SpyderJeep

So I see we have a bunch of different views on Octane and it's value.

I want to do a large scale study with everyone who can figure MPG and log all results.

I think 3 tank fulls of each would be a fair average.

First run your currant octane fuel for 3 full tanks then switch to the other end and run the other octane fuel for 3 tanks full to full.

Record the miles driven, gallons used, price per gallon and the octane number.

I have a Excel spreadsheet I can share if anyone wants to use to make it a little easier to enter data for yourself, I will be using it to tally all of our data.

I have 2 XJ's that I will be using to test on.

I did this some years ago with my 240 Volvo and found out it was cheaper to run the 91 octane over the 85. Price Per Mile or PPM we'll call it.

Thanks and I hope we all can learn more about this touchy subject.

White92

Engines are designed to run on 1 specific octane. Some regular, and some premium. By running an engine designed for 87 octane (4.0L and 99% of all engines ever made) on 93 octane your vehicle will retard the ignition timing to adjust for the new gas to prevent spark knock. Therefore you aren't gaining much from running premium in a jeep.

SpyderJeep

Thanks for the info... I'm trying to do a study to SEE the results of a wide range of drivers.

ikenchute

you're 1/2 right but backwards.
running a higher octane will not cause your pcm to retard timing to stop a knock that isn't there.
running a higher octane will not cause spark knock in an engine built to run on a lower octane, but running a lower octane in an engine built for a higher octane will do just what you said.

1996XJSport

I'm getting 13-15 mpg in my XJ as of right now.

ToasterOnWheels

Im getting 20mpg average in a 99 5 speed xj and 17mpg in a 97 xj country aw4.

prerunner1982

Spyder... something else you will need to account for is the use of E10 vs Non Ethanol. To get the best results it would be best for everyone to run the E10 since it should be available almost everywhere, while non ethanol may not be available to everyone. If one person used non ethanol and others used E10 the results would be skewed.

Using the same octane, non ethanol will give an increase in MPG vs E10.

Using E10 in my 93 4x4 4.0 5 speed XJ I was getting consistently 20mpg. Going to Non Ethanol increased my MPG to 23mpg.

letinsh

Dude, I'm in. Another thing to consider is that no other repairs or upgrades should be done during the test, to get consistant test conditions. Also, note what type of driving you're doing (city v. hwy).

Ender

I drive a Jeep, I don't care about MPG... haha

LegalizeFreedom

That makes no sense. I drive a jeep, that uses to much gas. This whole thread makes no sense. Regular octane, now on to other ways to increase mpg's...

Ender

SpyderJeep

I see a few have missed the point.
I just want as many drivers to record data using both octanes.
Even if the data comes from a daily driver that is not a XJ or a Jeep.

White92

oops. ya higher octane in an engine designed for lower octane wont cause a knock

You caught me slipping.

DocOrng XJ

i already tried this in my 87 already - about 9 months ago-ish..
i keep close eye on my gas and write down every fill-up, car wash, and part/fix with dates, prices, times & mileage
then input them in a excel spreadsheet on my computer daily

to do this right you will also need to note ethanol gas vs non-ethanol gas
and need to know approx how much weight the vehicle carries / weighs
and city vs hwy miles
and gear ratio
and tire size
and actual mileage

My results as follows:
i actually gained mileage by using the "crappiest stuff" i could find


first thing i did a complete tune up - all new parts where applicable - nothing re-used

a) fuel tank additive / cleaner
drove for about a week then after giving it a fill up on regular 87 from E to F:

day 1)
1. 4 new Tires - 205 70 R15

2. Radiator Flush / Re-Fill 3. Thermostat & Gasket

4. Air Filter 5. O2 sensor, Spark Plugs, Wires and Cap & Rotor

day 2)
6. Oil Change #1 5qt 10w-30 + 1qt ATF & Oil Filter

week 5
16. Oil change #2 after driving 750 miles
6qt 10w-30 & Oil fiter

17. Stator & Ignition control module


I started my research with 97 - used the same station every time and pretty sure all the fill ups were in the evening (cause I was coming home from work) and they were all "on the same pump"

(at the time of research)
1987 4 door with 77xxx miles on it
2" lift stock tires, stock gears, no extra weight, mostly city driving

3 tanks of 97 - 16.3
2 tanks with 93 - 17.2
and then 2 tanks with 87 - 18.5+

and that was the best results i got, period

i did find a station that was doing no ethanol a few weeks later
3 or 4 tanks with 87 no corn crap 19.5+

then they switched on me and i noticed cause my mpg went down and i thought something was wrong with my baby, when i went to the pump my g/f noticed brand new stickers saying 10% ethanol on the pumps

Currently:
I have a 1987 4 door with (currently) 88xxx miles
18+ mpg
HWY(70%) / City (20%) / Rescue (10%) Mix
Rescue includes speeding on hwy/city to get to fire/fire house or on the trails looking for lost hikers
I use my vehicle on a farm & as a emergency search & rescue pov
I probably have an extra 500lbs+ in the rear; i keep it loaded down with extras like rescue / fire gear, fire extinguishers, food & tools
i have skid plates and a class V trailer hitch.
I am running on stock 3.07 gears with 31x10.5 tires and 3" lift.


and yes all these numbers are with an exhaust leak (still) in the #6 pipe and stock injectors

hope this helps

SpyderJeep

Wow!
Thanks DocOrngXJ
That is a lot of info.
That is the kind of data I'm looking to collect. Maybe more them I was thinking of.
Great info.