87 89 91 or 93 Octane?

06LibertySSE · **Posted:** Fri May 04, 2007 12:15 pm

Has anyone noticed if Higher Octane fuels will either INCREASE fuel economy or LESSEN fuel economy? What is everyone using in their Libertys??? On the highway my EVIC says Im getting 18.4 MPG on 87 and about 15.1 in the city... It seems like it should be more than that... Not heavy on the gas either... Thanks!

hyedipin · **Joined:** Thu May 11, 2006 10:20 am **Posts:** 1667

I have been getting 14.8 just increased to 15.2 after long drives.
Octane will have nothing to do with your mpg. Matter of fact, faster igniting "cleaner!?!" higher octane gas is actually bad for your jeep. There have been urban legends that the high octane usage caused on board computer to act up, ding for no reason, etc.

After all your jeep is designed to use cheapest gas there is. Check your manual.

06LibertySSE · **Posted:** Fri May 04, 2007 12:30 pm

I did check the manual, it stated 87, but I didnt know if anyone was having better results or performance with higher grade gasoline. Thanks for the response!

hyedipin · **Joined:** Thu May 11, 2006 10:20 am **Posts:** 1667

Even if it was giving you better mpg, believe me, it would even itself out or even cost more to buy higher octane gas... talkin about 40 cents here..
Forget about mpg (if you can afford it) and enjoy the jeep.

carroll952 · **Posted:** Fri May 04, 2007 12:33 pm

Yup, I use 87 here in Cali or 86 when I visit my folks in Albuquerque. The manual also reccomends using 89 octane for towing. As for MPG, I don't have an EVIC so I calculate it when I fill up. I usually average 16 or so in the city, sometimes as bad as 14 if I hit alot of bad LA traffic. On the highway I usually drive to Fresno (about 270miles) and get around 19-20. The best I've had was from Monterey to Santa Barbara at 21.9mpg. This is in a bone stock KJ with my original SRAs. However I'm getting a lift and bigger tires on the 20th so I only see this going down.

Justin

06LibertySSE · **Posted:** Fri May 04, 2007 12:38 pm

Dont get me wrong... I LOVE MY JEEP! It costs me about $60 bucks to fill up cuz I have the larger fuel tank (20.5 vs 18.5 on the older Libertys) Its definetly not a fuel efficent car to say the LEAST! Still the best vehicle I have ever owned!!!!

jcphoto20 · **Joined:** Sun Nov 19, 2006 1:36 am **Posts:** 507

loaded limited here, 87, i wont stay in a city long enough to figure fuel mileage there, upper 19s in the mountains, 25 hwy. i still have a few things to do, but i get tons better than most people.

hyedipin · **Joined:** Thu May 11, 2006 10:20 am **Posts:** 1667

06LibertySSE wrote:

Dont get me wrong... I LOVE MY JEEP! It costs me about $60 bucks to fill up cuz I have the larger fuel tank (20.5 vs 18.5 on the older Libertys) Its definetly not a fuel efficent car to say the LEAST! Still the best vehicle I have ever owned!!!!

You are lucky, so you can fill up when it's cheaper

My tank is supposed to be 19.5 as per my build sheet, but I can never get any more than 16 at "0 miles to Empty" on evic.....

scoobysnax · **Posted:** Tue Aug 14, 2007 5:50 pm

I use 87.

B/c this thing is 4,000lbs (!!!!!) I'm very slow on the gas knowing that during acceleration is when you're getting the worse gas mileage. With that said I live in NYC and my driving is 50/50 city/hwy. I've been avg about 17.8 - 18.7 a tank (only about 10 tanks since I've owned her) which I think for a liberty is pretty good. Best tank I have gotten so far is 19.5 on mostly highway. (Although when I did the miles driven/gas added formula it was closer to 19.1.)

For giggles reset the MPG computer when I'm in bumper to bumper stop and go traffic and I was shocked to get about 8 or 9 MPG and even worse if I have the AC going. I'll never do that for giggles again.

The best I've gotten was 25.4 mpg for a total of about 50 miles on a trip out to Long Island. Cruise Control was set at 60 (I wasn't in a rush and there were lots of cops out) and it's pretty much flat on the LIE (495.) I have roof rails but not a rack and everything else is stock '04 Limited with about 30,000 miles.

ATXKJ · **Posted:** Tue Aug 14, 2007 9:03 pm

50 Cetane if you can find it - or a good 5% biodiesel... oh you guys are talking about gasoline - - skip the bio - doesn't work well.

Actually - for a gas engine - the lowest Octane you can run without knocking is the best - although from a practical matter - you'll only hear knocking if your antiknock sensor is dead.

Octane's resistance to knocking is also resistance to burning - it's a value when it allows you to run a higher compression ratio - or more ignition advance - however once you get to the point of no knocking, then increasing the Octane will slow fuel air burning therefore making lower cylinder pressure and less power.

So unless the engine has a problem such as dirty injectors, carbon buildup or bad sensors you'll get more power and mileage from a lower Octane.

(However for towing you need a higher Octane the engine is trying to increase the ignition advance to make more power at a slower engine speed - and it's hotter) - what the manual says

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

I actually get the best milage out of 93, but my timing is very aggressive.

ATXKJ · **Posted:** Fri Aug 17, 2007 4:27 pm

KY -
I haven't followed all of your mods - but I was under the impression that you weren't anywhere close to stock.

yes - if you tweak it - compression or timing - higher octane will run better and keep you safer - knocking can punch holes in pistons - my brother used to keep a couple of spares with holes in them - but they were Chevy 11:1's and the timing advanced too far...

from an engine dynamics standpoint if the lower octanes give worse mileage - then the pressure from combustion is arriving at the piston before top-dead-center - maybe not enough to trigger a knock sensor - but enough to reduce overall power - the higher octane slows the ignition so that it builds pressure for the downstroke - not on the upstroke.

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

ATXKJ wrote:

KY -
I haven't followed all of your mods - but I was under the impression that you weren't anywhere close to stock.

yes - if you tweak it - compression or timing - higher octane will run better and keep you safer - knocking can punch holes in pistons - my brother used to keep a couple of spares with holes in them - but they were Chevy 11:1's and the timing advanced too far...

from an engine dynamics standpoint if the lower octanes give worse mileage - then the pressure from combustion is arriving at the piston before top-dead-center - maybe not enough to trigger a knock sensor - but enough to reduce overall power - the higher octane slows the ignition so that it builds pressure for the downstroke - not on the upstroke.

Yeah, I'm no where near stock. About $10k in performance and handling mods as long as you don't count the motor sitting in the garage. Mine will run on 89, but it runs much better on 93. It really doesn't like the taste of 87.

onejohny · **Posted:** Sat Aug 18, 2007 1:50 pm

06LibertySSE wrote:

Has anyone noticed if Higher Octane fuels will either INCREASE fuel economy or LESSEN fuel economy? What is everyone using in their Libertys??? On the highway my EVIC says Im getting 18.4 MPG on 87 and about 15.1 in the city... It seems like it should be more than that... Not heavy on the gas either... Thanks!

I get about 10% higher mileage with 87 as compared to 93. I've done this on several tanks of gas and I get 21-22 on 87. When I go to 93 I get less than 20 consistently.

It has more power with 93. I'm going to try 89 one of these tanks and see if it's a reasonable compromise.

Joe Romas · **Posted:** Thu Sep 20, 2007 10:47 am

hyedipin wrote:

Even if it was giving you better mpg, believe me, it would even itself out or even cost more to buy higher octane gas... talkin about 40 cents here..

Depends. I also own a VW Eurovan and the later engines, not my 93, call for premium fuel. Several people have done long term caculations and for these cars any how it's actually cheaper to use premium fuel :shock:

I think it works out to $150 savings per 100k miles. Not a lot but still cheaper :lol:

87 89 91 or 93 Octane?

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