First off I wanna say I love this site and everybody that has helped me. Here is my next question. What grade of fuel should I run 89 or 91 octane? The beast has 130000 mi on it.

Jay

 

I guess what ever your wallet will allow.....

 

Not sure about California, but around here the higher octane stuff is usually the less expensive since it's ethanol blend.

Both run fine in my Durango, but obviously ethanol blend gives you slightly lower gas mileage. I did the calculations a couple years back and I think the number I came up with was that ethanol blend had to be 8 cents a gallon cheaper before it actually started saving me any money. (EDIT: Now that I think about it, the 8 cents might be the number I came up with for when it started making sense for a buddy of mine to put E-85 in his flex-fuel tahoe. I'll have to run the numbers again on E-10 in regular engines.)

If we're not talking about blends, just straight gasoline with different octane ratings, just take a peek at your owner's manual and see what it says.

Some performance cars have higher compression engines and actually require the higher octane fuel to avoid engine knock. In general, if you don't have one of the engines that requires it, there's no advantage to paying extra for it.

 

All engines other than a few 2000 5.9L R/T Durango’s use 87 octane fuel. This is normal low grade fuel at lower altitude. There were a few 2000 R/T Durango’s that when the R/T first came out the PCM had a more aggressive tune. This specific tune required the use of 91 octane. On these few numbers of 2000 R/T Durango’s the 91 octane requirement, the 91 octane must be labeled on the inside of the fuel door as well as labeled in the instrument cluster thus not to hide this special requirement to the end comsumer. All engines, unless identified as other, are built to the regular fuel 87 octane requirement at sea level. That is Federal Comsumer Protection Law.

As you increase in elevation the octane levels lower by 2 points, however the fuel is still the same. So at low elevation regular fuel is 87 octane, the same fuel at 4500 feet in elevation is only 85 octane. The Durango will run on the regular 85 octane in high elevations. Now if the motor starts pinging, then just fuel up the next octane level (87) and see if that eliminates the issue.

In retrospect, premium fuel at low elevations is 93 octane, the same fuel at 8000 feet is again <-2 to become 91 octane, even though it's the same fuel.


There is a reason to use higher octane fuel however; with higher octane you get a cleaner burn. The higher the octane the slower more concise burn the fuel will burn. Most PCM's will see this and make changes to the fuel/air mixture so in reality you will get little improvements, however there will be some improvements. Most likely not enough to save you any money over the fuel costs.

Due to the slower burn, engine ping (or pre-ignition) will stop because the actual detonation of fuel/air will be slightly later (retarded timing) thus bringing the advanced TDC closer to the top of the cylinder.

Simply by getting more concise burn comes a cleaner more powerful burn thus increasing some slight power. This means that while going down the road you might see an improvement of a slight fuel mileage increase, and I mean slight. However when towing you use more fuel. SO while towing I used to always use the higher octane (Premium Fuel) as I could. This made the trucks motor burn more efficient thus creating more torque with less fuel. I did notice an improvement.

During towing I always try to use Chevron 91 octane or better, just seems to run better and more power. However I don't worry about it now with my V-10 because it's a fuel hog and it makes enough power on its own.

 

hydrashocker is right, but I also stand by what I said.

In hindsight, instead of "no advantage" I should have said "very little advantage" to running high octane when it's not required. Probably not enough advantage to justify the extra cost except in special situations like towing (as hydra mentioned).

 

Running a couple of tanks of premium now and again also helps clean the fuel system as the additive used to raise the octane also have a detergent quality and are not as hard on some fuel system components as some of the fuel cleaners you pour in your tank.

 

unless you have an R/T regular grade gas should be just fine in the engine, if you ahve a pinging/knocking problem then try the higher octane

 

I think that is incorrect for the most part. I don't know of anyone that puts in more detergents then is necessary. Just Google it.

The reason it burns slower.

http://auto.howstuffworks.com/premiu....htm/printable
http://www.straightdope.com/columns/...nd-regular-gas
http://en.wikipedia.org/wiki/Octane_rating
http://www.edmunds.com/fuel-economy/...icleid=106293&
http://autos.aol.com/article/87-octane-gas/
http://www.fraudguides.com/tips/june2.asp
http://www.cartalk.com/content/featu...ium/myths.html

 

Learn something everyday. I was just passing on what my instructors told me in my college classes fifteen years ago.

 

Well some companies might put a little more detergents in, but I don't know which ones and how much they might add?