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Which grade of Gasoline to use ?

I use the 87 grade on my corolla, and the 93 grade
once a month to keep the engine clean(so I was
told), although I am not sure what is actually
cleaned ? Any thoughts on this.
«1345

Comments

  • guitarzanguitarzan OhioPosts: 804
    Sometimes higher octanes contain more detergents, which is what you're probably paying for. Personally, I don't think a periodic high octane fill will clean anything. It could actually cause more deposits, since the engine was not designed for that octane. Doubtful, but theoretically possible.

    To clean out carbon deposits, take the car on a
    30-40 minute highway drive. The heat the engine generates acts as a very powerful cleaning agent. If you do this daily, all the better.

    To clean deposits from the fuel tank, fuel line,
    and to eat out any water in the bottom of the tank, periodically use a fuel system cleaner. Make sure and use it on a full tank. It is very caustic and in full concentration could actually damage the fuel filter, and any exposed plastic parts.

    I'll put this topic in my placemarks, and ignore the misspelled one that I initially responded to.
  • my husband insists on always using premium gasoline in our 1980 oldsmobile (we bought it in the fall). is this absolutely necessary?

    thanks,
    Andrea.
  • nope, not at all. Just wasting money. Although I'm sure you won't be able to get him to change. Actually, it wasn't necessary when you bought the vehicle to use premium, but you might need at least the middle grade now. Because your vehicle is 19 years old, it probably has high mileage and may now be more subject to pinging with the 87 octane (low grade) that it was probably designed for.
  • guitarzanguitarzan OhioPosts: 804
    I had a 1980 Delta 88 with the Olds v-8, and 80k+ miles. It required high octane, or it would ping severely. It is hard to say what is most cost efficient. Some pinging is okay. A severe and/or constant ping may actually shorten the life of some engine parts. Also, the mileage was significantly better with the high octane, leading me to believe it ran too hot with 87 octane. The Chevy v-8 offered, I believe, is a little less prone to pinging, valve problems, and the such. If you have the v-6, heck if I know :)
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    I always tell people to use the lowest grade of fuel that the engine will happily accept. You don't do any good whatsoever putting premium fuel in an engine that wasn't designed for it...it's not any better or more powerful...the octane rating relates to the rate and evenness of the burn, and some engines are finicky about that.
    Nor is it related to the size of the engine or the horsepower what type of fuel you might need. You really need to go by what the manufacturer says and how your cars really runs...pinging should be avoided at all costs, unless it is brief and minor...that clinking noise is your internal engine parts rattling around!
  • if you want a higher octane fuel. go to your local parts store and buy it. a small bottle of 102 will
    go a lot farther than a tank full of $ 100 gas will
    add it when you want that extra couple of horses
    also that pinging can be taken care of by timing
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Well, maybe, maybe not. Some of those products do work, and thanks for thinking of that, smithc, but I've seen tests that show quite convincingly that many don't do diddly...also, given the small amount of octane boost you get from a $5 can, it's hard to justify the cost over just buying the right gas.(e.g., if premium fuel is 20 cents more per gallon, and your tank is 15 gal, that's only $3 more, and you get 4 or 5 more octane points, which no can of whatever is going to do.)
    True, retarding the timing (you can only do that on older cars safely--the new cars do it for you automatically)will cure the pinging, but also cut way down on your power.
  • KCRamKCRam Mt. Arlington NJPosts: 3,516
    an old co-worker of mine used to use premium religiously - he felt regular and plus were watered down version of the best. Until the fuel prices skyrocketed in 1990 from the Gulf War. And here in NJ, regular was averaging $1.40, premium $1.65. So to save money, he bit the bullet and bought regular. You guessed it - the car ran exactly the same. He never bothered with premium again.
  • edw1edw1 Posts: 2
    I always use a higher octane in my 5.9 gas engine whenever I am pulling my 32 foot fifth-wheel and it does help in many ways. Usually I only run 87 octane when in the normal driving mode.
  • edw1edw1 Posts: 2
    I always use a higher octane in my 5.9 gas engine whenever I am pulling my 32 foot fifth-wheel and it does help in many ways. Usually I only run 87 octane when in the normal driving mode.
  • wow, what great answers to my question. I'll print them out and show them to my husband and see if he'll change his mind. he loves this car and I think he thinks he's "babying" by putting the more expensive gas into it.

    thanks,
    Andrea.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Hmmm...curious, Edw1....what benefits do you notice in your truck from using premium?
  • GischpelGischpel Posts: 133
    I was told that gasoline is "cut" differently in the winter (more of something -- kerosene? in the gas) and because of that the higher grades would give better performance. We usually run 89 in the winter in my wife's car and 87 is the summer. My truck runs 87 year round, so I am not sure what that says...

    Terry
  • KCRamKCRam Mt. Arlington NJPosts: 3,516
    Diesel adds kerosene in the winter, not gasoline. Gasoline tends to have extra oxygen in the winter (hence "oxygenated gasoline"). In either case, winterized fuel is less efficient (less complete combustion), and will cost you anywhere from 1 to 5 mpg. Certain cars will run better on a higher octane gasoline in the winter depending on how their computer is programmed.
  • royallenroyallen Posts: 227
    My understanding is that separate from oxygen content, winter gasoline will form vapor at a lower temperature than summer formula. This variable does not change octane but helps avoid flooding in winter and avoid vapor lock in summer. It becomes important if fuel stored in the shed in summer goes into a snow blower or a winter blend is used in summer.

    On the topic of oxygenation, power is reduced not because of incomplete combustion, since the (however modest) purpose of oxygenation is to make combustion more complete and improve emission quality, lowering CO. The power loss is due to replacing carbon and hydrogen, the fuel, with oxygen. In contrast, pumping in the oxygen with a turbocharger from an external source readily increases power.
  • guitarzanguitarzan OhioPosts: 804
    Funny you say that. I just talked to a buddy today who has a 1984 Turbo Coupe T-bird. He uses 89 octane in warm weather, but told me he gets detonation with that octane in the winter, thus he switches to 92. I learned this 2x today :)
  • I believe I read in my owners manual that if your car doesn't run properly on the octane it was designed for, it has a problem which should not be properly cured by increasing octane. Older cars, you would retard the timing in this situation. Somewhat newer cars like my '91 Mustang you would disable the spark advance, then with a timing light you could adjust/set the static timing. I believe it had a knock sensor, but I could still advance the timing too far and it would knock. If I ran high octane, I could get more power running more spark advance. Theoretically, a car with a knock sensor can advance the spark for more power automatically if it does not detect knocking. That would be the benefit of paying for premium at the pump. But more octane than you need to prevent knocking, whatever your power level is wasteful.
  • GischpelGischpel Posts: 133
    Thanks for the update on the gasoline. I knew it was somehow different in the winter, but couldn't recall the details.

    Terry
  • KCRamKCRam Mt. Arlington NJPosts: 3,516
    royallen,

    Technically, we're both right. You are correct that the power loss comes from a lower percentage of hydrogen and carbon. But because of that "unbalance" (more oxygen than the engine would like), the combustion process is not as complete as it could be. A non-turbo engine running oxygas has no idea how to compensate for the extra oxygen, and thus has trouble completely burning it. The extra oxygen, in theory, bonds to the extra carbon monoxide to make carbon dioxide.

    Turbos thrive with the extra air pressure because the fuel is also increased to match. This is why turbos are generally made from 4 and 6 cylinder engines - they are attempting to achieve V8 power. Putting oxygas in a turbo multiplies the problem, because again, there's more oxygen than the engine wants, under boost or not.

    New Jersey has been fighting the federal EPA for years now, claiming oxygas does not reduce emissions at all, and because of the reduced mpg, forces motorists to buy fuel at a quicker pace, wasting money.

    Since I have a diesel, I have to deal with winterized diesel-2. The kerosene keeps the fuel from gelling and waxing - you know when you leave a frying pan on the stove overnight and the grease turns into a thick white gob? Diesel fuel, being an oil, does the same thing during extreme cold temperatures. The kerosene acts as an anti-freeze to delay this gelling, but at the expense of the fuel's overall combustibility. I lose 2-3 mpg on winter diesel compared to straight diesel in the spring and summer.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Here's an interesting quote on the subject:

    " A 1990 study by Public Citizen, A Washington DC consumer advocacy organization, found that while 20% of gasoline sold in premium, only 3% of cars actually need it. Premium therefore, cannot improve performance on 97% of all cars, and it doesn't clean engines any better since virtually all gasoline now contains the same detergents in the same concentrations. In 1991, the FTC ordered Sunoco to stop advertising its 93.4 and 94 octane gas as superior in providing engine power and acceleration because the company could not substantiate their claims." THE CONSUMER BIBLE

    Another one:

    "How widespread is octane fraud? Five separate investigations done since 1990 have found up to an 18% octane mislabeling rate (selling regular as premium). In 1990, the New York City Department of Consumer AFfairs found a 16% rate; by 1993, stepped-up enforcement agains gas cheats had reduced it to 4%"

    ...(hey, that's still 1 out or 25 gas stations, and that's WITH strict enforcement). Draw your own conclusions next time you fill up...
  • KCRamKCRam Mt. Arlington NJPosts: 3,516
    Shift,

    Exxon was sued a few years back by the feds for pretty much the same thing. The settlement involved Exxon to place electronic and print ads stating that premiunm is only for vehicles that require it, and that regular and plus had the same additives as premium.

    Most gasoline ads around here still tout premium grade, but carefully say "for engines that need it or drivers that demand it". That last part of course for thoae who don't care how much money they throw away...
  • Again, there is some extra power that can be attained, under the proper circumstance of advancing the spark timing. But without the spark advance, the extra octane is wasted. It also should be possible in some cases to reduce octane to a lower grade on a high performance engine by retarding spark advance, at the cost of ultimate power.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Yes,true, but that "power" is not in the fuel...high octane just burns better, but doesn't have more inherent energy...anyway, on most modern cars the timing is optimised for you, you can't touch it; on older cars, you can get too frisky with the timing and burn a hole right through a piston.
  • I did notice more power, smoother shift and less noise from the engine of an Acura Integra 94 when I put in 91 instead of 87... I only tried to use 91 when it's on sale. (for the price of 89 or cheaper than 89) I prefer to use Mobil.
  • guitarzanguitarzan OhioPosts: 804
    Which model? Is that the GSR? I had a '93 base model, and couldn't find any difference in power between 87 and 94 octane. The VTEC model probably does take advantage of high octane.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    Again, depends on what it's built for...if the engine is supposed to run on regular octane, it should make no difference at all...it's hard to say what we really notice when we do these experiments...I would swear my car runs better after I wash it, but really now.....
  • volfyvolfy Posts: 274
    Quadrunner500 is right. The answer boils down to whether your car has knock sensor(s) or not. An engine equipped with one (or more) will advance the ignition timing to just shy of knocking to maximize power, and thus will benefit from a higher octane gasoline.

    On engines without knock sensor(s), the manufacturer generally sets the timing map conservatively enough to run fine on the lowest octane commonly sold. However, without the close-loop feedback from the knock-sensor(s), the controller can only operate open-loop, that is, advance the ignition timing according to a preprogrammed ignition map. As such, the controller can't "see" the higher octane gasoline and thus won't take advantage of it.

    Aftermarket chips generally have more aggressive timing maps, combined with more generous fuel metering, in order to make more power. And usually, they require premium gas.

    All bets are off, if you don't take care of your engine. Carbon build-up on piston crowns can raise the compression ratio enough to cause premature engine knock. Likewise, carbon build-up on intake valve can soak up the atomized fuel on cold starts enough to make the engine idle rough.
  • arazaraz Posts: 27
    I have noticed a difference in MPG between regular and premium in a Dodge pick-up. The explanation I got sounds almost the same as yours. This phenom is more noticeable when towing.
  • volfyvolfy Posts: 274
    araz,

    Knock sensor or not, an engine will be more prone to knock or pinging under high load conditions such as full throttle or towing a heavy load, or high temperature. Higher octane essentially makes the fuel mixture burn slower thus allowing the thin layer of air ahead of the flame front a better chance at insulating the piston crown from melting.

    If your truck has know sensor(s), the ignition timing may be retarded so much with regular unleaded under high load conditions to cause you to step on the pedal more and more to get the performance you require. Otherwise, the mpg shouldn't be all that different.
  • spokanespokane Posts: 514
    Volfy makes a very good point that an engine which performs well on regular fuel, and is not equipped with a knock sensor, cannot "see" the higher octane and therefore cannot take advantage of it. Premium fuel in such engine is very likely to be a waste of money.

    In order to evaluate fuel-cost economics, I once set the time on a 390 CID Ford (during the era of leaded fuel and no EGR valves) as high as pre-ignition would permit on regular fuel and drove for ~5000 miles while keeping a careful record of fuel consumption. Keeping things such as season and driving pattern unchanged as much as possible, I began using premium fuel, reset the time and repeated the evaluation. In this case, the premium fuel cost 13% more but I managed 19% greater mileage per gallon. The reverse would be true for many cars, of course. I don't suggest that others repeat this with today's knock-sensor engines but I cite this because it seems seldom that anyone attempts an objective evaluation of "octane economics."
This discussion has been closed.