Which Grade of Fuel Do You Use?

[Joe Dragon]

Re: Which Grade of Fuel Do You Use?

I use regular octane in my Avalon because that's what Toyota recommends. The only thing is in the winter I have to use ethanol infused gas (by government decree here in the People's Republic of Colorado), but starting in April I'm back to buying non-ethanol, despite it being 25 cents more; it pays for itself in significantly better gas mileage compared to E85.

[panicdog]

Re: Which Grade of Fuel Do You Use?

It all depends on your engine's compression ratio. Higher compression engines need higher octane fuel to avoid autoignition. If you are not getting autoignition with the fuel grade you are using, then moving up to a higher octane is simply a waste of money.

It's not as simple as saying higher octane is better or worse. It's more of a question of whether or not it is needed for your engine.

I follow my car's manual. I work in Saudi Arabia and we only have 2 ratings for gasoline which is the 91 and 95.

I use the 91 because my jeep's manual says so, plus 91 is dirt cheap here at 0.12 usd/liter (cheaper than water).

[aris]

Re: Which Grade of Fuel Do You Use?

87 octane

[Farmer]

Re: Which Grade of Fuel Do You Use?

Nothing less than 91.

[jezz12]

Re: Which Grade of Fuel Do You Use?

in my country cheapest octane is 95...
i pump non other than exxon mobil as it comes with addictive...

[beamer]

Re: Which Grade of Fuel Do You Use?

both my vehicles take premium. i use 91 with no ethanol and just foind a station that has 93 no ethanol. it helped milage alot. ethanol kills milage. i hate the stuff. and if we get worse milage on corn and burn through more whats the point.

[Wilhelm]

Re: Which Grade of Fuel Do You Use?

Only use regular these days, but will occasionally put a tank of Shell Premium in the Infiniti. I can't tell a difference unless I put my foot to the floor and even that may be in my head.

You may or may not be able to tell the difference, but there is definitely a difference. And the occasional tank of premium isn't going to resolve the reduction in power and may therefore just be a waste of money.

The higher the octane rating, the less chance of know (detonation). As a general rule, for the purposes of discussing whether it is "OK" to use regular gas when the manufacturer recommends premium, detonation is more likely to occur in high compression engine, on a high ambient temperature (like a 100 degree day), and load (e.g., sudden acceleration, carrying a heavy load of passengers/luggage, going uphill.


When a manufacturer recommends regular in a particular model, using premium won't hurt anything, but it is a waste of money. If all you need is regular to run at designed efficiency, anything more contributes nothing to engine performance.


When a manufacturer recommends premium in a particular model, it can and will run with regular. In this situation, if you put in regular gas, the car will continue to run normally and I doubt anyone will be able to tell the difference. However, once you start pressing down on the accelerator, the knock sensor will signal the PCM that detonation is occuring and ignition timing will be retarded until the knocking stops. As a result of the timing retardation, engine torque is reduced. Again, the difference will probably not even be noticed, but it probably affect fuel economy.


The process of retardation of the ignition timing because of the detection of detonation by knock sensor is an adaptation, i.e., the PCM will "learn" that regular is being used and keep the ignition timing retarded to avoid detonation.


The adaptation can be cleared or reset if you have a scanner (not an OBDII scanner/code reader, but a "real" one, i.e., similar in scope and function to one a dealership service department is likely to use. Most people do not have a means of quickly resetting the adaptation, and rely on the car computer to reset the ignition timing on its own. Thus if you start using premium gasoline, the PCM will gradually permit the ignition timing to advance. It may take several tanks of premium to restore normal timing, to regain optimum fuel efficiency.


So if you use regular when the manufacturer recommends premium, the timing will retard, available torque will decrease and merely running the occaisional tank of premium will pretty much have no affect in restoring engine power and fuel efficiency. Real world example: Suppose I have late model BMW, 10.7:1 compression ratio, manufacture recommends premium fuel and I drive around on regular. Within a short while the engine (specifically the ignition timing) will adapt. I will probably only notice when merging onto a freeway or pressing down on the accelerator to change lanes. The same amount of power won't be there. I'll have to give it more gas (which will lower the mpg's). Why run a powerful engine if the full power is there when you ask for it? If the manufacture calls for premium, you're not getting the performance you paid for if you use regular. So even though I can use regular I always use premium so the power to be there when I need it, even if not every day.

[Bjkearns]

Re: Which Grade of Fuel Do You Use?

91 octane Chevron