.) of time.

It's no big deal, run whatever you want in it for your trips to the grocery store.

[peteram]

Several years ago, a friend of mine told me that he had heard (from Clark Howard, I believe) that there was NO difference in octane ratings. That one grade was just as good as another.

So, after using premium (93 octane) in my Firebird since the day I bought it brand new, I decided to step down to the lowest grade (87 octane). Within 3 weeks, I had to take the car in to have the fuel injectors cleaned out - something I never had to do before through other tune-ups. (these cleanings are not cheap,either)

Needless to say, I went back to premium gas, no matter the price.