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Owners manual says to use at least 91 octane fuel

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Psylence

Banned
I've got a '90 Cadillac Deville with just over 100K miles. The owners manual says not to use any fuel that has less than 91 octane, not sure why...

Here in Texas my choices are 87, 89, or 93, so I'm stuck having to pay for 93. Think it would harm anything if I used 87 or 89?
 
SHould be ok to use 89.. if your car makes pinging noises when you drive, go back to the high octane.

It's kind of sad how much I drive. My 2000 Toyota already has 50,000 miles on it. ::Q
 
Thanks amnesiac! Just gave you a 10! 🙂 Do pinging noises actually harm a vehicle, or is it just a matter of hearing an irritating noise?
 


<< Thanks amnesiac! Just gave you a 10! 🙂 Do pinging noises actually harm a vehicle, or is it just a matter of hearing an irritating noise? >>


No...

It's just engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders

from here
 


<< half a tank of 89 + half a tank of 93 = 91! >>



This is not true. I don't have a link to the website anymore, but some people who work with octane ratings said this would not work.
 
Pinging will cause the engine to run lean, which results in a loss of gas mileage and power. Also pinging can eventually be detonation which destroys your engine. Be safe and use 93.
 


<<

<< half a tank of 89 + half a tank of 93 = 91! >>


This is not true. I don't have a link to the website anymore, but some people who work with octane ratings said this would not work. >>



Dang...okay, I waded through the article on Encyclopedia.com and here's what I could gather from it:

Mixing 89 + 93 doesn't work because octane isn't a percentage of anything or an amount of anything. Rather, they burn a sample of the gas under controlled conditions until it starts knocking.

Then, under the same conditions, they experiment with different blends of an isooctane that is very resistant to knocking and a form of heptane that knocks very easily.

When they find the one that matches, the octane number of the fuel sampled from is the percentage of the isooctane in the blend...

Could have interpreted wrong though, here's the link to the article
 


<< You realize you are whining about $1-$2 difference per tank, right??

amish >>




1.50/tank x 3 tanks/2 weeks x 26= $117/yearly. 🙂
 
Older cars would make that noise if you would drive to a place at different altitude, so cars from Denver, for example, would make that noise when driving in LA. Better gas would help.
 
If your car has a knock sensor and you use cheaper fuel a couple things will happen.
If the ecu detects knock it will retard the timing, and dump more fuel to get rid of knock. This equates to loss of power and worse fuel economy.
You might as well fork over the 2 bucks per fill up and get better gas.
 
Of course you can blend gas from the same manufacturer, I used to do it all the time.
I finally stopped 'cuz it was just a hassle.
It's not a good idea to always use a lessor than required octane gas. You can get away with it once in awhile if you
are very gentle on the gas pedel.

BTW, some people use a higher than requred octane rated gas b/c they want to "treat their car right". It does NOTHING extra for your car.
 


<< << Thanks amnesiac! Just gave you a 10! Do pinging noises actually harm a vehicle, or is it just a matter of hearing an irritating noise? >>


No...

It's just engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders >>



Knocking and pinging can certainly damage your engine! It canl blow electrodes off of sparkplugs, and can put holes in pistons. It's definately less than desirable..


<< Pinging will cause the engine to run lean, which results in a loss of gas mileage and power. Also pinging can eventually be detonation which destroys your engine. Be safe and use 93. >>



How does pinging cause the engine to run lean? Pinging can be caused from the engine running lean, but not as a result of it..

pre-ignition, or detonation, is more severe than pinging, yes. However, running lean isn't going to lead to the buildup of deposits that would cause this. Running rich will, though.

You will probably find that 89 will be okay most of the time. Going up a stready grade, or doing any towing/hauling is where you might run into problems.
 


<< Of course you can blend gas from the same manufacturer, I used to do it all the time. >>


I wasn't saying you couldn't mix them...just that mixing equal parts 87 and 93 doesn't necessarily get you 91 🙂
 
another reason is that at places that don't move much fuel, the octane rating can degrade with time. If its been sitting there a while and you get 93, you will still have 93. Also, it costs a lot more to rebuild an engine with a detonated cylinder than it does to put a few extra bucks of feul in.
 
Believe it or not, an engine makes the most pwer with a light ping. ( ping and detonation are the same thing ) it is caused when the fuel lights witout the spark plug setting it off. The "ping" is 2 flame fronts coliding in the cyl. If the ping gets bad enough it can knock holes in pistons, and blow off electrodes. Every "ping" is roughly equivalent to smashing the piston with a hammer ( instant pressure on the piston, all released at once ) and smoothing that pressure over the downward motion of the piston.

If your car does not ping, you are fine. Ping will be most noticable at 2 points. WOT and light thottle. ( WOT = Wide open )
 
Most cars today are engineered to run on the cheap fuel, and can even cause check engine light to come on if you run Premium. So you can spend say 15-20 grand on a new car and save 100 dollars a year on fuel.... well maybe thats not such a great deal. 🙂
 


<<

<< Of course you can blend gas from the same manufacturer, I used to do it all the time. >>


I wasn't saying you couldn't mix them...just that mixing equal parts 87 and 93 doesn't necessarily get you 91 🙂 >>



You're right, because the average of 87 and 93 is 90, not 91.
 
If you're going to run with lower octane, make sure your car has a knock sensor for the engine. Don't assume that it does. Also, older cars are a lot more sensitive to lower-octane gas than newer ones. If you hear pinging, don't take any chances (unless you don't mind junking the car) - use the 93 octane. If you want to know if your car is pinging, try going up a steep hill with your a/c on.
 
I'm not sure your car, but with mine (Max) the recommended fuel is 91+ and like you i'm in Texas so i use 93. It can run on 89 as well, the ECU will just adjust the timing accordingly. Of course a loss in power is expected but at least it doesn't ping and you can reliably run with the lower octane for a certain amount of time. (e.g. when you absolutely, positively have to use the lower octane gas)

 
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