What Octane do you use?

[powerslave1966]

I was wondering if you all have noticed a difference in gas consumption between Regular (87) Mid-grade (89) and Premium (92) fuels.... this is a purely "eyeball/guesstimate" reading, but the XK is currently being used as my primary work vehicle, no other trips or errands, and if I use regular, a full tank will last exactly one week. However, if I fill up with premium, I am able to get almost exactly two weeks use! Yeah I'm paying more for premium, but I feel that I'm getting alot more benefit from it vs. regular... What's you guy's opinion?????

BTW, I'm running the 3.7L (4X4) with K&N drop-in air filter, RC 2.5" lift and Mickey Thompson 265/70/17 Baja MTZ.....

[Sal-XK]

I've done tests on my wifes car before and did get slightly better mileage on the premium just enough to cover the extra cost but double the distance makes no sense to me.

[powerslave1966]

I've done tests on my wifes car before and did get slightly better mileage on the premium just enough to cover the extra cost but double the distance makes no sense to me.

Like I said, its not an "exact measurement", I have not yet done mpg statistics or written down every single red light that I encounter; but the wife can easily back me up and say the same... I will be doing a test soon though, when I have to fill'er up again, i'll use regular, and then premium the next time...

[Sal-XK]

I know its hard to an accurate read on the results with so many variables and stuff. I did my wife's car while on a road trip so it was a little easier and more straight forward test all highway miles. But if you can at least take the same route to and from work on two separate tanks gas you can at least get an average. Like I said I did experience a gain in mileage which meant I had to stop less for fill ups and I did get more then enough mileage to pay for the extra cost. Also I think the XK is meant to run on 89 octane so I'm curious to see what you get out of it. Looking forward to your results.

[LWM]

I used to use premium exclusively and when I purchased the Superchips I changed the settings and now run 87. If you use a program like fuelly in my signature it will help monitor your mileage.

[06blkhemi]

I run the mid grade,it's only like .10cents more then regular.. I'm getting 240miles to a tank with about 3 gal.left in the tank.. I noticed with the midgrade it seems to run smoother too ..Regular made it feel more "draggy"..

[powerslave1966]

I run the mid grade,it's only like .10cents more then regular.. I'm getting 240miles to a tank with about 3 gal.left in the tank.. I noticed with the midgrade it seems to run smoother too ..Regular made it feel more "draggy"..

Not bad for a hemi... I like to fuel up with premium and dump a bottle of seafoam when we go on trips.....for some reason I was under the impression that the XK's had a 5 gallon "Reserve" ....

[WanderingTs]

I have a 4.7L flex fuel. I conducted an extremely unscientific couple of tank average using E85 (85 octane ethanol). I know it is not a direct comparison to fossil fuels, but here's what my averaged numbers at the time told me -

A tank of E85 did not give me as many miles per tank, but was about 30 cents a gallon cheaper.

A tank of 87 octane gas got me more miles per tank, but cost about 30 cents a gallon more.

I don't have my numbers anymore, but after the math, my price per mile for fuel turned out to be statistically the same, within the margin of error for my methods. Since I don't like to stop at filling stations, and the E85 station is not easy for me to get, I almost exclusiely burn 87.

While towing, I have noticed that I don't seem to have to bury my foot in the accelerator as much climbing hills with 89, so occasionaly I splurge there. I have never run real numbers on MPG doing that, it is just an opinion based on the subjective feel of the gas pedal.

[powerslave1966]

Ok, so I filled up at Sam's Club after returning from work with 93 octane today, got 44950 miles on the mileanometer, let's see how this goes....

[strokeZ]

I run only 89 or better. WanderingT's - 30 cents is not nearly enough of an offset to justify E85. I experienced an average 2mpg decrease with E85 when I decided to test it out. So back when 89 octane was running $3.00, I calcuated that E85 had to be no more than $2.40 to justify. Now I did feel a lot better throttle response with E85, but I am sure that was becuase it has a 105 octane rating. E85 is great for cars specifically designed for it bc the exhaust temps are cooler so you can theoretically crank up the compression and actually get more HP, but Flex fuel cars don't do that, they just change the firing, etc. Make sure that if you DO test you go through at least 2 to 4 tanks for the electronics to fully kick in.