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Unread 07-03-2010, 10:11 PM   #1
pt2005
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2014 WK 
 
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Can I sometimes (or full time) use 91 gasoline?

Hi,

I've been using 87 on my KJ since day one. Heard from some friends (I am not mechanically inclined as you may tell ) that sometimes switching to a full tank of 91 will help clean the fuel system and give it a boost. Thought it a good advice; however, I remember vaguely the KJ manual says something like the car is designed for 87 and using high octane gas may harm the engine. Thats why I never used 91.

Another question I have is: I've been swinging between Chrevon, Shell, Mobil, 76 (and sometimes Arco). I noticed 76 seems to give me the highest mpg. But I am not sure if I am right because I don't have any data to back up. Any advice on the best gasoline name to use?

Thanks a bunch

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Unread 07-03-2010, 10:40 PM   #2
TheTJCometh
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A Jeep is like a Glock... It likes to be dirty. Seriously, I use 87 with no problems. I also go ethanol free. That would concern me the most.
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Unread 07-03-2010, 11:02 PM   #3
tjkj2002
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If your not chipped or towing 87 will just fine.
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Unread 07-04-2010, 03:21 PM   #4
CATCRD
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Higher octane gas is only to prevent pinging in engines with high compression or advanced timing, which a stock 3.7 doesn't have.
It doesn't clean out anything or give you a boost, so you don't need to run it. Your friends are misinformed. It won't harm your engine though.
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Unread 07-05-2010, 03:34 PM   #5
davegt
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I tried switching a few time to 91 and it seemed to me like i got better gas milage....not sure if i did or if i was just driving better (slower).
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Unread 07-06-2010, 08:46 AM   #6
rdc363
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I was told by a mechanic that higher-grades burn hotter and it may not be good for my Liberty.. Someone please correct him, if this is untrue.
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Unread 07-06-2010, 12:31 PM   #7
Turbobearcat
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Once in a while it's fine, I seen little difference between the two grades outside of cost!
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Unread 07-06-2010, 07:01 PM   #8
tjkj2002
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Quote:
Originally Posted by rdc363 View Post
I was told by a mechanic that higher-grades burn hotter and it may not be good for my Liberty.. Someone please correct him, if this is untrue.
Not true.
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Unread 07-08-2010, 12:29 AM   #9
LibertyTC
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Running higher octane, many will say is a waste of money.
If you are trying to clean your motor out of the carbon caused by constant city traffic..here is what is good to do...
Go to Chevron.with a half a tank of premium fuel, get a bottle of Chevron Techron, add that to your half tank, and take the jeep for a good highway run. That will help to clean out injectors and carbon off valves etc. I do this twice a year and my motor purrs like a kitten.
Running with synthetic oil and quality filter, will give you good fuel mileage as well.
I often run mid grade fuel. It seems to start easier, but dont let you jeep run all the time in the city.
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Unread 07-09-2010, 11:09 PM   #10
1badxj
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One instance where it can really make a difference, especially in naturally aspirated gas engines, is if you're at high altitudes for an extended period (above 7,000ft) the higher up you go, the more noticeable it is. That is the only time where I have ever noticed an increase of power/performance/and economy when using high octane.
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Unread 07-10-2010, 07:19 PM   #11
T-birdJunkie
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This is ThunderbirdJunkie's take.

Engine has a knock sensor. The engine's management software is programmed to advance timing until the engine starts pinging.
It will ping sooner with 87 than it will with 89 or 91.

ThunderbirdJunkie has documented in his logbooks that he saw about a 10% jump in fuel economy when going from 87 octane "wherever sells gas" to 89 octane Shell.

Advancing timing increases horsepower and efficiency (to a point).

BUT;
Premium will NOT "clean out" your fuel system or anything like that.
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Unread 07-11-2010, 05:10 PM   #12
tommy2399
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Well one thing to remember is that the higher octane burns slower. The wierd thing is that performance cars and some turbos cars like the slow burn.



The higher the octane the longer it will burn as it's pushes the piston down. Where as 87 octane will burn faster. Clear as mud
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Unread 07-11-2010, 08:13 PM   #13
T-birdJunkie
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It doesn't burn SLOWER, it has a higher flash point.

The higher cylinder pressures of a turbocharged/other high performance engine requires a higher flash point of the fuel to prevent detonation.
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Unread 07-11-2010, 10:48 PM   #14
tommy2399
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In most of the U.S., regular gas has an octane rating of 87, midgrade gas is 89, and premium is 91 or 92. (Octane ratings are lower in the mountain west due to the effects of thin air on internal combustion.) Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.

The majority of cars are designed to run on regular gas, and that's what the manuals tell the owners to use. Higher-performance cars often require midgrade or premium gas because their engines are designed for higher compression (higher compression = more power), and regular gas may cause knock. If your car needs high-octane gas, the manual will say so.
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Unread 07-12-2010, 03:56 AM   #15
scottunangst
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i think some of you are mistaking the properties of octane. the higher the octane the more resistance to burn, not the speed of the burn. the higher the octane the less likely to ignite from compression or a hot valve or carbon deposit in the combustion camber thus letting the timed spark control ignition. also some hi grades of gasoline do contain a small amount of detergent.
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